WO2011142291A1 - 動画像符号化制御方法,動画像符号化装置および動画像符号化プログラム - Google Patents
動画像符号化制御方法,動画像符号化装置および動画像符号化プログラム Download PDFInfo
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- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
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- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
- H04N19/124—Quantisation
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- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/146—Data rate or code amount at the encoder output
- H04N19/15—Data rate or code amount at the encoder output by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
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- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
- H04N19/172—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a picture, frame or field
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- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/177—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a group of pictures [GOP]
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- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/189—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
- H04N19/192—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding the adaptation method, adaptation tool or adaptation type being iterative or recursive
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- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/189—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
- H04N19/196—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters
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- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/189—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding
- H04N19/196—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters
- H04N19/198—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters including smoothing of a sequence of encoding parameters, e.g. by averaging, by choice of the maximum, minimum or median value
Definitions
- the present invention relates to a moving image code for encoding a video signal so as not to cause a failure of a virtual buffer such as a coded picture buffer (CPB) in a virtual decoder and to prevent deterioration of image quality.
- a virtual buffer such as a coded picture buffer (CPB) in a virtual decoder
- CPB coded picture buffer
- the present application is Japanese Patent Application No. 2010-109874, Japanese Patent Application No. 2010-109875, Japanese Patent Application No. 2010-109876, Japanese Patent Application No. 2010-109877, Japanese Patent Application filed in Japan on May 12, 2010 Claims priority to 2010-109878, the contents of which are incorporated herein.
- a virtual decoder HRD Hypothetical Reference Decoder
- the H.264 encoder needs to perform encoding so that the virtual decoder does not fail.
- the present invention is a technique for reducing image quality deterioration while suppressing CPB failure of a virtual decoder, specifically, CPB underflow.
- Figure 1 shows a conceptual diagram of CPB underflow.
- an encoded stream is input to the CPB at that bit rate (reference code RS1 in FIG. 1).
- the data amount of the encoded stream in the CPB at each time is referred to as “remaining code amount”.
- the virtual decoder extracts the encoded stream corresponding to each picture from the CPB. In that case, the CPB remaining code amount is instantaneously reduced by the code amount corresponding to the picture.
- FIG. 1 shows an example of a fixed bit rate, the same applies to a variable bit rate.
- CPB underflow refers to a situation where the coded stream of the picture is insufficient in the CPB when the virtual decoder tries to extract the coded stream of the picture from the CPB.
- H. In encoding based on H.264, it is necessary to verify the CPB state while performing encoding, and to create a stream that does not cause CPB underflow.
- the CPB of the virtual decoder is H.264.
- the following non-patent document 1 describes further details.
- CPB Conceptual buffer
- MPEG Motion Picture Experts Group
- VBV Video Buffering Verifier
- Video signal encoding methods include techniques of 1-pass encoding and multi-pass encoding.
- the 1-pass encoding generally, pictures of an input video are sequentially encoded.
- multi-pass encoding an input video is encoded a plurality of times.
- the second encoding is performed using the result of the first encoding.
- the conventional technique of 1-pass coding will be described as “conventional technique a”
- the conventional technique of 2-pass coding will be described as “conventional technique b”.
- a quantization parameter that generates the maximum code amount that can be used for encoding the remaining video of the GOP is estimated from the remaining code amount of the CPB, and this is used to encode the encoding target picture.
- the present invention solves the above-mentioned problems, and reduces the CPB underflow with a smaller amount of computation than the conventional two-pass coding (conventional technology b), while the conventional one-pass coding (conventional technology a).
- the purpose is to reduce such a large image quality degradation.
- the encoding order picture group is a collection of pictures that are configured by a predetermined number of pictures and that are continuous in the encoding order.
- a typical coding order picture group is GOP (Group Of Pictures).
- FIGS. 2A to 2C Schematic diagrams of the coding order picture group are shown in FIGS. 2A to 2C.
- I is a picture to be subjected to intra prediction encoding (I picture)
- P is a picture to be forward predictive encoding (P picture)
- B is a target of bidirectional predictive encoding. Represents a picture (B picture).
- the display order of pictures is, for example, I ⁇ B ⁇ P ⁇ B ⁇ P ⁇ B... As shown in FIG. 2A.
- the coding order picture group referred to in the present invention is GOP
- the coding order picture group is a picture group of I ⁇ P ⁇ B ⁇ P ⁇ ... ⁇ B ⁇ P (immediately before I) as shown in FIG. It becomes.
- the coding order picture group has a 13 picture configuration
- 13 pictures consecutive in the coding order as shown in FIG. 2C are the coding order picture group referred to in the present invention.
- a group of pictures obtained by dividing a picture sequence of an input video into a picture group that is continuous in a coding order and is configured by a predetermined number is called a coding order picture group.
- the “picture” is a frame when the video is in the progressive format, and is a frame in which one field or a top field and a bottom field are combined in the case of the interlace format.
- the quantization statistic is a statistic obtained from the quantization parameter or quantization step used for encoding each macroblock of the picture. For example, the quantization parameter of the macroblock of the picture, the average of the quantization step, or the median.
- the encoding of the input video proceeds in units of encoding order pictures. However, each time an input picture is encoded, it is checked whether the quantization statistic of the picture exceeds a predetermined threshold, and if the quantization statistic exceeds a predetermined threshold, an encoding parameter is generated.
- the encoding order picture group being encoded is re-encoded by changing the code amount to be small.
- the trigger for outputting the encoding result from the output buffer is when the encoding of the encoding order picture group is completed.
- the coding parameters to be changed include, for example, quantization parameters and prefilter strength, and one or more of these are changed.
- quantization parameters and prefilter strength For example, in the case of a quantization parameter, the step size of the quantization parameter is increased so that the generated code amount of the encoding parameter is reduced.
- the filter strength of the pre-filter for the input video is changed, the generated code amount can be reduced by changing the blurring degree to a greater extent.
- the encoding parameter at the time of normal encoding means an encoding parameter determined when the state is not re-encoding.
- the encoding parameter is not necessarily returned to the value at the time of normal encoding, but the remaining code amount of the CPB is checked, and the remaining code amount is a predetermined threshold value. Only in the above case, the encoding parameter may be returned to the normal encoding value, and when the remaining code amount is small, the encoding parameter may not be returned to the normal encoding value. In this way, the possibility of continuous re-encoding can be reduced.
- the encoding parameter is basically returned to the encoding parameter value at the time of normal encoding.
- the encoding order picture group is re-encoded, Each time the quantization statistic of the picture exceeds a predetermined threshold, and if the quantization statistic exceeds the predetermined threshold, the head of the encoding order picture group currently being encoded is checked. It is also possible to re-encode by changing the encoding parameter from this picture. That is, as long as the re-encoding condition that the quantization statistic exceeds a predetermined threshold is satisfied, encoding is repeated a plurality of times for the same encoding order picture group.
- the value of the retry count is increased when re-encoding occurs, and encoding of the encoding order picture group is completed Decrease the retry count value.
- the value of the encoding parameter described above is set according to the size of the retry count, and a value that reduces the generated code amount as the retry count increases is used.
- the encoding parameter is a quantization parameter
- the step size is increased as the retry count is increased.
- the encoding parameter is the filter strength of the prefilter, the blurring degree is increased as the retry count is increased.
- the video to be encoded has a complex part and a simple part.
- the more complicated the video the greater the amount of change in the generated code amount due to the change of the encoding parameter.
- the amount of fluctuation in image quality is large. If re-encoding for one encoding order picture group is determined only once, when the re-encoding condition that the quantization statistic exceeds a predetermined threshold is satisfied and re-encoding is performed In order to prevent the re-encoding condition from being satisfied again, it is necessary to greatly change the encoding parameter at the time of re-encoding from the encoding parameter before the re-encoding. In this case, when a relatively complicated portion of the video is a target of re-encoding, there is a possibility that a large image quality deterioration occurs.
- the encoding order picture group is repeatedly encoded, the retry count is managed, and the encoding parameter is set according to the size of the retry count.
- the change amount of the encoding parameter is suppressed to be small, and encoding is performed with an appropriate encoding parameter.
- image quality degradation can be further reduced.
- the number of re-encoding operations for one encoding order picture group is managed by a parameter called retry count, and when re-encoding occurs, the retry count value is increased, and encoding of the encoding order picture group is completed. Reduce the retry count value.
- the CPB remaining code amount is set to a predetermined threshold value when encoding of the encoding order picture group is completed. Only in the above case, the retry count may be reduced.
- the retry count is decreased to the next encoding-order picture group. Reduce the impact of image quality degradation. However, if the CPB remaining code amount is less than the predetermined amount, the retry count is not reduced. This reduces the possibility that re-encoding will occur in the encoding of the next encoding order picture group.
- the coding order picture group is a collection of pictures that are composed of a predetermined number of pictures starting from an intra-screen predictive coding picture (I picture) and are consecutive in the coding order.
- the encoding order picture group does not necessarily have to be a GOP, but the leading picture of the encoding order picture group is an intra-picture prediction encoding picture (I picture).
- FIG. 2D shows an example in which the coding order picture group has a 20-picture configuration for 2 GOPs.
- the encoding of the input video proceeds in units of encoding order pictures. However, each time an input picture is encoded, it is checked whether the quantization statistic of the picture exceeds a predetermined threshold, and if the quantization statistic exceeds a predetermined threshold, an encoding parameter is generated. The code amount is changed so as to decrease, and re-encoding is performed from the position of the encoding order picture group set as a retry point (described later). The output result of the encoding result from the output buffer is when the encoding of the encoding-order picture group is completed and it is determined that re-encoding is not performed.
- the coding parameters to be changed include, for example, quantization parameters and prefilter strength, and one or more of these are changed.
- quantization parameters and prefilter strength For example, in the case of a quantization parameter, the step size of the quantization parameter is increased so that the generated code amount of the encoding parameter is reduced.
- the filter strength of the pre-filter for the input video is changed, the generated code amount can be reduced by changing the blurring degree to a greater extent.
- the encoding parameter at the time of normal encoding means an encoding parameter determined when the state is not re-encoding.
- the encoding parameter is not necessarily returned to the value at the time of normal encoding, but the remaining code amount of the CPB is checked, and the remaining code amount is a predetermined threshold value. Only in the above case, the encoding parameter may be returned to the normal encoding value, and when the remaining code amount is small, the encoding parameter may not be returned to the normal encoding value. In this way, the possibility of continuous re-encoding can be reduced.
- the above-mentioned retry point is position information indicating from which picture re-encoding is started when it becomes necessary to re-encode due to a quantization statistic exceeding a predetermined threshold in a certain picture.
- the retry point is basically the first picture of the encoding order picture group that is currently encoded, but may be the first picture of the encoding order picture group encoded one time before.
- the opportunity to update the retry point is as follows. (1) If the remaining CPB code amount is equal to or greater than a predetermined threshold when encoding of the encoding order picture group is completed, the retry point is set to the first picture (I picture) of the next encoding order picture group . (2) When the encoding order picture group has been encoded and the CPB residual code amount is smaller than a predetermined threshold, the retry point remains unchanged and the process proceeds to the encoding of the first picture in the next encoding order picture group. . If the quantization statistic does not exceed a predetermined threshold in the encoding of the leading picture of the encoding order picture group, the retry point is set to the leading picture of the encoding order picture group that is currently encoded.
- the processing configuration becomes simpler than the present invention.
- this technology is referred to as “related technology”.
- image quality degradation can be reduced by re-encoding only the coding order picture group including the picture in which the quantization occurs only when the quantization statistic exceeds a predetermined threshold. it can.
- the second aspect of the present invention makes it possible to reduce image quality degradation of a decoded image more effectively than this related technique.
- an I picture has a larger amount of generated code than other picture types. Therefore, when the amount of remaining CPB code is small at the time when encoding of a certain coding order picture group is completed, in the conventional rate control, in order to suppress the generated code amount, The quantization parameter value used for encoding is increased. In such a case, in the related technique, re-encoding occurs due to the increase in the quantization parameter of the I picture, but re-encoding starts from the first picture of the encoding-order picture group currently being encoded. Therefore, it is necessary to avoid the establishment of the re-encoding condition with only the I picture itself. In this case, there is a problem that the image quality of the I picture itself is greatly deteriorated. Furthermore, since the I picture is referred to in the subsequent encoding of the P picture and B picture, the encoding efficiency of these P picture and B picture also deteriorates.
- the second aspect of the present invention when the amount of remaining CPB code is small, when the re-encoding condition is satisfied in the first I picture of the next encoding order picture group, Return to the previous coding order picture group and re-encode from the beginning. Therefore, it is possible to avoid the occurrence of large image quality deterioration in the first picture of the coding order picture group, and to reduce the image quality deterioration.
- the frame of the input video is not always encoded twice as in the conventional two-pass encoding, but the principle is one-pass encoding.
- re-encoding is performed retroactively for a plurality of pictures.
- the quantization statistic exceeds a predetermined threshold in coding of the pictures in the coding order picture group
- re-encoding is performed retroactively to a certain picture in the coding order picture group.
- Do. Which picture is to be re-encoded is determined in advance according to the amount of available memory.
- the maximum number of pictures that can be traced during re-encoding is defined as “maximum inter-picture distance”.
- the outline of processing in the third aspect of the present invention is as follows. First, the maximum number of pictures that can be traced at the time of re-encoding is obtained based on information on the amount of available memory given from the outside, and this value is stored as the maximum inter-picture distance.
- re-encoding it is necessary to store the video signal of the picture to be encoded in the input buffer, and it is determined that the re-encoding is not performed in the output buffer. It is necessary to hold the encoded stream of the encoding result until the output of the result is completed. If there is a sufficient amount of memory that can be used, the re-encoding condition is satisfied by having the input buffer and the output buffer each have a memory capacity equivalent to the number of pictures in the encoding order picture group. The time re-encoding can be performed from the top of the encoding order picture group with the encoding order picture group as a unit.
- the maximum inter-picture distance which is the maximum number of pictures that can be traced back during re-encoding, is calculated from the amount of memory that can be used in advance.
- the encoding of the input video proceeds with the encoding order picture group as a unit. However, each time an input picture is encoded, it is checked whether the quantization statistic of the picture exceeds a predetermined threshold, and if the quantization statistic exceeds a predetermined threshold, an encoding parameter is generated.
- the encoding order picture group being encoded is re-encoded by changing the code amount to be small. However, as to which picture of the encoding order picture group being encoded, the picture is to be re-encoded to satisfy the following three conditions. Condition 1: The picture is included in the encoding order picture group being encoded.
- Condition 2 The picture is included in the maximum inter-picture distance on the basis of a picture whose quantization statistic exceeds a predetermined threshold.
- Condition 3 A picture farthest from a picture whose quantization statistics exceed a predetermined threshold among pictures satisfying conditions 1 and 2.
- the retry point is, for example, the first picture in the current coding order picture group if the first picture within the maximum inter-picture distance is in the previous coding order picture group, otherwise the maximum The first picture at the inter-picture distance, that is, the oldest coded picture separated by the maximum inter-picture distance.
- coding parameters to be changed at the time of re-encoding for example, there are quantization parameters and prefilter strength, and one or more of these are changed.
- quantization parameters and prefilter strength For example, in the case of a quantization parameter, the step size of the quantization parameter is increased so that the generated code amount of the encoding parameter is reduced.
