WO2011138923A1 - 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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- H04N19/103—Selection of coding mode or of prediction mode
- H04N19/114—Adapting the group of pictures [GOP] structure, e.g. number of B-frames between two anchor frames
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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
- 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 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 the bit rate as indicated by an arrow A1.
- 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.
- the CPB underflow is a situation in which the coded stream of the picture is insufficient in the CPB when the virtual decoder tries to extract the coded stream of the picture at each time indicated by the arrow A2.
- the CPB of the virtual decoder is H.264.
- the following non-patent document 1 describes further details.
- CPB Video Buffering Verifier
- 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”.
- ⁇ Conventional technology b> In the two-pass encoding, all pictures of the input video are encoded, and the code amount of each picture generated at that time is used in the second encoding.
- the complexity of each part of the video is known at the time of the second encoding, so that it can be expected that CPB underflow can be suppressed while suppressing deterioration in image quality.
- the complexity of each frame is obtained by the first encoding, and the allocated code amount of each frame is obtained. Then, whether or not CPB underflow occurs with this allocated code amount is verified. If CPB underflow occurs, the allocated code amount is corrected.
- the allocated code amount can be corrected only when CPB underflow occurs.
- the CPB underflow is suppressed while suppressing the image quality degradation as compared with the prior art a. Can be suppressed.
- this method has a problem that the amount of calculation increases because it is necessary to encode all frames of the input video twice.
- An object of the present invention is to solve the above-described problems and to realize stable image quality while suppressing CPB underflow with a smaller amount of calculation than conventional two-pass coding (conventional technology b).
- the coding order picture group is a collection of pictures that are composed of a predetermined number of pictures starting from the intra prediction coding picture (I picture) and are consecutive in the coding order.
- a typical coding order picture group is GOP (Group Of Pictures).
- FIGS. 2A to 2D Schematic diagrams of the coding order picture group are shown in FIGS. 2A to 2D.
- 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...
- 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.
- FIG. 2D shows an example in which the coding order picture group has a 20-picture configuration corresponding to 2 GOPs.
- 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 encoding of the input video proceeds in units of encoding order pictures.
- CPB is checked for failure by a predetermined buffer test algorithm. Only when CPB underflow occurs, the encoding parameter is changed so that the generated code amount is reduced. Then, the encoding order picture group being encoded is re-encoded.
- 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 be larger.
- 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 changed from the first picture in the encoding order picture group currently being encoded, and re-encoding is performed. That is, as long as CPB underflow occurs, 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.
- a video to be encoded has a complex part and a simple part. If the encoding order picture group to be re-encoded due to CPB underflow is complex or simple, if re-encoding is performed only once, CPB under-flow is performed by re-encoding once. Since it is necessary to suppress the flow, it is necessary to set an encoding parameter for re-encoding with a larger change amount of the encoding parameter. Then, when re-encoding occurs in a complicated portion of the video that can avoid CPB underflow even if the amount of change in the encoding parameter is small, image quality deterioration is larger than necessary.
- the complicated amount of video (when many high-frequency components are included or when the correlation in the time direction is small) has a large amount of information, so the amount of code can be reduced by changing the coding parameters a little. In other words, if the amount of change in the encoding parameter is too large, the image quality is wasted.
- 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,
- image quality deterioration can be further reduced by suppressing the change amount of the encoding parameter to be small and encoding with an appropriate encoding parameter.
- the retry count value when encoding of a coding order picture group is completed, the retry count value is not unconditionally reduced, but when encoding of the coding order picture group is completed.
- the retry count is reduced only when the CPB remaining code amount is equal to or greater than a predetermined threshold.
- 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.
- a video to be encoded has a complex part and a simple part. If the encoding order picture group to be re-encoded due to CPB underflow is complex or simple, if re-encoding is performed only once, CPB under-flow is performed by re-encoding once. Since it is necessary to suppress the flow, it is necessary to set an encoding parameter for re-encoding with a larger change amount of the encoding parameter. Then, when re-encoding occurs in a complicated portion of the video that can avoid CPB underflow even if the amount of change in the encoding parameter is small, image quality deterioration is larger than necessary.
- the complicated amount of video (when many high-frequency components are included or when the correlation in the time direction is small) has a large amount of information, so the amount of code can be reduced by changing the coding parameters a little. In other words, if the amount of change in the encoding parameter is too large, the image quality is wasted.