- the filter strength of the pre-filter for the input video is changed, the generated code amount can be reduced by changing the blurring degree to a greater extent.
- the image quality degradation is reduced to the next encoding by returning the encoding parameter to the encoding parameter value at the time of normal encoding. Suppresses spreading to the forward picture group.
- the encoding parameter at the time of normal encoding means an encoding parameter determined when the state is not re-encoding.
- the encoding parameter is not necessarily returned to the value at the time of normal encoding, but the remaining code amount of the CPB is checked, and the remaining code amount is a predetermined threshold value. Only in the above case, the encoding parameter may be returned to the normal encoding value, and when the remaining code amount is small, the encoding parameter may not be returned to the normal encoding value. In this way, the possibility of continuous re-encoding can be reduced.
- the coding order picture group is returned to the beginning, and the CPB residual code Since re-encoding is performed so that the amount increases, image quality degradation in a complicated scene can be reduced as compared with the conventional technique a of 1-pass encoding.
- the present invention reduces image quality degradation by partially re-encoding only when necessary, the conventional technique b of 2-pass encoding in which all frames of an input video are encoded twice; The amount of calculation is small in comparison.
- the amount of change in the encoding parameter at the time of re-encoding can be suppressed to be small, and deterioration in image quality due to re-encoding can be reduced.
- the encoding parameter is kept the same as that at the time of re-encoding, so that the occurrence of re-encoding can be suppressed.
- the encoding order picture group set as a retry point Since the re-encoding is performed so that the CPB residual code amount further increases, image quality deterioration in a complicated scene can be reduced as compared with the conventional technique a of 1-pass encoding.
- the present invention reduces image quality degradation by partially re-encoding only when necessary, the conventional technique b of 2-pass encoding in which all frames of an input video are encoded twice; The amount of calculation is small in comparison.
- the present invention can prevent the image quality of the first I picture in the coding order picture group from greatly deteriorating even when coding of the coding order picture group is completed and the amount of remaining CPB code is small. it can.
- the present invention even if the encoding process shifts from a simple scene of a video to a complicated scene and the image quality deteriorates due to insufficient CPB remaining code amount, it is set as a retry point in the encoding order picture group.
- re-encoding is performed so that the CPB residual code amount further increases, so that it is possible to reduce image quality degradation in a complicated scene as compared with the conventional technique a of 1-pass encoding.
- the present invention reduces image quality degradation by partially re-encoding only when necessary, the conventional technique b of 2-pass encoding in which all frames of an input video are encoded twice; The amount of calculation is small in comparison.
- re-encoding is performed from a retry point determined according to the amount of memory required for re-encoding, the memory can be effectively used.
- FIG. 3 is a process flowchart showing the moving picture coding control method according to the first embodiment of the present invention.
- a picture next to a picture that has been encoded in the input video signal is set as an encoding target (step S1).
- the input picture set as the encoding target is defined as H.264. H.264 and other predetermined encoding methods (step S2). It is determined whether or not the quantization statistic of the picture when the input picture is encoded exceeds a predetermined threshold (step S3). If the quantization statistic exceeds the predetermined threshold, the processing is performed. Proceed to step S7.
- step S4 it is determined whether or not the final picture has been encoded. If the encoding is completed up to the final picture, the encoding process is terminated.
- step S5 it is determined whether or not the encoding order picture group has been encoded. If the encoding order picture group has not been encoded, the process returns to step S1, and the encoding process is continued in the same manner for the next picture.
- the encoding parameter is changed by re-encoding (retry) of the encoding order picture group, the encoding parameter is returned to the value at the time of normal encoding ( In step S6), the process returns to step S1, and the encoding process is performed from the first picture in the next encoding order picture group.
- step S7 it is determined whether or not the current coding-order picture group has been re-encoded (retry has been completed) (step S7). ). If the retry has been completed, no further re-encoding is performed, and the process proceeds to step S4 to continue the encoding process.
- the first picture of the current coding order picture group is set as a coding target in order to re-encode the current coding order picture group (step S8). Then, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (the quantization parameter changes the step size more greatly, and in the case of the filter strength, the blurring degree changes more greatly) ( In step S9), the process returns to step S2, and the encoding order picture group being encoded is re-encoded.
- the two encoding parameters quantization parameter, prefilter strength
- the encoding order picture group (for example, GOP) is encoded twice.
- the video can be changed from a simple scene to a complex scene.
- the amount of calculation can be reduced as compared with the conventional technique b in which all the pictures of the input video are encoded twice, while reducing the deterioration of the image quality when moving to.
- FIG. 4 is a process flowchart showing a video encoding control method according to a modification of the present embodiment.
- the process of step S6 shown in FIG. 3 can be replaced with the processes of steps S61 to S63 shown in FIG. Processes other than step S6 are the same as those in FIG.
- step S61 it is determined whether or not the encoding parameter has been changed by retry. If the encoding parameter has not been changed by retry, the process returns to step S1 in FIG. If the coding parameter has been changed by retrying, it is next determined whether or not the CPB remaining code amount is equal to or greater than a predetermined threshold (step S62). If the CPB residual code amount is less than the predetermined threshold value, the encoding parameter remains in the state used for re-encoding, and the encoding parameter is restored to the original default encoding only when the CPB residual code amount is equal to or larger than the predetermined threshold value Return to the parameter (step S63). Thereafter, the process returns to step S1 in FIG. 3 and proceeds to encoding of the next encoding order picture group.
- the encoding parameter is set to the value at the time of normal encoding only when the CPB remaining code amount exceeds a predetermined amount when the encoding of the encoding order picture group is completed as described above. Return to value. This is due to the following reason. Even if encoding of the encoding order picture group is completed, if the CPB residual code amount is small, the generated encoding amount increases when the encoding parameter is returned to the value at the time of normal encoding. When the picture group is encoded, the possibility that the quantization statistic of the encoded picture exceeds a predetermined threshold again increases. In the process of FIG. 4, when the CPB residual code amount is small, the encoding parameter is not changed. Therefore, compared with the process of FIG. As a result, the amount of calculation is further reduced.
- the encoding parameter is changed during re-encoding.
- a pre-filter is applied to the input video during encoding, and the encoding parameters to be changed are a quantization parameter and a pre-filter strength. Both of these two encoding parameters may be changed, or only one of them may be changed.
- Quantization parameters are re-encoded with a larger quantization parameter by adding a predetermined offset value to the quantization parameter value during normal encoding.
- a Gaussian filter is used in this embodiment.
- the Gaussian filter can be created by sampling a Gaussian distribution represented by the following equation with respect to x and y.
- the type of the low pass filter is not limited.
- how to increase the degree of blurring during re-encoding may be arbitrarily determined in advance.
- the default encoding parameter ⁇ 0 may be changed in accordance with the complexity of each picture, and ⁇ 1 may be a value obtained by adding a predetermined offset to ⁇ 0 .
- quantization statistics in this embodiment, an average value of quantization parameters of each macroblock of a picture is used.
- Encoding is H.264. It is assumed that encoding according to the H.264 standard is performed. Further, in this embodiment, the encoding order picture group is GOP, and a conceptual diagram of the GOP at the time of encoding is shown in FIG. One GOP is composed of 10 pictures, and B pictures and P pictures are alternately arranged with the I picture at the head in the display order.
- FIG. 6 shows an example of the apparatus configuration of this embodiment.
- the input buffer 10 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 20. Further, when the input buffer 10 receives information (retry information) indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 40 described later, The video signal is output again to the encoding unit 20 from the first picture of the GOP being encoded. When the GOP encoding is completed without receiving the retry information, the input buffer 10 discards the stored video signal of the GOP.
- retry information information indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 40 described later
- the encoding unit 20 encodes the video signal input from the input buffer 10 and outputs the encoded stream to the output buffer 30. Further, the encoding unit 20 outputs the quantization parameter (quantization parameter information) of each macroblock when the input video signal is encoded to the quantization statistic calculation unit 40. Furthermore, when receiving the retry information from the quantization statistic calculation unit 40, the encoding unit 20 receives the video signal from the first picture of the GOP being encoded again from the input buffer 10, and also sets the parameter adjustment unit 50. Since the encoding parameter for re-encoding is input from, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 30 outputs the encoded stream of the GOP when all the encoded streams of the GOP are accumulated. On the other hand, when receiving the retry information from the quantization statistic calculation unit 40, the output buffer 30 The encoded stream accumulated for the GOP is discarded.
- the quantization statistic calculation unit 40 uses the quantization parameter information input from the encoding unit 20 to obtain a quantization statistic that changes in units of pictures. When the quantization statistic exceeds a predetermined threshold value, the quantization statistic calculation unit 40 outputs the retry information to the input buffer 10, the encoding unit 20, the parameter adjustment unit 50, and the output buffer 30 for quantization. Notify that the statistic exceeds a predetermined threshold.
- the parameter adjustment unit 50 When the parameter adjustment unit 50 receives the retry information from the quantization statistic calculation unit 40, the parameter adjustment unit 50 inputs the encoding parameter for re-encoding to the encoding unit 20 as described above. As a result, the encoding unit 20 encodes the same GOP using an encoding parameter with a small generated code amount at the time of re-encoding.
- a process for encoding a certain GOP will be described in three cases as follows.
- a default encoding parameter is used, and filtering processing by the prefilter unit 21 is applied to a picture to be encoded with a prefilter strength corresponding to the default encoding parameter, and a DCT ( The Discrete Cosine Transform) coefficient is a quantization parameter according to the default encoding parameter, and is quantized by the quantization unit 22.
- DCT The Discrete Cosine Transform
- the quantization statistic calculation unit 40 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 20. In this example, since the quantization statistic does not exceed a predetermined threshold, the quantization statistic calculation unit 40 does not output retry information (S3). If the encoding target picture is the last picture in the input video signal, the output buffer 30 outputs the stored encoded stream, and the encoding process is completed (S4). Alternatively, if the encoding target picture is the last picture of the GOP, the output buffer 30 outputs the stored encoded stream, and the input buffer 10 discards the stored picture, and the first GOP The process proceeds to a picture encoding process (S5). Here, since re-encoding has not occurred in the GOP, the process proceeds to the encoding process of the first picture of the next GOP without changing the encoding parameter (S6).
- the quantization statistic calculation unit 40 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 20. As a result, when the quantization statistic calculation unit 40 detects that the quantization statistic exceeds a predetermined threshold for the picture, the quantization statistic calculation unit 40 includes the encoding unit 20 and the parameter adjustment unit 50. The retry information is output to the input buffer 10 and the output buffer 30 (S3).
- the input buffer 10 When retrying has not yet occurred for the GOP being encoded (S7), the input buffer 10 outputs the accumulated first picture of the GOP being encoded to the encoding unit 20 (S8), and parameter adjustment The unit 50 outputs the encoding parameter for re-encoding to the encoding unit 20 (S9). Further, the output buffer 30 discards the encoded stream of the GOP being encoded. Then, the encoding unit 20 encodes the leading picture of the input GOP using the re-encoding encoding parameter.
- the encoding parameter for re-encoding is used in encoding, and the pre-filter strength corresponding to the encoding parameter for re-encoding (the blurring degree is greater than the default encoding parameter) is applied to the picture to be encoded.
- a pre-filtering process by the filter unit 21 is applied.
- the DCT coefficient generated in this picture is quantized by the quantization unit 22 with a quantization parameter (a quantization step size larger than the default encoding parameter) according to the re-encoding encoding parameter.
- pictures of the GOP are sequentially input from the input buffer 10 to the encoding unit 20, and the encoding unit 20 performs encoding processing.
- the encoding of the last picture of the GOP is completed (S5)
- the encoded stream of the GOP is output from the output buffer 30, and the encoding unit 20 sets the encoding parameter as a default encoding parameter ( S6)
- the process proceeds to the next GOP encoding process.
- the operation when the encoding of the last picture of the input video is completed is the same as in the case 1 described above.
- Fig. 7 shows a conceptual diagram of changing the encoding parameters when re-encoding is performed.
- a re-encoding encoding parameter that suppresses the generated code amount is set, and GOP2 Are re-encoded from the first I picture.
- the encoding parameter for re-encoding is returned to the default encoding parameter in the next GOP3 encoding, and the encoding process is continued. ing.
- FIG. 8 shows a conceptual diagram of the transition of the remaining CPB code amount when re-encoding is performed.
- the portion indicated by the bold line is the CPB remaining code amount after re-encoding.
- the degree of blurring is increased by the pre-filter, and the quantization parameter is made larger than the default encoding parameter. Therefore, the generated code amount is suppressed, and the transition of the remaining CPB code amount is as shown in FIG. 8, for example. .
- the CPB residual code amount in a picture that has undergone re-encoding increases at the time of re-encoding and that the picture quality is greatly deteriorated in the picture.
- FIG. 9 shows a conceptual diagram of transition of quantization statistics when re-encoding is performed.
- the quantization statistic of the picture that has started re-encoding becomes large.
- the CPB residual code amount is increased as shown in FIG. Since there is a margin, the quantization statistic is smaller in the picture where re-encoding has occurred than before re-encoding.
- FIG. 10 shows a conceptual diagram of the transition of the quantization statistic when re-encoding is performed and it is not possible to avoid the quantization statistic exceeding the threshold even by re-encoding.
- Case 3 can occur, for example, as shown in FIG. 10, when the quantization statistics are already large at the head of the GOP at which re-encoding is started.
- the quantization statistic calculation unit 40 detects that the quantization statistic exceeds a predetermined threshold, and the operation for re-encoding the GOP is the same as in case 2. If the quantization statistic exceeds a predetermined threshold during the re-encoding of the GOP (S3, S7), the re-encoding is not performed and the encoding process is continued (the process proceeds to S4).
- the reference code RS10 indicates that the quantization statistic cannot be prevented from exceeding the threshold even after re-encoding.
- the quantization parameter becomes larger at the time of re-encoding than at the time of normal encoding, so that at the time of re-encoding, the quantization statistic of the past picture in the encoding order rather than the picture that triggered re-encoding May exceed the threshold.
- the quantization statistic threshold is modified to a value equal to the quantization statistic threshold. May be.
- the quantization during re-encoding Set the parameter value equal to the normal encoding value.
- FIG. 11 is a process flowchart showing the moving picture coding control method according to the present embodiment.
- a picture next to a picture that has been encoded in the input video signal is set as an encoding target (step S101).
- the input picture set as the encoding target is defined as H.264. H.264 and other predetermined encoding methods (step S102). It is determined whether or not the quantization statistic of the picture when the input picture is encoded exceeds a predetermined threshold (step S103). If the quantization statistic exceeds the predetermined threshold, the processing is performed. Proceed to step S108.
- step S104 it is determined whether or not the final picture has been encoded. If the quantization statistic does not exceed the predetermined threshold value, it is determined whether or not the final picture has been encoded (step S104). If the encoding is completed up to the final picture, the encoding process is terminated.
- step S105 it is determined whether encoding of the encoding order picture group has been completed. If the encoding order picture group has not been encoded, the process returns to step S101 to continue the encoding process for the next picture in the same manner.
- the retry count is 1 or more, the retry count is decreased by 1 (step S106). Note that the initial value of the retry count is zero.
- an encoding parameter predetermined according to the retry count is set (step S107), the process returns to step S101, and the encoding process starts from the first picture in the next encoding order picture group. I do.
- step S108 it is determined whether or not the current retry count value is a predetermined maximum value (step S108). If the retry count is the maximum value, no further re-encoding is performed, the process proceeds to step S104, and the encoding process is continued as it is.
- the first picture of the current encoding order picture group is set as an encoding target in order to re-encode the current encoding order picture group (step S109). Then, the retry count is increased by 1 (step S110). Then, based on the retry count, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (the quantization parameter changes the step size more greatly, and in the case of filter strength, the blurring degree is changed). (Changed more greatly) (step S111), the process returns to step S102 to re-encode the encoding order picture group being encoded.
- this embodiment is basically a single encoding process, and only when the re-encoding condition is satisfied, the encoding order picture group Each picture of (for example, GOP) is repeatedly encoded with the generated code amount being suppressed in stages until the re-encoding condition is not satisfied.
- encoding is performed with an encoding parameter that suppresses the generated code amount determined according to the retry count. Therefore, it is possible to reduce the amount of calculation compared to the conventional technique b in which all the pictures of the input video are encoded twice, and it is possible to reduce deterioration in image quality due to re-encoding.
- the encoding parameter is changed according to the retry count at the time of re-encoding.
- a pre-filter is applied to the input video during encoding, and the encoding parameters to be changed are a quantization parameter and a pre-filter strength. Both of these two encoding parameters may be changed, or only one of them may be changed.
- a predetermined offset value that increases stepwise according to the retry count is added to the quantization parameter value determined during normal encoding, and re-encoding is performed with a larger quantization parameter.
- a Gaussian filter is used in this embodiment.
- the Gaussian filter can be created by sampling a Gaussian distribution represented by the following equation with respect to x and y.
- g (x, y) ⁇ 1 / (2 ⁇ 2 ) ⁇ ⁇ exp ⁇ (x 2 + y 2 ) / (2 ⁇ 2 ) ⁇
- the greater the value of ⁇ the greater the degree of blurring.
- the degree of blurring increases, the high frequency components decrease, and the amount of generated code during encoding decreases. Details of the Gaussian filter are described in Non-Patent Document 2 described above, for example.
- the Gaussian filter is not applied.
- the type of the low pass filter is not limited.
- the default encoding parameter ⁇ 0 may be changed according to the complexity of each picture, and ⁇ c may be obtained by adding a predetermined offset to ⁇ c ⁇ 1 .
- quantization statistics in this embodiment, an average value of quantization parameters of each macroblock of a picture is used.
- the encoding method is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP.
- a conceptual diagram of the GOP at the time of encoding is as shown in FIG.
- One GOP is composed of 10 pictures, and B pictures and P pictures are alternately arranged with the I picture at the head in the display order.
- FIG. 12 shows an apparatus configuration example of this embodiment.
- the input buffer 110 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 120. Further, when the input buffer 110 receives information (retry information) indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 140 described later, The video signal is output again to the encoding unit 120 from the first picture of the GOP being encoded. When the GOP encoding is completed without receiving the retry information, the input buffer 110 discards the stored video signal of the GOP.
- retry information information indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 140 described later
- the encoding unit 120 encodes the video signal input from the input buffer 110 and outputs the encoded stream to the output buffer 130. Further, the encoding unit 120 outputs the quantization parameter (quantization parameter information) of each macroblock when the input video signal is encoded to the quantization statistic calculation unit 140. Furthermore, when receiving the retry information from the quantization statistic calculation unit 140, the encoding unit 120 receives the video signal from the first picture of the GOP being encoded again from the input buffer 110 and also sets the parameter adjustment unit 160. Since the encoding parameter for re-encoding is input from, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 130 outputs the encoded stream of the GOP when all the encoded streams of the GOP are accumulated. On the other hand, when receiving the retry information from the quantization statistic calculation unit 140, the output buffer 130 The encoded stream accumulated for the GOP is discarded.
- the quantization statistic calculation unit 140 uses the quantization parameter information input from the encoding unit 120 to obtain a quantization statistic that changes in units of pictures. When the quantization statistic exceeds a predetermined threshold, the quantization statistic calculation unit 140 outputs retry information to the input buffer 110, the encoding unit 120, the retry count management unit 150, and the output buffer 130, That the statistic has exceeded a predetermined threshold.
- the parameter adjustment unit 160 When the parameter adjustment unit 160 receives the retry count from the retry count management unit 150, the parameter adjustment unit 160 inputs an encoding parameter determined according to the retry count to the encoding unit 120. As a result, the encoding unit 120 performs encoding using an encoding parameter in which the generated code amount decreases as the number of repetitions of re-encoding increases for the same GOP.
- the retry count management unit 150 introduces the concept of retry count that increases when re-encoding occurs and decreases when GOP encoding is completed. Manage counts.
- the retry count has a predetermined upper limit value, for example, an upper limit value of “3”, and the same GOP may be re-encoded until the upper limit value is reached.
- the offset value of the quantization parameter at the time of encoding and the filter strength of the pre-filter change according to the retry count value.
- re-encoding encoding parameters corresponding to the retry counts 1, 2, and 3 are prepared in advance as an encoding parameter table. Then, the encoding parameter obtained from the encoding parameter table may be used for re-encoding.
- a process for encoding a certain GOP will be described in three cases as follows.
- the prefilter unit 121 applies the encoding target picture with the prefilter strength corresponding to the default encoding parameter.
- a filtering process is applied.
- the DCT coefficient generated in this picture is quantized by the quantization unit 122 with a quantization parameter according to the default encoding parameter.
- the retry count is 1 or more, encoding is performed by pre-filtering and quantization processing based on the filter strength and the quantization parameter determined according to the retry count.
- the quantization statistic calculation unit 140 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 120. In this example, since the quantization statistic does not exceed a predetermined threshold, the quantization statistic calculation unit 140 does not output retry information (S103). If the encoding target picture is the last picture in the input video signal, the output buffer 130 outputs the stored encoded stream, and the encoding process is completed (S104). Alternatively, if the encoding target picture is the last picture of the GOP, the output buffer 130 outputs the stored encoded stream, and the input buffer 110 discards the stored picture, and the first GOP of the next GOP is output. The process proceeds to picture coding processing (S105 to S107).
- the retry count management unit 150 determines whether the retry count is 0, except when the retry count is 0. The value is decremented by 1 from the retry count (S106). The retry count may not be zero when re-encoding occurs in a GOP prior to the GOP that has currently been encoded. The retry count management unit 150 notifies the parameter adjustment unit 160 of the retry count after the change, and the parameter adjustment unit 160 sets the encoding parameter corresponding to the notified retry count in the encoding unit 120 and sets the next GOP. Encoding of the first picture is started.
- Case 2 will be described in which the quantization statistic exceeds a predetermined threshold value a plurality of times in GOP encoding, but the quantization statistic can be prevented from exceeding the threshold value by re-encoding.
- a case will be described in which the retry count at the start of GOP encoding is 1, and re-encoding is performed twice with the same GOP.
- the input buffer 110 stores the picture and inputs the picture to the encoding unit 120 as an encoding target picture (S101). Then, the encoding unit 120 encodes the picture, outputs the encoded stream to the output buffer 130 (the output buffer 130 does not output the encoded stream and stores the encoded stream), and stores quantization parameter information regarding the picture. It outputs to the quantization statistic calculation part 140 (S102).
- an encoding parameter corresponding to retry count 1 is used.
- the quantization statistic calculation unit 140 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 120. As a result, when the quantization statistic calculation unit 140 detects that the quantization statistic exceeds a predetermined threshold for the picture, the quantization statistic calculation unit 140 includes the encoding unit 120 and the retry count management unit. 150, the retry information is output to the input buffer 110 and the output buffer 130 (S103).
- the input buffer 110 Since the current retry count is 1 and has not reached the upper limit of 3 (S108), the input buffer 110 outputs the accumulated first picture of the GOP being encoded to the encoding unit 120 (S109). ). On the other hand, the retry count is incremented by 1 in the retry count management unit 150, and the retry count having a value of 2 is output to the parameter adjustment unit 160 (S110).
- the parameter adjustment unit 160 reads the encoding parameter when the retry count is 2 from the encoding parameter table, and sets the encoding parameter in the encoding unit 120 (S111).
- the output buffer 130 discards the encoded stream of the GOP being encoded.
- the retry count management unit 150 decrements the retry count by 1, and the retry count becomes 2, so that the code of the next GOP Will be promoted.
- the operations of the input buffer 110 and the output buffer 130 at this time are the same as in the above-described example.
- FIG. 13 shows a conceptual diagram of retry count and coding parameter transition in the case 2 example.
- the quantization statistic exceeds a predetermined threshold in the encoding of the sixth picture, so the retry count is 2
- the quantization statistic does not exceed the predetermined threshold value. Therefore, when the GOP2 encoding is completed, 1 is subtracted from the retry count, and the encoding parameter with the retry count of 2 is used. Processing has shifted to GOP3 encoding.
- the conceptual diagram of the transition of the CPB residual code amount when re-encoding is performed is as shown in FIG.
- the portion indicated by the bold line is the CPB remaining code amount after re-encoding.
- the degree of blurring is increased by the pre-filter, and the quantization parameter is made larger than the default encoding parameter. Therefore, the generated code amount is suppressed, and the transition of the remaining CPB code amount is as shown in FIG. 8, for example. .
- the CPB residual code amount in a picture that has undergone re-encoding increases at the time of re-encoding and that the picture quality is greatly deteriorated in the picture.
- the conceptual diagram of the transition of the quantization statistics when re-encoding is performed is as shown in FIG.
- the quantization statistic of the picture that has started re-encoding becomes large.
- the CPB residual code amount is increased as shown in FIG. Since there is a margin, the quantization statistic is smaller in the picture where re-encoding has occurred than before re-encoding.
- the retry count management unit 150 sets the retry count to the upper limit value. It is detected that this has been reached (S108), and the encoding process proceeds without re-encoding.
- FIG. Case 3 The conceptual diagram of the transition of the quantization statistic when re-encoding is performed and it cannot be avoided that the quantization statistic exceeds the threshold even by re-encoding is as shown in FIG. Case 3 can occur, for example, as shown in FIG. 10, when the quantization statistics are already large at the head of the GOP at which re-encoding is started.
- the quantization parameter becomes larger at the time of re-encoding than at the time of normal encoding, so that at the time of re-encoding, the quantization statistic of the past picture in the encoding order rather than the picture that triggered re-encoding May exceed the threshold.
- the offset value of the quantization parameter corresponding to each value of the retry count may be determined as follows.
- the quantization parameter offset value (this is a predetermined value) corresponding to the maximum value of the retry count (3 in the above embodiment) is added to the quantization parameter at the time of normal encoding, and the value is quantized.
- the threshold value of the quantization statistic is exceeded, the offset value of the quantization parameter corresponding to the maximum value of the retry count is corrected so that the value is equal to the threshold value.
- an offset value corresponding to another retry count value is determined (for example, in the case of the above-described embodiment, when the offset value corresponding to the maximum retry count value is A).
- the offset values of the retry counts 0, 1, and 2 may be equally divided into 0, A / 3, 2 ⁇ (A / 3), respectively.
- FIG. 14 is a process flowchart showing the moving picture coding control method according to the present embodiment.
- a picture next to a picture that has been encoded in the input video signal is set as an encoding target (step S201).
- the input picture set as the encoding target is defined as H.264. H.264 and other predetermined encoding methods (step S202). It is determined whether or not the quantization statistic of the picture when the input picture is encoded exceeds a predetermined threshold (step S203), and if the quantization statistic exceeds the predetermined threshold, the processing is performed. Proceed to step S208.
- step S204 it is determined whether or not the final picture has been encoded. If the quantization statistic does not exceed the predetermined threshold value, it is determined whether or not the final picture has been encoded (step S204). If the encoding is completed up to the final picture, the encoding process is terminated.
- step S205 it is determined whether encoding of the encoding order picture group has been completed. If the encoding order picture group has not been encoded, the process returns to step S201, and the encoding process is continued in the same manner for the next picture.
- step S206 When encoding of the encoding-order picture group is completed, it is determined whether the following condition is satisfied, and the retry count is decreased by 1 only when the condition is satisfied (step S206).
- -Condition 1 Retry count is 1 or more.
- Condition 2 CPB residual code amount is not less than a predetermined threshold. When the retry count is 0, or when the remaining CPB code amount is smaller than a predetermined threshold, the retry count is not decreased and remains unchanged.
- step S207 an encoding parameter predetermined according to the retry count is set (step S207), the process returns to step S201, and the encoding process starts from the first picture in the next encoding order picture group. I do.
- step S208 If it is detected in step S203 that the quantization statistic exceeds a predetermined threshold value, it is determined whether the current retry count value is a predetermined maximum value (step S208). If the retry count is the maximum value, re-encoding is not performed, and the process proceeds to step S204, where the encoding process is continued.
- the first picture of the current encoding order picture group is set as an encoding target in order to re-encode the current encoding order picture group (step S209). Then, the retry count is increased by 1 (step S210). Then, based on the retry count, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (the quantization parameter changes the step size more greatly, and in the case of filter strength, the blurring degree is changed). (Changed more greatly) (step S211), the process returns to step S202, and the encoding order picture group being encoded is re-encoded.
- quantization parameter quantization parameter changes the step size more greatly, and in the case of filter strength, the blurring degree is changed.
- this embodiment is basically a single encoding process, and only when the re-encoding condition is satisfied, the encoding order picture group Each picture of (for example, GOP) is repeatedly encoded with the generated code amount being suppressed in stages until the re-encoding condition is not satisfied.
- encoding is performed with an encoding parameter that suppresses the generated code amount determined according to the retry count. Therefore, it is possible to reduce the amount of calculation compared to the conventional technique b in which all the pictures of the input video are encoded twice, and it is possible to reduce deterioration in image quality due to re-encoding.
- the encoding parameter is changed according to the retry count at the time of re-encoding.
- a pre-filter is applied to the input video during encoding, and the encoding parameters to be changed are a quantization parameter and a pre-filter strength. Both of these two encoding parameters may be changed, or only one of them may be changed.
- a predetermined offset value that increases stepwise according to the retry count is added to the quantization parameter value determined during normal encoding, and re-encoding is performed with a larger quantization parameter.
- a Gaussian filter is used in this embodiment.
- the Gaussian filter can be created by sampling a Gaussian distribution represented by the following equation with respect to x and y.
- g (x, y) ⁇ 1 / (2 ⁇ 2 ) ⁇ ⁇ exp ⁇ (x 2 + y 2 ) / (2 ⁇ 2 ) ⁇
- the greater the value of ⁇ the greater the degree of blurring.
- the degree of blurring increases, the high frequency components decrease, and the amount of generated code during encoding decreases. Details of the Gaussian filter are described in Non-Patent Document 2 described above, for example.
- the Gaussian filter is not applied.
- the type of the low pass filter is not limited.
- the default encoding parameter ⁇ 0 may be changed according to the complexity of each picture, and ⁇ c may be obtained by adding a predetermined offset to ⁇ c ⁇ 1 .
- quantization statistics in this embodiment, an average value of quantization parameters of each macroblock of a picture is used.
- the encoding method is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP.