- 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, By suppressing the change amount of the encoding parameter to be small and encoding with an appropriate encoding parameter, it is possible to further reduce image quality degradation.
- 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).
- the encoding of the input video proceeds in units of encoding order pictures.
- a predetermined buffer test algorithm is used to check whether CPB fails. If CPB underflow occurs, the encoding parameter is changed so that the generated code amount is reduced.
- 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 be larger.
- 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 retry point described above is position information indicating from which picture re-encoding is started when it is necessary to re-encode due to the occurrence of CPB underflow 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. . When CPB underflow does not occur 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 reason for setting retry points as described above will be explained. If the retry point is always set at the head 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”. Also in the related art, only when the CPB underflow occurs, the CPB underflow can be suppressed by re-encoding only the coding order picture group in which it occurred, and all of the input video can be suppressed. The amount of calculation is smaller than that in the conventional technique b in which a picture is encoded twice, and effective code amount distribution control can be realized.
- An object of the present invention is to realize code amount distribution control that reduces the degradation of the image quality of a decoded image by suppressing CPB underflow more effectively than the related art.
- an I picture has a larger amount of generated code than other picture types. Therefore, if the amount of remaining CPB code at the time when encoding of a certain coding order picture group is small, there is a high possibility that CPB underflow will occur in the first I picture of the next coding order picture group. In such a case, in the related art, since it is necessary to avoid CPB underflow by re-encoding only the first I picture in which CPB underflow has occurred, the image quality of the I picture may be greatly degraded. There is.
- the frame of the input video is not always encoded twice as in the conventional two-pass encoding. Basically, only when a CPB underflow occurs, only a plurality of pictures are re-encoded.
- re-encoding is performed retroactively to a certain picture in the encoding order picture group.
- 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 processing outline of the present embodiment 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 input buffer and the output buffer each have a memory capacity corresponding to the number of pictures in the coding order picture group, so that when CPB underflow occurs. Re-encoding can be performed from the beginning of the encoding order picture group in units of the encoding order picture group.
- 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.
- CPB is checked for failure by a predetermined buffer test algorithm. Only when CPB underflow occurs, the encoding parameter is changed so that the generated code amount is reduced. Then, the encoding order picture group being encoded is re-encoded. 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 Included in a coding order picture group being coded.
- Condition 2 Included in the maximum inter-picture distance with reference to a picture in which CPB underflow has occurred.
- Condition 3 A picture farthest from a picture in which CPB underflow has occurred 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 first embodiment of the present invention differs from the conventional two-pass coding (conventional technology b) in which all the frames of the input video are coded twice, and the coding order picture group is changed only when CPB underflow occurs. Encode twice. At the time of re-encoding, encoding is performed with an encoding parameter that suppresses CPB underflow. For this reason, it is possible to reduce the amount of calculation compared to the conventional technique b while suppressing the CPB underflow only when necessary as in the conventional technique b.
- the second and third embodiments of the present invention differ from the conventional two-pass coding (conventional technology b) in which all frames of the input video are coded twice, and only in the case where the CPB underflow occurs.
- a picture group is encoded multiple times. Similar to the first embodiment, encoding is performed with encoding parameters that suppress CPB underflow during re-encoding. For this reason, it is possible to reduce the amount of calculation compared to the conventional technique b while suppressing the CPB underflow only when necessary as in the conventional technique b.
- the amount of change in the encoding parameter at the time of re-encoding can be suppressed and CPB underflow can be suppressed. Degradation of image quality due to encoding can be reduced.
- the encoding parameter is kept the same as that at the time of re-encoding, so that re-encoding occurs. Can be suppressed.
- the fourth embodiment of the present invention differs from the conventional two-pass coding (conventional technology b) in which all the frames of the input video are coded twice, and only when the CPB underflow occurs, the coding order picture group is changed. Encode twice. At the time of re-encoding, encoding is performed with an encoding parameter that suppresses CPB underflow. For this reason, it is possible to reduce the amount of calculation compared to the conventional technique b while suppressing the CPB underflow only when necessary as in the conventional technique b.
- the fourth embodiment of the present invention it is possible to effectively suppress the occurrence of CPB underflow in the leading I picture that has a large amount of generated codes in the coding order picture group. It can be prevented from greatly deteriorating.