- a conceptual diagram of the GOP at the time of encoding is as shown in FIG.
- One GOP is composed of 10 pictures, and B pictures and P pictures are alternately arranged with the I picture at the head in the display order.
- FIG. 15 shows an example of the apparatus configuration of this embodiment.
- the input buffer 210 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 220. Further, when the input buffer 210 receives information (retry information) indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 240 described later, The video signal is output again to the encoding unit 220 from the first picture of the GOP being encoded. When the GOP encoding is completed without receiving retry information, the input buffer 210 discards the stored video signal of the GOP.
- retry information information indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 240 described later
- the encoding unit 220 encodes the video signal input from the input buffer 210 and outputs the encoded stream to the output buffer 230. Also, the encoding unit 220 outputs the quantization parameter (quantization parameter information) of each macroblock when the input video signal is encoded to the quantization statistic calculation unit 240. Also, the encoding unit 220 notifies the CPB state prediction unit 260 of the CPB remaining code amount information when the GOP encoding is completed.
- the encoding unit 220 receives the video signal from the first picture of the GOP being encoded again from the input buffer 210 and also sets the parameter adjustment unit 270. Since the encoding parameter for re-encoding is input from, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 230 outputs the encoded stream of the GOP when all the encoded streams of the GOP are accumulated. On the other hand, when receiving the retry information from the quantization statistic calculation unit 240, the output buffer 230 The encoded stream accumulated for the GOP is discarded.
- the quantization statistic calculation unit 240 uses the quantization parameter information input from the encoding unit 220 to obtain a quantization statistic that changes in units of pictures. When the quantization statistic exceeds a predetermined threshold, the quantization statistic calculation unit 240 outputs retry information to the input buffer 210, the encoding unit 220, the retry count management unit 250, and the output buffer 230, That the statistic has exceeded a predetermined threshold.
- the retry count management unit 250 When the retry count management unit 250 receives the retry information from the quantization statistic calculation unit 240, the retry count management unit 250 adds 1 to the current retry count value and notifies the parameter adjustment unit 270 of the updated retry count. In addition, when the GOP being encoded is completed without receiving retry information from the quantization statistic calculation unit 240, if the retry count value is 1 or more, the retry count management unit 250 sets the retry count. 1 is subtracted from the count value, and the updated retry count is notified to the parameter adjustment unit 270.
- the retry count management unit 250 subtracts 1 from the retry count even if the retry count is 1 or more. do not do. Even when the retry count is 0, the retry count management unit 250 notifies the parameter adjustment unit 270 of the current retry count value without subtracting 1 from the retry count.
- the CPB state prediction unit 260 determines whether the CPB residual code amount is equal to or greater than a predetermined threshold based on the CPB residual code amount information notified from the encoding unit 220 when the GOP encoding is completed, When the CPB remaining code amount is equal to or larger than the threshold, the retry count management unit 250 is notified that the encoding parameter is changed as parameter change presence / absence information. On the other hand, when the CPB remaining code amount is smaller than the threshold, the CPB state prediction unit 260 notifies the retry count management unit 250 that the coding parameter is not changed as the parameter change presence / absence information.
- the parameter adjustment unit 270 When the parameter adjustment unit 270 receives the retry count from the retry count management unit 250, the parameter adjustment unit 270 inputs an encoding parameter determined according to the retry count to the encoding unit 220. As a result, the encoding unit 220 performs encoding using an encoding parameter that reduces the generated code amount as the number of repetitions of re-encoding increases for the same GOP.
- the retry count management unit 250 introduces the concept of a retry count that increases when re-encoding occurs and decreases when GOP encoding is completed. Manage counts.
- the retry count has a predetermined upper limit value, for example, an upper limit value of “3”, and the same GOP may be re-encoded until the upper limit value is reached.
- the offset value of the quantization parameter at the time of encoding and the filter strength of the pre-filter change according to the retry count value.
- re-encoding encoding parameters corresponding to the retry counts 1, 2, and 3 are prepared in advance as an encoding parameter table. Then, the encoding parameter obtained from the encoding parameter table may be used for re-encoding.
- a process for encoding a certain GOP will be described in three cases as follows.
- the prefilter unit 221 applies the encoding target picture with the prefilter strength corresponding to the default encoding parameter.
- a filtering process is applied.
- the DCT coefficient generated in this picture is quantized by the quantization unit 222 with a quantization parameter according to the default encoding parameter.
- the retry count is 1 or more, encoding is performed by pre-filtering and quantization processing based on the filter strength and the quantization parameter determined according to the retry count.
- the quantization statistic calculation unit 240 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 220. In this example, since the quantization statistic does not exceed a predetermined threshold, the quantization statistic calculation unit 240 does not output retry information (S203). If the encoding target picture is the last picture in the input video signal, the output buffer 230 outputs the stored encoded stream, and the encoding process is completed (S204). Alternatively, if the encoding target picture is the last picture of the GOP, the output buffer 230 outputs the stored encoded stream, and the input buffer 210 discards the stored picture, and the first GOP of the next GOP is output. The process proceeds to picture coding processing (S205 to S207).
- the encoding unit 220 when the GOP encoding is completed without the quantization statistic exceeding the predetermined threshold, the encoding unit 220, when the GOP encoding is completed, the CPB residual code amount information Is notified to the CPB state prediction unit 260.
- the CPB state prediction unit 260 determines whether or not the CPB residual code amount is equal to or larger than a predetermined threshold. If the CPB residual code amount is equal to or larger than the threshold, the retry count management unit changes the coding parameter as parameter change presence / absence information. 250 is notified. On the other hand, when the CPB remaining code amount is smaller than the threshold value, the retry count management unit 250 is notified that the coding parameter is not changed as the parameter change presence / absence information. The retry count management unit 250 decrements the value from the current retry count by 1 only when the parameter change presence / absence information indicates that the encoding parameter is to be changed (S206).
- the retry count may not be 0 when re-encoding occurs in a GOP before the GOP that has been encoded.
- the retry count management unit 250 changes the retry count according to the notification of the parameter change presence / absence information from the CPB state prediction unit 260 and notifies the parameter adjustment unit 270 of the changed retry count.
- the parameter adjustment unit 270 sets the encoding parameter corresponding to the notified retry count in the encoding unit 220, and starts encoding the first picture of the next GOP.
- Case 2 will be described in which the quantization statistic exceeds a predetermined threshold value a plurality of times in GOP encoding, but the quantization statistic can be prevented from exceeding the threshold value by re-encoding.
- a case will be described in which the retry count at the start of GOP encoding is 1, and re-encoding is performed twice with the same GOP.
- the input buffer 210 stores the picture and inputs the picture to the encoding unit 220 as an encoding target picture (S201). Then, the encoding unit 220 encodes the picture, outputs the encoded stream to the output buffer 230 (the output buffer 230 does not output the encoded stream and accumulates it), and stores quantization parameter information regarding the picture. It outputs to the quantization statistic calculation part 240 (S202).
- an encoding parameter corresponding to retry count 1 is used.
- the quantization statistic calculation unit 240 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 220. As a result, when the quantization statistic calculation unit 240 detects that the quantization statistic exceeds the predetermined threshold for the picture, the quantization statistic calculation unit 240 includes the encoding unit 220 and the retry count management unit. 250, the retry information is output to the input buffer 210 and the output buffer 230 (S203).
- the input buffer 210 Since the current retry count is 1 and has not reached the upper limit of 3 (S208), the input buffer 210 outputs the accumulated first picture of the GOP being encoded to the encoding unit 220 (S209). ). On the other hand, the retry count is incremented by 1 in the retry count management unit 250, and the retry count having a value of 2 is output to the parameter adjustment unit 270 (S210).
- the parameter adjustment unit 270 reads the encoding parameter when the retry count is 2 from the encoding parameter table, and sets the encoding parameter in the encoding unit 220 (S211).
- the output buffer 230 discards the encoded stream of the GOP being encoded.
- the encoding unit 220 unless the quantization statistic exceeds a predetermined threshold, GOP pictures are sequentially input from the input buffer 210, and encoding proceeds.
- the quantization statistic exceeds the predetermined threshold again with the same GOP, the retry count is incremented by 1 and becomes 3 by the same process as described above.
- the encoding unit 220 when the quantization statistic does not exceed the predetermined threshold any more, the encoding unit 220 notifies the CPB state prediction unit 260 of the CPB remaining code amount information.
- the CPB state prediction unit 260 sets the parameter change presence / absence information as “changed” when the CPB residual code amount is equal to or greater than a predetermined threshold, and sets the parameter change presence / absence information as “no change” otherwise. Notification to the unit 250.
- the retry count is reduced by 1 by the retry count management unit 250, the retry count becomes 2, and encoding of the next GOP proceeds.
- the operations of the input buffer 210 and the output buffer 230 at this time are the same as in the above-described example. If the parameter change presence / absence information is “no change”, the retry count remains 3, and the encoding of the next GOP proceeds.
- the conceptual diagram of the retry count and the encoding parameter transition in the case 2 example is as shown in FIG.
- the quantization statistic does not exceed the predetermined threshold, it is determined whether the CPB remaining code amount is equal to or larger than the predetermined threshold.
- the CPB remaining code amount is equal to or greater than a predetermined threshold, 1 is subtracted from the retry count when the GOP2 encoding is completed, and the next GOP3 encoding is processed using an encoding parameter with a retry count of 2. Has migrated.
- the conceptual diagram of the transition of the CPB residual code amount when re-encoding is performed is as shown in FIG.
- the portion indicated by the bold line is the CPB remaining code amount after re-encoding.
- the degree of blurring is increased by the pre-filter, and the quantization parameter is made larger than the default encoding parameter. Therefore, the generated code amount is suppressed, and the transition of the remaining CPB code amount is as shown in FIG. 8, for example. .
- the CPB residual code amount in a picture that has undergone re-encoding increases at the time of re-encoding and that the picture quality is greatly deteriorated in the picture.
- the conceptual diagram of the transition of the quantization statistics when re-encoding is performed is as shown in FIG.
- the quantization statistic of the picture that has started re-encoding becomes large.
- the CPB residual code amount is increased as shown in FIG. Since there is a margin, the quantization statistic is smaller in the picture where re-encoding has occurred than before re-encoding.
- the retry count management unit 250 sets the retry count to the upper limit value. It is detected that this has been reached (S208), and the encoding process proceeds without re-encoding.
- FIG. Case 3 The conceptual diagram of the transition of the quantization statistic when re-encoding is performed and it cannot be avoided that the quantization statistic exceeds the threshold even by re-encoding is as shown in FIG. Case 3 can occur, for example, as shown in FIG. 10, when the quantization statistics are already large at the head of the GOP at which re-encoding is started.
- the quantization parameter becomes larger at the time of re-encoding than at the time of normal encoding, so that at the time of re-encoding, the quantization statistic of the past picture in the encoding order rather than the picture that triggered re-encoding May exceed the threshold.
- the offset value of the quantization parameter corresponding to each value of the retry count may be determined as follows.
- the quantization parameter offset value (this is a predetermined value) corresponding to the maximum value of the retry count (3 in the above embodiment) is added to the quantization parameter at the time of normal encoding, and the value is quantized.
- the threshold value of the quantization statistic is exceeded, the offset value of the quantization parameter corresponding to the maximum value of the retry count is corrected so that the value is equal to the threshold value.
- an offset value corresponding to another retry count value is determined (for example, in the case of the above-described embodiment, when the offset value corresponding to the maximum retry count value is A).
- the offset values of the retry counts 0, 1, and 2 may be equally divided into 0, A / 3, 2 ⁇ (A / 3), respectively.
- FIG. 16 is a process flowchart showing the moving picture coding control method according to the present embodiment.
- a picture next to a picture that has been encoded in the input video signal is set as an encoding target (step S301).
- the input picture set as the encoding target is defined as H.264.
- H.264 or other predetermined encoding methods are used (step S302). It is determined whether or not the quantization statistic of the picture when the input picture is encoded exceeds a predetermined threshold (step S303), and if the quantization statistic exceeds the predetermined threshold, the processing is performed. The process proceeds to step S311.
- step S304 it is determined whether or not the final picture has been encoded. If the quantization statistic does not exceed the predetermined threshold value, it is determined whether or not the final picture has been encoded (step S304). If the encoding is completed up to the final picture, the encoding process is terminated.
- step S305 it is determined whether the encoded picture is the first I picture in the encoding order picture group. If the current encoded picture is the first I picture in the encoding order picture group, the I picture is set as a retry point (step S306). This is because, in step S309, which will be described later, when the CPB residual code amount is less than the predetermined threshold value, the retry point remains set at the head of the previous coding-order picture group, so that the next I picture is reproduced again. This is a process for updating the retry point after confirming that the encoding condition (quantization statistic exceeds a predetermined threshold) is not satisfied. If a retry point is set in step S310, the retry point is reset at the same position, but there is no inconvenience in processing. Thereafter, the process returns to step S301 to proceed with encoding of the next picture.
- step S307 it is next determined whether or not the encoding order picture group has been encoded. If the encoding order picture group has not been encoded, the process returns to step S301, and the encoding process is continued in the same manner for the next picture.
- the encoding parameter is changed by re-encoding (retry) of the encoding order picture group, the encoding parameter is returned to the value at the time of normal encoding (Ste S308).
- step S309 it is determined whether or not the CPB remaining code amount is equal to or larger than a predetermined threshold. If the CPB remaining code amount is equal to or larger than the predetermined threshold, the retry point is set to the first I picture of the next coding order picture group (step S310). Thereafter, the processing returns to step S301, and encoding is performed in order from the beginning of the next encoding order picture group.
- the retry point is not updated, and the process returns to step S301 to proceed to the encoding of the next encoding order picture group.
- step S303 If it is detected in step S303 that the quantization statistic exceeds a predetermined threshold, it is determined whether or not the current coding-order picture group has been re-encoded (retry has been completed) (step S311). ). If the retry has been completed, no further re-encoding is performed, the process proceeds to step S304, and the encoding process is continued as it is.
- step S312 If it has not been retried, the picture at the retry point is set as an encoding target in order to re-encode the current encoding order picture group (step S312). Then, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (the quantization parameter changes the step size more greatly, and in the case of the filter strength, the blurring degree changes more greatly) ( In step S313), the process returns to step S302 to re-encode the encoding order picture group being encoded.
- the two encoding parameters quantization parameter, prefilter strength
- the encoding order picture group (for example, GOP) is encoded twice only when the quantization statistic exceeds a predetermined threshold.
- encoding is performed with an encoding parameter that suppresses the generated code amount. Only when the re-encoding condition is satisfied, only the encoding order picture group in which it is satisfied can be re-encoded (except that the previous encoding order picture group may be re-encoded. Yes), image quality deterioration is reduced while suppressing CPB underflow. Therefore, the amount of calculation can be reduced as compared with the conventional technique b in which all the pictures of the input video are encoded twice.
- FIG. 17 is a process flowchart showing a video encoding control method according to a modification of the present embodiment.
- the process of step S308 shown in FIG. 16 may be replaced with the processes of steps S381 to S383 shown in FIG. Processes other than step S308 are substantially the same as those in FIG.