- encoding is performed with an encoding parameter that suppresses CPB underflow. For this reason, it is possible to reduce the amount of calculation compared to the conventional technique b while suppressing the CPB underflow only when necessary as in the conventional technique b.
- 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 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 CPB underflow has occurred due to the encoding of the input picture (step S103). If CPB underflow has occurred, the process proceeds to step S107. Whether CPB underflow has occurred is described in, for example, H.B. It can be determined by a method used in the H.264 standard.
- step S104 it is determined whether or not the encoding of the final picture has been completed. If the encoding has been 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 not completed, the process returns to step S101 to continue the encoding process 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 ( Returning to step S106) and step S101, encoding processing is performed from the first picture of the next encoding order picture group.
- step S107 it is determined whether or not the current coding-order picture group has been re-encoded. If the retry has been completed, CPB underflow cannot be avoided even if the encoding-order picture group is re-encoded, and therefore encoding is terminated. If the retry has not been completed, 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 S108).
- step S109 the encoding order picture group being encoded is re-encoded.
- the encoding order picture group (for example, GOP) is encoded twice only when CPB underflow occurs.
- the second encoding encoding is performed with an encoding parameter that suppresses CPB underflow. Only when the CPB underflow occurs, the CPB underflow is suppressed by re-encoding only the coding order picture group in which the CPB underflow has occurred. 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. 4 is a process flowchart showing a modification of the moving picture coding control method according to the first embodiment of the present invention.
- the process in step S106 shown in FIG. 3 can be replaced with the processes in steps S161 to S163 shown in FIG. Processing other than step S106 is the same as that in FIG.
- step S161 it is determined whether or not the encoding parameter has been changed by retry. If it has not been changed by retry, the process returns to step S101 in FIG. If it has been changed by retry, it is next determined whether or not the CPB remaining code amount is equal to or larger than a predetermined threshold (step S162). If it is less than the predetermined threshold value, the encoding parameter remains in the state used in re-encoding, and the encoding parameter is returned to the original default encoding parameter only when it is equal to or greater than the predetermined threshold value (step S163). After that, the process returns to step S101 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. The possibility of CPB underflow increases in the coding of pictures. 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.
- the Gaussian filter can be created by sampling the Gaussian distribution expressed by the following equation (1) with respect to x and y.
- the type of 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 .
- Encoding is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP, and a conceptual diagram of the GOP when 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 apparatus configuration according to the first embodiment of the present invention.
- the input buffer 110 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 120. Furthermore, when receiving information (retry information) indicating that CPB underflow occurs and re-encoding is performed from the CPB management unit 140 (to be described later), the input buffer 110 receives video from the first picture of the GOP being encoded. The signal is output again to the encoding unit 120. 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 CPB underflow occurs and re-encoding is performed from the CPB management unit 140 (to be 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 code amount (code amount information) generated when the input video signal is encoded is output to the CPB management unit 140. Furthermore, when receiving the retry information from the CPB management 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 re-encodes it from the parameter adjustment unit 150. Since the encoding parameter for encoding is input, 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 CPB management unit 140, the output buffer 130 accumulates the GOP being encoded. Discard the encoded stream.
- the CPB management unit 140 uses the code amount information input from the encoding unit 120 to obtain the remaining code amount of the CPB that changes with time. That is, the remaining code amount of CPB shown in the conceptual diagram of FIG. 1 is obtained.
- retry information is output to the input buffer 110, encoding unit 120, parameter adjustment unit 150, and output buffer 130 to notify that CPB underflow has occurred.
- the parameter adjustment unit 150 When the parameter adjustment unit 150 receives the retry information from the CPB management unit 140, the parameter adjustment unit 150 inputs the encoding parameter for re-encoding to the encoding unit 120 as described above. As a result, the encoding unit 120 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.
- default encoding parameters are used, and filtering processing by the prefilter unit 121 is applied to a picture to be encoded with a prefilter strength corresponding to the default encoding parameters, and DCT coefficients generated in the main picture are generated.
- the CPB management unit 140 calculates the remaining CPB code amount for the picture based on the code amount information input from the encoding unit 120. In this example, no CPB underflow occurs, so no retry information is output. (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). 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 (S106).
- the CPB management unit 140 calculates the CPB residual code amount for the picture based on the code amount information input from the encoding unit 120. As a result, when the CPB management unit 140 detects a CPB underflow for the picture, the CPB management unit 140 outputs retry information to the encoding unit 120, the parameter adjustment unit 150, the input buffer 110, and the output buffer 130 ( S103).