- step S381 it is determined whether the encoding parameter has been changed by retry. If the encoding parameter has not been changed by retry, the process proceeds to step S309. If the coding parameter has been changed by retry, it is next determined whether or not the remaining CPB code amount is equal to or greater than a predetermined first threshold (step S382). If the CPB residual code amount is less than the predetermined threshold value, the encoding parameter remains in the state used for re-encoding, and the encoding parameter is restored to the original default encoding only when the CPB residual code amount is equal to or larger than the predetermined threshold value. The parameters are returned (step S383).
- step S309 it is determined whether or not the CPB residual code amount is equal to or larger than a predetermined second threshold.
- This process and the process of step S310 are the same as the processes of steps S309 and S310 shown in FIG. is there. Note that the first threshold value and the second threshold value may be the same value or different values.
- the encoding parameter is set at the time of normal encoding. Return to value. This is due to the following reason. Even if encoding of the encoding order picture group is completed, if the CPB residual code amount is small, the generated encoding amount increases when the encoding parameter is returned to the value at the time of normal encoding. The possibility that the re-encoding condition is satisfied by encoding the pictures of the group of pictures increases. In the process of FIG. 17, when the CPB residual code amount is small, the encoding parameter is not changed. Therefore, compared with the process of FIG. 16, the occurrence of re-encoding in the encoding of the next encoding order picture group is suppressed. As a result, the amount of calculation is further reduced.
- the encoding parameter is changed during re-encoding.
- a pre-filter is applied to the input video during encoding, and the encoding parameters to be changed are a quantization parameter and a pre-filter strength. Both of these two encoding parameters may be changed, or only one of them may be changed.
- Quantization parameters are re-encoded with a larger quantization parameter by adding a predetermined offset value to the quantization parameter value during normal encoding.
- a Gaussian filter is used in this embodiment.
- the Gaussian filter can be created by sampling a Gaussian distribution represented by the following equation with respect to x and y.
- g (x, y) ⁇ 1 / (2 ⁇ 2 ) ⁇ ⁇ exp ⁇ (x 2 + y 2 ) / (2 ⁇ 2 ) ⁇
- the greater the value of ⁇ the greater the degree of blurring.
- the degree of blurring increases, the high frequency components decrease, and the amount of generated code during encoding decreases. Details of the Gaussian filter are described in Non-Patent Document 2 described above, for example.
- the Gaussian filter is not applied.
- the type of the low pass filter is not limited.
- how to increase the degree of blurring during re-encoding may be arbitrarily determined in advance.
- the default encoding parameter ⁇ 0 may be changed in accordance with the complexity of each picture, and ⁇ 1 may be a value obtained by adding a predetermined offset to ⁇ 0 .
- quantization statistics in this embodiment, an average value of quantization parameters of each macroblock of a picture is used.
- Encoding is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP.
- a conceptual diagram of the GOP at the time of encoding is as shown in FIG.
- One GOP is composed of 10 pictures, and B pictures and P pictures are alternately arranged with the I picture at the head in the display order.
- FIG. 18 shows an example of the apparatus configuration of this embodiment.
- the input buffer 310 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 320. Further, when the input buffer 310 receives information (retry information) indicating that re-encoding is performed because the quantization statistic of the picture has exceeded a predetermined threshold from the quantization statistic calculation unit 340 described later, The video signal is output again to the encoding unit 320 from the first picture of the GOP set as the retry point. Further, when retry point information is input from the retry point management unit 360, the input buffer 310 discards the stored video signal of the GOP before the retry point.
- retry information information
- the encoding unit 320 encodes the video signal input from the input buffer 310 and outputs the encoded stream to the output buffer 330. Also, the encoding unit 320 outputs the quantization parameter (quantization parameter information) generated when the input video signal is encoded to the quantization statistic calculation unit 340. Furthermore, when receiving the retry information from the quantization statistic calculation unit 340, the encoding unit 320 receives the video signal from the first picture of the GOP indicated by the retry point from the input buffer 310 again, and the parameter adjustment unit 370. Since the encoding parameter for re-encoding is input from, re-encoding is performed using the input encoding parameter for re-encoding. Also, the encoding unit 320 outputs information on the CPB remaining code amount at the time when the GOP encoding is completed to the CPB state prediction unit 350.
- the output buffer 330 Based on the retry point information from the retry point management unit 360, the output buffer 330 outputs an encoded stream that is determined to be output, that is, an encoded stream that is determined to be unnecessary to be re-encoded. . On the other hand, when receiving the retry information from the quantization statistic calculation unit 340, the output buffer 330 discards the encoded stream accumulated for the GOP being encoded.
- the quantization statistic calculation unit 340 uses the quantization parameter information input from the encoding unit 320 to obtain a quantization statistic that changes in units of pictures. When the quantization statistic exceeds a predetermined threshold, the quantization statistic calculation unit 340 outputs the retry information to the input buffer 310, the encoding unit 320, the parameter adjustment unit 370, and the output buffer 330, and performs quantization. Notify that the statistic exceeds a predetermined threshold.
- the CPB state prediction unit 350 determines whether or not the CPB residual code amount is equal to or larger than a predetermined threshold. If the CPB residual code amount is equal to or larger than the threshold, the retry point management unit 360 determines the retry point of the next GOP. Information indicating the first I picture of the GOP is notified as retry point change presence / absence information. Conversely, when the CPB remaining code amount is smaller than the threshold, the CPB state prediction unit 350 indicates that the retry point of the first picture of the next GOP is the first picture (I picture) of the GOP immediately before the GOP. Information is notified to the retry point management unit 360 as retry point change presence / absence information.
- the retry point management unit 360 When the retry change presence / absence information indicates that the retry point is the first picture of the immediately preceding GOP in the first picture of the GOP to be encoded, the retry point management unit 360 notifies the input buffer 310 of the retry point. When the re-encoding does not occur in the encoding of the first picture, the input buffer 310 is notified that the retry point becomes the first picture of the GOP currently encoded from the encoding of the next picture. When the retry change presence / absence information indicates that the retry point is the first picture of the GOP to be encoded, the retry point management unit 360 notifies the input buffer 310 and the output buffer 330 of the retry point.
- notification information is referred to as retry point information.
- the input buffer 310 inputs the video signal from the picture based on the retry point information to the encoding unit 320 at the time of re-encoding, and the output buffer 330 is determined to be output based on the retry point information. Output only stream.
- the parameter adjustment unit 370 When the parameter adjustment unit 370 receives retry information from the quantization statistic calculation unit 340, the parameter adjustment unit 370 inputs the encoding parameter for re-encoding to the encoding unit 320 as described above. As a result, the encoding unit 320 encodes the same GOP using an encoding parameter with a small generated code amount at the time of re-encoding.
- a process for encoding a certain GOP will be described with the first GOP as GOP 1 and the next GOP as GOP 2 in the following four cases.
- the filtering process by the prefilter unit 321 is applied to the encoding target picture with the prefilter strength corresponding to the default encoding parameters.
- the DCT coefficient generated in this picture is quantized by the quantization unit 322 with a quantization parameter according to the default encoding parameter.
- the quantization statistic calculation unit 340 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 320. In this example, since the quantization statistic does not exceed a predetermined threshold, the quantization statistic calculation unit 340 does not output retry information (S303). If the encoding target picture is the last picture in the input video signal, the output buffer 330 outputs the stored encoded stream, and the encoding process is completed (S304).
- the retry point management unit 360 sets the first picture (I picture) of GOP1 as a retry point (S306), and the encoding unit 320 then The encoding of the picture is advanced.
- the parameter adjustment unit 370 encodes the encoding parameter by default encoding when the encoding parameter for re-encoding is used in re-encoding.
- the parameter is changed (S308).
- the encoding unit 320 outputs the CPB remaining code amount information to the CPB state prediction unit 350, and the CPB state prediction unit 350 determines whether the CPB remaining code amount is equal to or greater than a predetermined threshold (S309).
- the CPB state prediction unit 350 notifies the retry point management unit 360 of the determination result as the above-described retry point change presence / absence information.
- the retry point management unit 360 indicates in the input buffer 310 that the retry point is the first picture of GOP1. Notify as.
- the process proceeds to the encoding process of the first I picture of GOP2 (S302).
- the quantization statistic does not exceed a predetermined threshold in the encoding of the I picture (S303)
- the retry point management unit 360 Notifies the input buffer 310 and the output buffer 330 that the retry point is the first picture of GOP2 (S306). That is, when re-encoding occurs in subsequent GOP2 pictures, re-encoding is performed from the first picture of GOP2.
- retry point change presence / absence information indicating that the retry point is changed is sent from the CPB state prediction unit 350 to the retry point management unit 360. Then, the retry point management unit 360 notifies the input buffer 310 that the retry point is the first picture of GOP2 as retry point information (S310). In this case, re-encoding is performed from the first picture of GOP2 even if the quantization statistic exceeds the predetermined threshold in any picture of GOP2.
- the input buffer 310 sequentially inputs pictures to the encoding unit 320 from the first picture of GOP1, and the encoding unit 320 performs re-encoding.
- the encoding parameter for re-encoding set from the parameter adjustment unit 370 is used (S313).
- the pre-filter unit 321 applies a pre-filtering process to the encoding target picture with a pre-filter strength corresponding to the encoding parameter for re-encoding (a degree of blurring is greater than the default encoding parameter).
- the DCT coefficient generated in this picture is quantized by the quantization unit 322 with a quantization parameter (a quantization step size is larger than the default encoding parameter) according to the re-encoding encoding parameter.
- the retry point is set to the first picture of GOP1 or the first picture of GOP2 according to the CPB residual code amount at that time, The encoding process for the first picture proceeds.
- the conceptual diagram of the change of the encoding parameter when re-encoding is performed on the intermediate picture of GOP2 is as shown in FIG.
- a re-encoding encoding parameter that suppresses the generated code amount is set, and the head of GOP2 is set.
- the quantization statistic does not exceed the predetermined threshold due to re-encoding, the encoding parameter for re-encoding is returned to the default encoding parameter in the next GOP3 encoding, and the encoding process is continued.
- the conceptual diagram of the transition of the CPB residual code amount when re-encoding is performed is as shown in FIG.
- the portion indicated by the bold line is the CPB remaining code amount after re-encoding.
- the degree of blurring is increased by the pre-filter, and the quantization parameter is made larger than the default encoding parameter. Therefore, the generated code amount is suppressed, and the transition of the remaining CPB code amount is as shown in FIG. 8, for example. .
- the CPB residual code amount in a picture that has undergone re-encoding increases at the time of re-encoding and that the picture quality is greatly deteriorated in the picture.
- the conceptual diagram of the transition of the quantization statistics when re-encoding is performed is as shown in FIG.
- the quantization statistic of the picture that has started re-encoding becomes large.
- the CPB residual code amount is increased as shown in FIG. Since there is a margin, the quantization statistic is smaller in the picture where re-encoding has occurred than before re-encoding.
- FIG. Case 4 The conceptual diagram of the transition of the quantization statistic when re-encoding is performed and it cannot be avoided that the quantization statistic exceeds the threshold even by re-encoding is as shown in FIG. Case 4 may occur when the quantization statistic is already large at the beginning of the GOP at which re-encoding is started, as shown in FIG. 10, for example.
- the quantization statistic calculation unit 340 detects that the quantization statistic exceeds a predetermined threshold, and the operation for re-encoding GOP2 is the same as in case 3. If the quantization statistic exceeds a predetermined threshold during re-encoding of GOP2 (S303, S311), the re-encoding is not performed and the encoding process is continued (transition to S304).
- the quantization parameter becomes larger at the time of re-encoding than at the time of normal encoding, so that at the time of re-encoding, the quantization statistic of the past picture in the encoding order is higher than the picture that triggered the re-encoding. May exceed the threshold. To reduce the possibility that this will occur, if the quantization parameter during re-encoding is larger than the quantization statistic threshold, the re-encoding quantization parameter is modified to a value equal to the quantization statistic threshold. May be.
- the quantization during re-encoding Set the parameter value equal to the normal encoding value.
- FIG. 19 is a process flowchart showing the moving picture coding control method according to the present embodiment.
- NM is called the inter-picture distance for the Mth picture and the Nth picture (N> M) in the coding order.
- the maximum inter-picture distance which is the maximum inter-picture distance that can be traced back within the memory limit at the time of re-encoding, is obtained and stored based on information on the amount of available memory given from the outside (S400).
- the next picture after the picture that has been encoded in the input video signal (the leading picture of the input video signal at the start of encoding) is set as an encoding target (step S401).
- the input picture set as the encoding target is defined as H.264. H.264 or other predetermined encoding method is used (step S402). It is determined whether or not the quantization statistic of the picture when the input picture is encoded exceeds a predetermined threshold (step S403). If the quantization statistic exceeds the predetermined threshold, the processing is performed. The process proceeds to step S407.
- step S404 it is determined whether or not the final picture has been encoded. If the quantization statistic does not exceed the predetermined threshold value, it is determined whether or not the final picture has been encoded (step S404). If the encoding is completed up to the final picture, the encoding process is terminated.
- step S405 it is determined whether or not encoding of the encoding order picture group has been completed. If the encoding order picture group has not been encoded, the process returns to step S401, and the encoding process is continued in the same manner for the next picture.
- the encoding parameter is changed by re-encoding (retry) of the encoding order picture group, the encoding parameter is returned to the value at the time of normal encoding ( In step S406), the process returns to step S401, and the encoding process is performed from the first picture in the next encoding order picture group.
- step S403 If it is detected in step S403 that the quantization statistic exceeds a predetermined threshold value, it is determined whether or not the current coding-order picture group has been re-encoded (retry has been completed) (step S407). ). If the retry has been completed, no further re-encoding is performed, and the process proceeds to step S404 to continue the encoding process.
- a retry point is set to re-encode the pictures in the current encoding order picture group. That is, the farthest picture included in the encoding order picture group being encoded within the range of the maximum inter-picture distance calculated in step S400 is set as an encoding target (step S408). Then, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (the quantization parameter changes the step size more greatly, and in the case of the filter strength, the blurring degree changes more greatly) ( In step S409), the process returns to step S402 to re-encode from the pictures in the encoding order picture group set as the retry point.
- the two encoding parameters quantization parameter, prefilter strength
- the encoding order picture group for example, A plurality of pictures in (GOP) are encoded twice.
- the encoding order picture group for example, A plurality of pictures in (GOP) are encoded twice.
- the encoding order picture group for example, A plurality of pictures in (GOP) are encoded twice.
- the CPB residual code amount further increases.
- FIG. 20 is a process flowchart showing a moving picture coding control method according to a modification of the present embodiment.
- the process of step S406 shown in FIG. 19 can be replaced with the processes of steps S461 to S463 shown in FIG. Processing other than step S406 is the same as that in FIG.
- step S461 it is determined whether or not the encoding parameter has been changed by retry. If the encoding parameter has not been changed by retry, the processing returns to step S401 in FIG. If the coding parameter has been changed by retry, it is next determined whether or not the CPB remaining code amount is equal to or greater than a predetermined threshold (step S462). If the CPB residual code amount is less than the predetermined threshold value, the encoding parameter remains in the state used for re-encoding, and the encoding parameter is restored to the original default encoding only when the CPB residual code amount is equal to or larger than the predetermined threshold value. Return to the parameter (step S463). Thereafter, the process returns to step S401 in FIG. 19 and proceeds to encoding of the next encoding order picture group.
- the encoding parameter is returned to the normal encoding value only when the CPB remaining code amount exceeds a predetermined amount when the encoding of the encoding order picture group is completed. This is due to the following reason. Even if encoding of the encoding order picture group is completed, if the CPB residual code amount is small, the generated encoding amount increases when the encoding parameter is returned to the value at the time of normal encoding. When the picture group is encoded, the possibility that the quantization statistic of the encoded picture exceeds a predetermined threshold again increases. In the process of FIG. 20, when the CPB residual code amount is small, the encoding parameter is not changed. Therefore, compared to the process of FIG. 19, the occurrence of re-encoding in the encoding of the next encoding order picture group is suppressed. As a result, the amount of calculation is further reduced.
- the encoding parameter is changed during re-encoding.
- a pre-filter is applied to the input video during encoding, and the encoding parameters to be changed are a quantization parameter and a pre-filter strength. Both of these two encoding parameters may be changed, or only one of them may be changed.
- Quantization parameters are re-encoded with a larger quantization parameter by adding a predetermined offset value to the quantization parameter value during normal encoding.
- a Gaussian filter is used in this embodiment.
- the Gaussian filter can be created by sampling a Gaussian distribution represented by the following equation with respect to x and y.
- g (x, y) ⁇ 1 / (2 ⁇ 2 ) ⁇ ⁇ exp ⁇ (x 2 + y 2 ) / (2 ⁇ 2 ) ⁇
- the greater the value of ⁇ the greater the degree of blurring.
- the degree of blurring increases, the high frequency components decrease, and the amount of generated code during encoding decreases. Details of the Gaussian filter are described in Non-Patent Document 2 described above, for example.
- the Gaussian filter is not applied.
- the type of the low pass filter is not limited.
- how to increase the degree of blurring during re-encoding may be arbitrarily determined in advance.
- the default encoding parameter ⁇ 0 may be changed in accordance with the complexity of each picture, and ⁇ 1 may be a value obtained by adding a predetermined offset to ⁇ 0 .
- quantization statistics in this embodiment, an average value of quantization parameters of each macroblock of a picture is used.
- Encoding is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP.
- a conceptual diagram of the GOP at the time of encoding is as shown in FIG.
- One GOP is composed of 10 pictures, and B pictures and P pictures are alternately arranged with the I picture at the head in the display order.
- FIG. 21 shows an apparatus configuration example of this embodiment.
- the maximum inter-picture distance determining unit 500 is notified of the usable memory amount from the outside (usable memory amount information), and obtains the maximum inter-picture distance that can be traced back at the maximum when re-encoding based on this.
- the input video signal of the GOP being encoded is stored in the input buffer 410 and the encoded stream of the GOP being encoded is stored in the output buffer 430.
- the maximum inter-picture distance determination unit 500 starts from the case where the GOP length is set to the maximum inter-picture distance, and reduces the maximum inter-picture distance value while reducing the amount of necessary memory in the worst case of the input buffer 410 and the output buffer 430, and the like.
- the inter-picture distance at which the sum of the used memory amounts becomes equal to or less than the usable memory amount is determined, and the maximum inter-picture distance is determined.
- the required memory amount of the input buffer 410 is as follows.
- the required memory amount of input buffer (maximum distance between pictures + 1) x (data amount of one picture)
- the required memory amount of the output buffer 430 is the maximum code amount that can be generated without causing CPB underflow under the restrictions of the size of the CPB and the bit rate. Specifically, when the CPB residual code amount is equal to the CPB size immediately before the start of the GOP code, and all the data input to the CPB according to the bit rate is used up (the CPB residual code amount is 0 after GOP encoding). Is the maximum amount of code that can be generated. As a calculation formula in terms of the number of bits, the required memory capacity of the output buffer is as follows.
- Required memory size of output buffer (bit rate / number of pictures per second) ⁇ (maximum inter-picture distance + 1) + (size of CPB in number of bits)
- H. In the case of H.264, it is necessary to leave the decoded image created during the GOP encoding as a reference image in preparation for re-encoding (if not, it is necessary to encode from the retry point at the time of re-encoding. No reference image). Since pictures in the GOP do not refer to pictures prior to the GOP, the reference picture is stored in the DPB (Decoded Picture Buffer) as long as I and P pictures are presupposed. In all situations, there will be enough memory.
- DPB Decoded Picture Buffer
- FIG. 22 is a conceptual diagram for explaining the required memory amount.
- the GOP has a 10-picture configuration and the maximum inter-picture distance is 6.
- the maximum number of pictures to be held in the input buffer 410 is seven.
- the decoded images of the first I picture and the next P picture also need to be stored in the memory as reference images.
- two DPBs of the first I picture and the second P picture reference numeral RS22 in FIG. 22
- the number of pictures to be held in the input buffer 410 is reduced by three. In other words, the smaller the maximum inter-picture distance, the greater the amount of memory for the reference image. .
- a memory for the motion vector may be necessary.
- the necessary memory is calculated depending on the encoder configuration. The maximum inter-picture distance is determined by obtaining the inter-picture distance whose sum is less than the usable memory amount.
- the maximum inter-picture distance determination unit 500 is not notified of the amount of available memory from the outside and the maximum inter-picture distance is calculated, but the maximum inter-picture distance is calculated externally, and the maximum inter-picture distance is determined. You may make it give to the distance determination part 500 between pictures.
- the maximum inter-picture distance determination unit 500 notifies the retry point management unit 460 of the determined maximum inter-picture distance information.
- the input buffer 410 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 420. Further, when the input buffer 410 receives information (retry information) indicating that re-encoding is performed when the quantization statistic exceeds a predetermined threshold from the quantization statistic calculation unit 440 described later, The video signal is output again from the retry point picture notified from the point management unit 460 to the encoding unit 420. Further, when the retry point information is notified from the retry point management unit 460, the input buffer 410 discards the stored video signal data corresponding to the pictures before the retry point.
- retry information information indicating that re-encoding is performed when the quantization statistic exceeds a predetermined threshold from the quantization statistic calculation unit 440 described later.
- the video signal is output again from the retry point picture notified from the point management unit 460 to the encoding unit 420. Further, when the retry point information is notified from the retry point management unit 460
- the encoding unit 420 encodes the video signal input from the input buffer 410 and outputs the encoded stream to the output buffer 430. Also, the encoding unit 420 outputs the quantization parameter (quantization parameter information) generated when the input video signal is encoded to the quantization statistic calculation unit 440 when the encoding of the picture is completed. At the same time, information indicating that the picture has been encoded (encoding completed picture information) is output to the retry point management unit 460. Further, when receiving the retry information from the quantization statistic calculation unit 440, the encoding unit 420 receives the video signal from the retry point picture in the GOP being encoded again from the input buffer 410 and adjusts the parameters. Since the encoding parameter for re-encoding is input from the unit 450, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 430 stores the encoded stream that is the GOP encoding result and, when notified of the retry point information from the retry point management unit 460, corresponds to the pictures before the retry point that have been stored so far.
- the encoded stream is output and the data is removed from the output buffer 430.
- the encoded stream accumulated for the GOP being encoded is discarded.
- the quantization statistic calculation unit 440 uses the quantization parameter information input from the encoding unit 420 to obtain a quantization statistic that changes in units of pictures. When the quantization statistic exceeds a predetermined threshold, the quantization statistic calculation unit 440 outputs the retry information to the input buffer 410, the encoding unit 420, the parameter adjustment unit 450, and the output buffer 430, and performs quantization. Notify that the statistic exceeds a predetermined threshold.
- the parameter adjustment unit 450 When receiving the retry information from the quantization statistic calculation unit 440, the parameter adjustment unit 450 inputs the encoding parameter for re-encoding to the encoding unit 420 as described above. As a result, the encoding unit 420 encodes the same GOP using an encoding parameter with a small generated code amount at the time of re-encoding.
- the retry point management unit 460 indicates where the retry point becomes when the quantization statistic exceeds a predetermined threshold in the encoding of the next picture based on the encoding complete picture information and the maximum inter-picture distance information.
- the retry point information is notified to the input buffer 410 and the output buffer 430.
- a process for encoding a certain GOP will be described in three cases as follows.
- default encoding parameters are used, and a filtering process by the prefilter unit 421 is applied to a picture to be encoded with a prefilter strength corresponding to the default encoding parameters. Also, the DCT coefficient generated in this picture is quantized by the quantization unit 422 with a quantization parameter according to the default encoding parameter.
- the quantization statistic calculation unit 440 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 420. In this example, since the quantization statistic does not exceed a predetermined threshold, the quantization statistic calculation unit 440 does not output retry information (S403). If the encoding target picture is the final picture in the input video signal, the output buffer 430 outputs the stored encoded stream, and the encoding process is completed (S404). Alternatively, if the current picture to be encoded is the last picture of the GOP, the output buffer 430 outputs the stored encoded stream, the input buffer 410 discards the stored picture, and the processing is performed on the next GOP. The process proceeds to the first picture encoding process (S405). Here, since re-encoding has not occurred in the GOP, the process proceeds to the encoding process of the first picture of the next GOP without changing the encoding parameter (S406).
- the quantization statistic calculation unit 440 calculates a quantization statistic for the picture based on the quantization parameter information input from the encoding unit 420. As a result, when the quantization statistic calculation unit 440 detects that the quantization statistic exceeds a predetermined threshold for the picture, the quantization statistic calculation unit 440 includes the encoding unit 420 and the parameter adjustment unit 450. The retry information is output to the input buffer 410 and the output buffer 430 (S403).
- the input buffer 410 When retry has not yet occurred for the GOP being encoded (S407), the input buffer 410 outputs the picture at the position indicated by the retry point in the GOP being stored to the encoder 420 ( In step S408, the parameter adjustment unit 450 outputs the encoding parameter for re-encoding to the encoding unit 420 (S409). Furthermore, the output buffer 430 discards the encoded stream of the GOP being encoded. Then, the encoding unit 420 encodes the picture after the retry point input using the encoding parameter for re-encoding.
- the encoding parameter for re-encoding is used in encoding, and the pre-filter strength corresponding to the encoding parameter for re-encoding (the blurring degree is greater than the default encoding parameter) is applied to the picture to be encoded.
- a pre-filtering process by the filter unit 421 is applied.
- the DCT coefficient generated in this picture is quantized by the quantization unit 422 with a quantization parameter (a quantization step size is larger than the default encoding parameter) according to the re-encoding encoding parameter.
- the pictures of the GOP are sequentially input from the input buffer 410 to the encoding unit 420, and the encoding unit 420 performs the encoding process.
- the encoding unit 420 sets the encoding parameter to the default encoding parameter ( S406), the process proceeds to the encoding process of the next GOP.
- the operation when the encoding of the last picture of the input video is completed is the same as the case 1 described above.
- the conceptual diagram of changing the encoding parameter when re-encoding is performed is as shown in FIG.
- a re-encoding encoding parameter that suppresses the generated code amount is set, and the maximum Re-encoding is performed from the first I picture of GOP2 within the distance between pictures. Since the quantization statistic does not exceed a predetermined threshold due to re-encoding, in the next GOP3 encoding, the encoding parameter for re-encoding is returned to the default encoding parameter and the encoding process is continued. .
- the conceptual diagram of the transition of the CPB residual code amount when re-encoding is performed is as shown in FIG.
- the portion indicated by the bold line is the CPB remaining code amount after re-encoding.
- the degree of blurring is increased by the pre-filter, and the quantization parameter is made larger than the default encoding parameter. Therefore, the generated code amount is suppressed, and the transition of the remaining CPB code amount is as shown in FIG. 8, for example. .
- the CPB residual code amount in a picture that has undergone re-encoding increases at the time of re-encoding and that the picture quality is greatly deteriorated in the picture.
- the conceptual diagram of the transition of the quantization statistics when re-encoding is performed is as shown in FIG.
- the quantization statistic of the picture that has started re-encoding becomes large.
- the CPB residual code amount is increased as shown in FIG. Since there is a margin, the quantization statistic is smaller in the picture where re-encoding has occurred than before re-encoding.
- FIG. 23 is a diagram for explaining the memory reduction of the input buffer and the output buffer by limiting the retry point with the maximum inter-picture distance.
- a retry point is set according to the present embodiment will be described as “Case A”.
- a picture that starts re-encoding when a quantization statistic exceeds a predetermined threshold may be always set as the first picture of a coding-order picture group (for example, GOP). . This is called “Case B”.
- the currently encoded picture is the ninth B picture of GOP2 and the maximum inter-picture distance is “5” as shown in FIG.
- the retry point becomes the fourth picture (P picture) of GOP2, and the three pictures from the beginning of GOP2 before that are not used for re-encoding. For this reason, the data in the input buffer 410 and the output buffer 430 corresponding to these pictures need not be retained and can be discarded (reference numeral RS23 in FIG. 23).
- these pictures are stored in the input buffer 410 and the output buffer 430 from the start of encoding the first picture of GOP2 until the end of encoding of the last picture of GOP2. Since it is necessary to hold data corresponding to the above, the amount of memory required increases.
- the maximum inter-picture distance is calculated and the retry point is set, so that the amount of memory can be reduced as compared with Case B.
- FIG. Case 3 The conceptual diagram of the transition of the quantization statistic when re-encoding is performed and it cannot be avoided that the quantization statistic exceeds the threshold even by re-encoding is as shown in FIG. Case 3 can occur, for example, as shown in FIG. 10, when the quantization statistics are already large at the head of the GOP at which re-encoding is started.
- the quantization statistic calculation unit 440 detects that the quantization statistic exceeds a predetermined threshold, and the operation for re-encoding the GOP is the same as in case 2. If the quantization statistic exceeds a predetermined threshold during the re-encoding of the GOP (S403, S407), the re-encoding is not performed and the encoding process is continued (the process moves to S404).
- the quantization parameter becomes larger at the time of re-encoding than at the time of normal encoding, so that at the time of re-encoding, the quantization statistic of the past picture in the encoding order rather than the picture that triggered re-encoding May exceed the threshold.
- the quantization statistic threshold is modified to a value equal to the quantization statistic threshold. May be.
- the quantization during re-encoding Set the parameter value equal to the normal encoding value.
- the above-described video encoding control process can be realized by a computer and a software program, and the program can be recorded on a computer-readable recording medium or provided through a network.
- the present invention can be used for, for example, a moving image encoding technique for encoding a video signal. According to the present invention, it is possible to encode a video signal so that a virtual buffer such as an encoded picture buffer in a virtual decoder does not break down and deterioration in image quality does not increase.
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Abstract
Description
本願は,2010年5月12日に日本へ出願された日本特願2010-109874号,日本特願2010-109875号,日本特願2010-109876号,日本特願2010-109877号,日本特願2010-109878号に対して優先権を主張し,それらの内容をここに援用する。
1パス符号化では,入力されるピクチャを逐次的に符号化するため,符号化対象ピクチャより未来のピクチャの性質が分からない。そこで,過去に符号化したピクチャの発生符号量等から未来のピクチャの複雑度を推定し,CPBアンダーフローを抑制する。例えば,特許文献1の技術では,各ピクチャの符号化前に,過去に符号化した結果から得られた映像の複雑度を,GOP(Group Of Pictures)の残りの映像の複雑度の推定値とする。その複雑度の推定値を前提として,CPBの残符号量からGOPの残りの映像の符号化に利用できる最大の符号量を発生させる量子化パラメータを推定し,これを符号化対象ピクチャの符号化の量子化パラメータの下限値として利用することで,CPBアンダーフローを抑制する。このため,単純なシーンから複雑なシーンに移るような場合においては,単純なシーンの符号化時には未来も同等であるとして符号量を発生させ,複雑なシーンでは,CPBに画質を保つために必要な残符号量がなく,大きな量子化パラメータを利用して符号化することになる。結果として,画質が大きく劣化する問題がある。
2パス符号化では,入力映像の全ピクチャを符号化し,その際に発生した各ピクチャの符号量を2回目の符号化で利用する。この方法では,1パス符号化の場合と異なり,2回目の符号化時に映像の各部分の複雑さが分かることから,画質の劣化を抑えつつCPBアンダーフローを抑制できることを期待できる。例えば特許文献2の技術では,1回目の符号化で各フレームの複雑度を求め,各フレームの割り当て符号量を求める。そして,この割り当て符号量でCPBアンダーフローが生じるか否かを検証し,CPBアンダーフローが生じる場合には割り当て符号量を修正する。このように,各フレームの複雑度が分かっているため,CPBアンダーフローを抑制しつつも画質を保つことが期待できる。しかしながら,この方法は入力映像の全フレームを2回符号化するため,多くの演算量を要するという問題がある。
(1)符号化順ピクチャ群の符号化が完了した時点で,CPB残符号量が所定の閾値以上あった場合,リトライポイントを次の符号化順ピクチャ群の先頭ピクチャ(Iピクチャ)に設定する。
(2)符号化順ピクチャ群の符号化が完了した時点で,CPB残符号量が所定の閾値より小さかった場合,リトライポイントはそのままで次の符号化順ピクチャ群の先頭ピクチャの符号化に進む。その符号化順ピクチャ群の先頭ピクチャの符号化で量子化統計量が所定の閾値を超えなかった場合,リトライポイントを現在符号化した符号化順ピクチャ群の先頭ピクチャに設定する。
・条件1:当該ピクチャが,符号化中の符号化順ピクチャ群に含まれること。
・条件2:当該ピクチャが,量子化統計量が所定の閾値を超えたピクチャを基準として,最大ピクチャ間距離に含まれること。
・条件3:条件1,2を満たすピクチャの中で,量子化統計量が所定の閾値を超えたピクチャから最も遠いピクチャであること。
以下,本発明の第1実施形態を,図面を用いて詳細に説明する。図3は,本発明の第1実施形態に係る動画像符号化制御方法を示す処理フローチャートである。
上記の式から分かるように,σの値が大きいほど,ぼかし度合いが大きくなる。ぼかし度合いが大きいほど,高周波数成分が減るため,符号化時の発生符号量が減ることになる。ガウシアンフィルタの詳細は,例えば以下の非特許文献2に記載されている。
〔非特許文献2〕:奥富,小沢,清水,堀,“デジタル画像処理”,財団法人画像情報教育振興協会,2006,pp.108-110.
σ=0の場合には,ガウシアンフィルタをかけないものとし,例えばデフォルト符号化パラメータはσ0 =0,再符号化用符号化パラメータはσ1 >0とする。なお,本実施形態ではローパスフィルタの種類は問わない。また,再符号化時のぼかし度合いの強め方も予め任意に定めてよい。例えば,デフォルト符号化パラメータのσ0 は,ピクチャごとの複雑度に応じて変更し,σ1 はσ0 に所定のオフセットを足したものであるような構成でもよい。
・[ケース1]:GOPの符号化において量子化統計量が所定の閾値を超えることはなかった。
・[ケース2]:GOPの符号化において量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた。
・[ケース3]:GOPの符号化において量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった。
まず,GOPの符号化において量子化統計量が所定の閾値を超えることがなかった場合のケース1について説明する。GOPのピクチャが入力バッファ10に入力されると,入力バッファ10は当該ピクチャを蓄積するとともに,符号化部20に当該ピクチャを符号化対象ピクチャとして入力する(S1)。そして,符号化部20は当該ピクチャを符号化し,出力バッファ30に符号化ストリームを出力するとともに(出力バッファ30は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部40に出力する(S2)。
次に,GOPの符号化において量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた場合のケース2について説明する。GOPのピクチャが入力バッファ10に入力されると,入力バッファ10は当該ピクチャを蓄積するとともに,符号化部20に当該ピクチャを符号化対象ピクチャとして入力する(S1)。そして,符号化部20は当該ピクチャを符号化し,出力バッファ30に符号化ストリームを出力するとともに(出力バッファ30は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部40に出力する(S2)。ここで,符号化においてはデフォルト符号化パラメータが利用される。
最後に,GOPの符号化において量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった場合のケース3について説明する。
以下,本発明の第2実施形態を,図面を用いて詳細に説明する。図11は,本実施形態に係る動画像符号化制御方法を示す処理フローチャートである。
上記の式から分かるように,σの値が大きいほど,ぼかし度合いが大きくなる。ぼかし度合いが大きいほど,高周波数成分が減るため,符号化時の発生符号量が減ることになる。ガウシアンフィルタの詳細は,例えば上述した非特許文献2に記載されている。
σ=0の場合には,ガウシアンフィルタをかけないものとし,例えばデフォルト符号化パラメータはσ0 =0,再符号化用符号化パラメータは,リトライカウントの値をcとすると,σc とする。σc は,cの値が大きいほど大きな値とする。0<σ1 <σ2 <……である。なお,本実施形態ではローパスフィルタの種類は問わない。また,例えばデフォルト符号化パラメータのσ0 は,ピクチャごとの複雑度に応じて変更し,σc はσc-1 に所定のオフセットを足したものであるような構成でもよい。
・[ケース1]:GOPの符号化において量子化統計量が所定の閾値を超えることがなかった。
・[ケース2]:GOPの符号化において複数回量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた。
・[ケース3]:GOPの符号化において複数回量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった。
まず,GOPの符号化において量子化統計量が所定の閾値を超えることがなかった場合のケース1について説明する。GOPのピクチャが入力バッファ110に入力されると,入力バッファ110は当該ピクチャを蓄積するとともに,符号化部120に当該ピクチャを符号化対象ピクチャとして入力する(S101)。そして,符号化部120は当該ピクチャを符号化し,出力バッファ130に符号化ストリームを出力するとともに(出力バッファ130は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部140に出力する(S102)。
次に,GOPの符号化において複数回,量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた場合のケース2について説明する。ここでは,GOPの符号化を開始する時点でのリトライカウントが1であるとし,同じGOPで2回再符号化が行われた場合を説明する。
最後に,同じGOPの符号化において複数回量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった場合のケース3について説明する。
[第3実施形態]
・条件1:リトライカウントが1以上であること。
・条件2:CPB残符号量が所定の閾値以上であること。
リトライカウントが0の場合,またはCPB残符号量が所定の閾値より少ない場合には,リトライカウントは減らさずに,元のままとする。
上記の式から分かるように,σの値が大きいほど,ぼかし度合いが大きくなる。ぼかし度合いが大きいほど,高周波数成分が減るため,符号化時の発生符号量が減ることになる。ガウシアンフィルタの詳細は,例えば上述した非特許文献2に記載されている。
σ=0の場合には,ガウシアンフィルタをかけないものとし,例えばデフォルト符号化パラメータはσ0 =0,再符号化用符号化パラメータは,リトライカウントの値をcとすると,σc とする。σc は,cの値が大きいほど大きな値とする。0<σ1 <σ2 <……である。なお,本実施形態ではローパスフィルタの種類は問わない。また,例えばデフォルト符号化パラメータのσ0 は,ピクチャごとの複雑度に応じて変更し,σc はσc-1 に所定のオフセットを足したものであるような構成でもよい。
・[ケース1]:GOPの符号化において量子化統計量が所定の閾値を超えることがなかった。
・[ケース2]:GOPの符号化において複数回量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた。
・[ケース3]:GOPの符号化において複数回量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった。
まず,GOPの符号化において量子化統計量が所定の閾値を超えることがなかった場合のケース1について説明する。GOPのピクチャが入力バッファ210に入力されると,入力バッファ210は当該ピクチャを蓄積するとともに,符号化部220に当該ピクチャを符号化対象ピクチャとして入力する(S201)。そして,符号化部220は当該ピクチャを符号化し,出力バッファ230に符号化ストリームを出力するとともに(出力バッファ230は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部240に出力する(S202)。
次に,GOPの符号化において複数回,量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた場合のケース2について説明する。ここでは,GOPの符号化を開始する時点でのリトライカウントが1であるとし,同じGOPで2回再符号化が行われた場合を説明する。
最後に,同じGOPの符号化において複数回量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった場合のケース3について説明する。
以下,本発明の第4実施形態を,図面を用いて詳細に説明する。図16は,本実施形態に係る動画像符号化制御方法を示す処理フローチャートである。
上記の式から分かるように,σの値が大きいほど,ぼかし度合いが大きくなる。ぼかし度合いが大きいほど,高周波数成分が減るため,符号化時の発生符号量が減ることになる。ガウシアンフィルタの詳細は,例えば上述した非特許文献2に記載されている。
σ=0の場合には,ガウシアンフィルタをかけないものとし,例えばデフォルト符号化パラメータはσ0 =0,再符号化用符号化パラメータはσ1 >0とする。なお,本実施形態ではローパスフィルタの種類は問わない。また,再符号化時のぼかし度合いの強め方も予め任意に定めてよい。例えば,デフォルト符号化パラメータのσ0 は,ピクチャごとの複雑度に応じて変更し,σ1 はσ0 に所定のオフセットを足したものであるような構成でもよい。
・[ケース1]:GOP1の符号化において,量子化統計量が所定の閾値を超えるという再符号化条件が成立することなくGOP1の符号化が完了し,次のGOP2の先頭ピクチャの符号化においても再符号化条件が成立しなかった。
・[ケース2]:GOP1の符号化が完了し,次のGOP2の先頭ピクチャの符号化において再符号化条件が成立し,再符号化が必要になった。
・[ケース3]:GOP2の中間のピクチャの符号化において再符号化条件が成立し,再符号化が必要になった。
・[ケース4]:GOP2の中間のピクチャの符号化において再符号化条件が成立し,再符号化でも量子化統計量が閾値を超えるのを回避できなかった。
まず,GOP1の符号化において,量子化統計量が所定の閾値を超えることがなかった場合(再符号化条件が成立しなかった場合)のケース1について説明する。GOP1のピクチャが入力バッファ310に入力されると,入力バッファ310は当該ピクチャを蓄積するとともに,符号化部320に当該ピクチャを符号化対象ピクチャとして入力する(S301)。そして,符号化部320は当該ピクチャを符号化し,出力バッファ330に符号化ストリームを出力するとともに(出力バッファ330は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部340に出力する(S302)。
次に,GOP2の先頭ピクチャの符号化において量子化統計量が所定の閾値を超えたが,その後に再符号化で量子化統計量が閾値を超えるのを回避できた場合のケース2について説明する。ケース1と同様に,GOP1の符号化が完了した時点でのリトライポイント変更有無情報が,CPB残符号量が少ないためにリトライポイントを変更しないことを示す場合,リトライポイント管理部360は,入力バッファ310にリトライポイントはGOP1の先頭のIピクチャであることを通知する。
前のケース2では,GOP2の先頭ピクチャの符号化において量子化統計量が所定の閾値を超えたため,再符号化が必要になった例を説明した。一方,GOP2の先頭ピクチャ以外のピクチャで量子化統計量が所定の閾値を超えた場合には,同様に再符号化用符号化パラメータを用いて,GOP2の先頭ピクチャから再符号化が行われることになる。
最後に,GOP2の中間のピクチャの符号化において量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった場合のケース4について説明する。
[第5実施形態]
上記の式から分かるように,σの値が大きいほど,ぼかし度合いが大きくなる。ぼかし度合いが大きいほど,高周波数成分が減るため,符号化時の発生符号量が減ることになる。ガウシアンフィルタの詳細は,例えば上述した非特許文献2に記載されている。
σ=0の場合には,ガウシアンフィルタをかけないものとし,例えばデフォルト符号化パラメータはσ0 =0,再符号化用符号化パラメータはσ1 >0とする。なお,本実施形態ではローパスフィルタの種類は問わない。また,再符号化時のぼかし度合いの強め方も予め任意に定めてよい。例えば,デフォルト符号化パラメータのσ0 は,ピクチャごとの複雑度に応じて変更し,σ1 はσ0 に所定のオフセットを足したものであるような構成でもよい。
一方で,出力バッファ430の必要メモリ量は,CPBの大きさ,およびビットレートの制限下で,CPBアンダーフローを生じさせずに発生し得る最大の符号量とする。具体的には,GOPの符号開始直前においてCPB残符号量がCPBの大きさと等しい状態で,CPBにビットレートに従って入力されるデータを全て使い切った場合(GOP符号化後にCPB残符号量が0)が,発生し得る最大の符号量となる。ビット数での計算式としては,出力バッファの必要メモリ量は,次式のようになる。
さらに,次のようなデータのデータ量も計算する必要がある場合がある。H.264の場合,再符号化に備えてGOPの符号化中に作成された復号画像を,参照画像として残しておく必要がある(残しておかない場合,再符号化時にリトライポイントから符号化する際の参照画像がない状態となる)。GOP内のピクチャは当該GOP以前のピクチャを参照しないため,参照画像としてDPB(Decoded Picture Buffer)に格納するのは,IおよびPピクチャの前提の場合,次のようにメモリを確保しておけば,あらゆる状況においてメモリが足りることになる。
・[ケース1]:GOPの符号化において量子化統計量が所定の閾値を超えることがなかった。
・[ケース2]:GOPの符号化において量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた。
・[ケース3]:GOPの符号化において量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった。
まず,GOPの符号化において量子化統計量が所定の閾値を超えることがなかった場合のケース1について説明する。GOPのピクチャが入力バッファ410に入力されると,入力バッファ410は当該ピクチャを蓄積するとともに,符号化部420に当該ピクチャを符号化対象ピクチャとして入力する(S401)。そして,符号化部420は当該ピクチャを符号化し,出力バッファ430に符号化ストリームを出力するとともに(出力バッファ430は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部440に出力する。また,符号化部420は,リトライポイント管理部460に,符号化完了ピクチャ情報を出力する(S402)。
次に,GOPの符号化において量子化統計量が所定の閾値を超えたが,再符号化で量子化統計量が閾値を超えるのを回避できた場合のケース2について説明する。GOPのピクチャが入力バッファ410に入力されると,入力バッファ410は当該ピクチャを蓄積するとともに,符号化部420に当該ピクチャを符号化対象ピクチャとして入力する(S401)。そして,符号化部420は当該ピクチャを符号化し,出力バッファ430に符号化ストリームを出力するとともに(出力バッファ430は当該符号化ストリームを出力せず,蓄積する),当該ピクチャに関する量子化パラメータ情報を量子化統計量計算部440に出力する(S402)。ここで,符号化においてはデフォルト符号化パラメータが利用される。
最後に,GOPの符号化において量子化統計量が所定の閾値を超え,再符号化でも量子化統計量が閾値を超えるのを回避できなかった場合のケース3について説明する。
20 符号化部
21 プレフィルタ部
22 量子化部
30 出力バッファ
40 量子化統計量計算部
50 パラメータ調整部
110 入力バッファ
120 符号化部
121 プレフィルタ部
122 量子化部
130 出力バッファ
140 量子化統計量計算部
150 リトライカウント管理部
160 パラメータ調整部
210 入力バッファ
220 符号化部
221 プレフィルタ部
222 量子化部
230 出力バッファ
240 量子化統計量計算部
250 リトライカウント管理部
260 CPB状態予測部
270 パラメータ調整部
310 入力バッファ
320 符号化部
321 プレフィルタ部
322 量子化部
330 出力バッファ
340 量子化統計量計算部
350 CPB状態予測部
360 リトライポイント管理部
370 パラメータ調整部
410 入力バッファ
420 符号化部
421 プレフィルタ部
422 量子化部
430 出力バッファ
440 量子化統計量計算部
450 パラメータ調整部
460 リトライポイント管理部
500 最大ピクチャ間距離決定部
Claims (16)
- デコーダにおける仮想バッファが破綻しないように発生符号量を制御して入力映像信号を符号化する動画像符号化制御方法であって,
所定数のピクチャで構成され,符号化順で連続するピクチャの集まりである符号化順ピクチャ群の各ピクチャについて,所定の符号化パラメータに従って順次符号化するステップと,
前記ピクチャの符号化ごとに,当該ピクチャの符号化において利用した量子化パラメータ情報をもとに当該ピクチャの量子化統計量を算出し,前記量子化統計量が所定の閾値を超えたか否かを検査するステップと,
前記量子化統計量が前記所定の閾値を超えた場合に,前記符号化パラメータを符号化による発生符号量が減少するように変更し,符号化中の符号化順ピクチャ群の先頭のピクチャから変更後の符号化パラメータを用いて再符号化するステップと
を有する動画像符号化制御方法。 - 請求項1記載の動画像符号化制御方法において,
前記順次符号化するステップでは,前記符号化順ピクチャ群の各ピクチャを,再符号化回数を示すリトライカウントに応じて設定された符号化パラメータに従って順次符号化し,
前記再符号化するステップでは,前記量子化統計量が前記所定の閾値を超えた場合に,前記リトライカウントを増加させ,前記符号化パラメータを前記リトライカウントの値が大きいほど符号化による発生符号量が減少する符号化パラメータに変更する
動画像符号化制御方法。 - 請求項2記載の動画像符号化制御方法において,
前記符号化順ピクチャ群における最終ピクチャの符号化が完了するまで,符号化した各ピクチャの量子化統計量が前記所定の閾値を超えなかった場合に,前記仮想バッファの残符号量を調べ,前記残符号量が所定の残符号量閾値未満または前記リトライカウントが0であれば,前記リトライカウントの値を変更せず,前記残符号量が前記残符号量閾値以上かつ前記リトライカウントが0でなければ,前記リトライカウントを減少させるステップを有する
動画像符号化制御方法。 - 請求項2記載の動画像符号化制御方法において,
前記符号化順ピクチャ群における最終ピクチャの符号化が完了するまで,符号化した各ピクチャの量子化統計量が前記所定の閾値を超えなかった場合に,前記リトライカウントを減少させるステップを有する
動画像符号化制御方法。 - 請求項2から請求項4までのいずれか1項に記載の動画像符号化制御方法において,
前記符号化パラメータは,量子化パラメータもしくは前記入力映像信号に対するプレフィルタのフィルタ強度,またはその双方であり,前記符号化パラメータが前記量子化パラメータの場合には,前記リトライカウントの値が大きいほど,前記量子化パラメータのステップサイズが大きい符号化パラメータが設定され,前記符号化パラメータが前記プレフィルタの前記フィルタ強度の場合には,前記リトライカウントの値が大きいほど,フィルタリング処理によるぼかし度合いが大きい符号化パラメータが設定される
動画像符号化制御方法。 - デコーダにおける仮想バッファが破綻しないように発生符号量を制御して入力映像信号を符号化する動画像符号化制御方法であって,
画面内予測符号化ピクチャを先頭とする所定数のピクチャで構成され,符号化順で連続するピクチャの集まりである符号化順ピクチャ群の各ピクチャについて,所定の符号化パラメータに従って順次符号化するステップと,
前記ピクチャの符号化ごとに,当該ピクチャの符号化において利用した量子化パラメータ情報をもとに当該ピクチャの量子化統計量を算出し,前記量子化統計量が所定の閾値を超えたか否かを検査するステップと,
前記量子化統計量が前記所定の閾値を超えた場合に,前記符号化パラメータを符号化による発生符号量が減少するように変更し,リトライポイントとして設定された符号化順ピクチャ群の先頭のピクチャから変更後の符号化パラメータを用いて再符号化するステップと,
前記符号化順ピクチャ群の符号化が完了したときに,前記仮想バッファの残符号量を調べ,前記残符号量が所定の残符号量閾値以上であれば,前記リトライポイントを次の符号化順ピクチャ群の先頭ピクチャに設定し,前記仮想バッファの前記残符号量が前記所定の残符号量閾値未満であれば,前記リトライポイントを変更せず,前記次の符号化順ピクチャ群の前記先頭ピクチャの符号化において前記量子化統計量が前記所定の閾値を超えなかったときに,前記リトライポイントを当該符号化順ピクチャ群の先頭ピクチャに設定するステップとを有する
動画像符号化制御方法。 - デコーダにおける仮想バッファが破綻しないように発生符号量を制御して入力映像信号を符号化する動画像符号化制御方法であって,
所定数のピクチャで構成され,符号化順で連続するピクチャの集まりである符号化順ピクチャ群の各ピクチャについて,所定の符号化パラメータに従って順次符号化するステップと,
前記ピクチャの符号化ごとに,当該ピクチャの符号化において利用した量子化パラメータ情報をもとに当該ピクチャの量子化統計量を算出し,前記量子化統計量が所定の閾値を超えたか否かを検査するステップと,
前記量子化統計量が前記所定の閾値を超えた場合に,前記符号化パラメータを符号化による発生符号量が減少するように変更し,符号化中の符号化順ピクチャ群においてリトライポイントとして設定されたピクチャから変更後の符号化パラメータを用いて再符号化するステップと,
再符号化時に,再符号化対象のピクチャとして遡ることができる最大のピクチャ数である最大ピクチャ間距離をもとに,前記再符号化を開始するピクチャの位置を示すリトライポイントを設定するステップとを有する
動画像符号化制御方法。 - 請求項1,請求項6または請求項7記載の動画像符号化制御方法において,
前記符号化順ピクチャ群の再符号化において当該符号化順ピクチャ群の最終のピクチャの符号化が完了するまで,符号化した各ピクチャの量子化統計量が前記所定の閾値を超えなかった場合に,次の符号化順ピクチャ群の符号化に用いる符号化パラメータを,通常の符号化時の符号化パラメータ値に戻す
動画像符号化制御方法。 - 請求項1,請求項6または請求項7記載の動画像符号化制御方法において,
前記符号化順ピクチャ群の再符号化において,当該符号化順ピクチャ群の最終のピクチャの符号化が完了するまで,前記量子化統計量が前記所定の閾値を超えなかった場合に,前記仮想バッファの残符号量を調べ,前記残符号量が所定の残符号量閾値未満であれば,次の符号化順ピクチャ群の符号化に用いる符号化パラメータを変更せず,前記残符号量が前記所定の残符号量閾値以上であれば,前記符号化パラメータを通常の符号化時の符号化パラメータ値に戻す
動画像符号化制御方法。 - 請求項1,および,請求項6から請求項9までのいずれか1項に記載の動画像符号化制御方法において,
前記符号化パラメータは,量子化パラメータもしくは前記入力映像信号に対するプレフィルタのフィルタ強度,またはその双方であり,前記符号化順ピクチャ群の再符号化時において,前記符号化パラメータが前記量子化パラメータの場合には,再符号化時に前記量子化パラメータのステップサイズを大きくし,前記符号化パラメータが前記プレフィルタの前記フィルタ強度の場合には,フィルタリング処理によるぼかし度合いを大きくする符号化パラメータの変更を行う
動画像符号化制御方法。 - デコーダにおける仮想バッファが破綻しないように発生符号量を制御して入力映像信号を符号化する動画像符号化装置であって,
所定数のピクチャで構成され,符号化順で連続するピクチャの集まりである符号化順ピクチャ群の各ピクチャについて,所定の符号化パラメータに従って順次符号化する符号化部と,
前記ピクチャの符号化ごとに,当該ピクチャの符号化において利用した量子化パラメータ情報をもとに当該ピクチャの量子化統計量を算出し,前記量子化統計量が所定の閾値を超えたか否かを検査し,前記量子化統計量が前記所定の閾値を超えたことを検出した場合にリトライ情報を出力する量子化統計量計算部と,
前記リトライ情報が出力された場合に,前記符号化パラメータを符号化による発生符号量が減少するように変更し,変更された符号化パラメータを前記符号化部へ通知するパラメータ調整部とを備え,
前記符号化部は,前記リトライ情報が出力された場合に,符号化中の符号化順ピクチャ群の先頭のピクチャから,前記パラメータ調整部が変更した符号化パラメータを用いて前記入力映像信号を再符号化する
動画像符号化装置。 - 請求項11記載の動画像符号化装置において,
前記符号化部は,前記符号化順ピクチャ群の各ピクチャを,再符号化回数を示すリトライカウントに応じて設定された符号化パラメータに従って順次符号化し,
前記動画像符号化装置は,前記リトライ情報が出力された場合に,前記リトライカウントを増加させ,前記符号化順ピクチャ群における最終ピクチャの符号化が完了するまで,前記リトライ情報が出力されなかった場合に,前記リトライカウントを減少させるリトライカウント管理部を備え,
前記パラメータ調整部は,前記リトライカウントに応じて定められた,前記リトライカウントの値が大きいほど符号化による発生符号量が減少する符号化パラメータを設定し,設定された符号化パラメータを前記符号化部へ通知する
動画像符号化装置。 - 請求項12記載の動画像符号化装置において,
前記符号化順ピクチャ群における最終ピクチャまで,前記量子化統計量が前記所定の閾値を超えないで符号化が完了した場合に,前記仮想バッファの残符号量が所定の残符号量閾値以上か否かによりパラメータ変更要またはパラメータ変更不要を示すパラメータ変更有無情報を出力するバッファ状態予測部を備え,
前記リトライカウント管理部は,前記バッファ状態予測部から前記パラメータ変更有無情報を入力した場合に,前記パラメータ変更有無情報がパラメータ変更不要を示すかまたは前記リトライカウントが0であれば,前記リトライカウントの値を変更せず,前記パラメータ変更有無情報がパラメータ変更要を示しかつ前記リトライカウントが0でなければ,前記リトライカウントを減少させる
動画像符号化装置。 - デコーダにおける仮想バッファが破綻しないように発生符号量を制御して入力映像信号を符号化する動画像符号化装置であって,
所定数のピクチャで構成され,符号化順で連続するピクチャの集まりである符号化順ピクチャ群の各ピクチャについて,所定の符号化パラメータに従って順次符号化する符号化部と,
前記ピクチャの符号化ごとに,当該ピクチャの符号化において利用した量子化パラメータ情報をもとに当該ピクチャの量子化統計量を算出し,前記量子化統計量が所定の閾値を超えたか否かを検査し,前記量子化統計量が前記所定の閾値を超えたことを検出した場合にリトライ情報を出力する量子化統計量計算部と,
前記リトライ情報が出力された場合に,前記符号化パラメータを符号化による発生符号量が減少するように変更し,変更された符号化パラメータを前記符号化部へ通知するパラメータ調整部と,
前記符号化順ピクチャ群の符号化が完了したときに,前記仮想バッファの残符号量を調べ,前記残符号量が所定の残符号量閾値以上であるか否かを判定するバッファ状態予測部と,
前記バッファ状態予測部の判定結果に従って,前記仮想バッファの前記残符号量が前記所定の残符号量閾値以上であれば,リトライポイントを次の符号化順ピクチャ群の先頭ピクチャに設定し,前記仮想バッファの前記残符号量が前記所定の残符号量閾値未満であれば,前記リトライポイントを変更せず,次の符号化順ピクチャ群の先頭ピクチャの符号化において前記量子化統計量が前記所定の閾値を超えなかったときに,前記リトライポイントを当該符号化順ピクチャ群の先頭ピクチャに設定するリトライポイント管理部とを備え,
前記符号化部は,前記リトライ情報が出力された場合に,前記リトライポイントとして設定された符号化順ピクチャ群の先頭のピクチャから,前記パラメータ調整部が変更した符号化パラメータを用いて前記入力映像信号を再符号化する
動画像符号化装置。 - デコーダにおける仮想バッファが破綻しないように発生符号量を制御して入力映像信号を符号化する動画像符号化装置であって,
所定数のピクチャで構成され,符号化順で連続するピクチャの集まりである符号化順ピクチャ群の各ピクチャについて,所定の符号化パラメータに従って順次符号化する符号化部と,
前記ピクチャの符号化ごとに,当該ピクチャの符号化において利用した量子化パラメータ情報をもとに当該ピクチャの量子化統計量を算出し,前記量子化統計量が所定の閾値を超えたか否かを検査し,前記量子化統計量が前記所定の閾値を超えたことを検出した場合にリトライ情報を出力する量子化統計量計算部と,
前記リトライ情報が出力された場合に,前記符号化パラメータを符号化による発生符号量が減少するように変更し,変更された符号化パラメータを前記符号化部へ通知するパラメータ調整部と,
再符号化時に,再符号化対象のピクチャとして遡ることができる最大のピクチャ数である最大ピクチャ間距離をもとに,前記再符号化を開始するピクチャの位置を示すリトライポイントを設定するリトライポイント管理部とを備え,
前記符号化部は,前記リトライ情報が出力された場合に,符号化中の符号化順ピクチャ群において前記リトライポイントとして設定されたピクチャから,前記パラメータ調整部が変更した符号化パラメータを用いて前記入力映像信号を再符号化する
動画像符号化装置。 - 請求項1から請求項10までのいずれか1項に記載の動画像符号化制御方法を,コンピュータに実行させるための動画像符号化プログラム。
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US9179149B2 (en) | 2015-11-03 |
RU2012147239A (ru) | 2014-06-20 |
CA2798354A1 (en) | 2011-11-17 |
ES2773329T3 (es) | 2020-07-10 |
TW201215150A (en) | 2012-04-01 |
EP2571268A1 (en) | 2013-03-20 |
US20130051458A1 (en) | 2013-02-28 |
EP2571268B1 (en) | 2019-11-27 |
EP2571268A4 (en) | 2015-12-16 |
RU2527740C2 (ru) | 2014-09-10 |
KR101391661B1 (ko) | 2014-05-07 |
BR112012028576A2 (pt) | 2016-08-02 |
JPWO2011142291A1 (ja) | 2013-07-22 |
CA2798354C (en) | 2016-01-26 |
CN102870415A (zh) | 2013-01-09 |
TWI507016B (zh) | 2015-11-01 |
JP5286581B2 (ja) | 2013-09-11 |
KR20130006684A (ko) | 2013-01-17 |
CN102870415B (zh) | 2015-08-26 |
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