- the input buffer 110 When no retry has occurred for the GOP being encoded (S107), the input buffer 110 outputs the accumulated first picture of the GOP being encoded to the encoding unit 120 (S108), and parameter adjustment The unit 150 outputs the encoding parameter for re-encoding to the encoding unit 120 (S109). Further, the output buffer 130 discards the encoded stream of the GOP being encoded. Then, the encoding unit 120 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.
- the pre-filtering process by the filter unit 121 is applied, and the DCT coefficient generated in this picture is quantized by a quantization parameter (a quantization step size is larger than the default coding parameter) according to the encoding parameter for re-encoding. Quantized by the unit 122.
- the pictures of the GOP are sequentially input from the input buffer 110 to the encoding unit 120, and the encoding unit 120 performs the encoding process.
- the encoded stream of the GOP is output from the output buffer 130, and the encoding unit 120 sets the encoding parameter as a default encoding parameter ( S106), 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 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 the first I picture of GOP2 Is re-encoded. Since the occurrence of CPB underflow is suppressed by the re-encoding, in the next GOP3 encoding, the re-encoding encoding parameter is returned to the default encoding parameter, and the encoding process is continued.
- FIG. 8 shows a conceptual diagram of the transition of the remaining CPB code amount when re-encoding is performed.
- the line indicated by the bold line is the CPB remaining code amount after re-encoding.
- the pre-filter increases the degree of blurring and the quantization parameter is larger than the default encoding parameter, so that the amount of generated code is suppressed, for example, the transition shown in FIG. 8 is performed, and CPB underflow is suppressed. Is done.
- FIG. 9 is a process flowchart showing a moving picture coding control method according to the second 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 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 CPB underflow has occurred due to the encoding of the input picture (step S203). If CPB underflow has occurred, the process proceeds to step S208. Whether CPB underflow has occurred is described in, for example, H.B. It can be determined by a method used in the H.264 standard.
- step S204 it is determined whether or not the encoding of the final picture has been completed. If the encoding has been 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 not completed, the process returns to step S201 to continue the encoding process for the next picture.
- the retry count is 1 or more, it is decreased by 1 (step S206). Note that the initial value of the retry count is zero.
- an encoding parameter predetermined according to the retry count is set (step S207), and the process returns to step S201 to perform encoding processing from the first picture in the next encoding order picture group. .
- step S208 When it is detected in step S203 that a CPB underflow has occurred, it is determined whether or not the current retry count value is a predetermined maximum value (step S208). In this case, since the CPB underflow cannot be avoided even if the encoding-order picture group is re-encoded, the encoding is terminated.
- 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). After that, based on the retry count, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (quantization parameter has a larger step size, and in the case of filter strength, the blurring degree is larger. (Change) (step S211), the process returns to step S202, and the encoding order picture group being encoded is re-encoded.
- the present invention is basically a one-time encoding process, and only when a CPB underflow occurs (for example, an encoding order picture group (for example, GOP) is repeatedly encoded with the generated code amount being reduced in steps until no CPB underflow occurs.
- a CPB underflow for example, an encoding order picture group (for example, GOP)
- encoding is performed with an encoding parameter that suppresses CPB underflow 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 as in the first embodiment.
- the Gaussian filter can be created by sampling the Gaussian distribution expressed by the above-described equation (1) with respect to x and y.
- the type of 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 .
- the encoding method is H.264. It is assumed that encoding according to the H.264 standard is performed. Further, the encoding order picture group is GOP, and FIG. 5 shows a conceptual diagram of GOP when encoding. As in the first embodiment, 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. 10 shows an apparatus configuration example of the second embodiment of the present invention.
- the input buffer 210 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 220. Further, when receiving input information (retry information) indicating that CPB underflow occurs and re-encoding is performed from the CPB management unit 240 (to be described later), the input buffer 210 receives video from the first picture of the GOP being encoded. The signal is output again to the encoding unit 220. When the GOP encoding is completed without receiving retry information, the input buffer 210 discards the stored video signal of the GOP.
- retry information input information indicating that CPB underflow occurs and re-encoding is performed from the CPB management unit 240 (to be 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 code amount (code amount information) generated when the input video signal is encoded is output to the CPB management unit 240. Further, when receiving the retry information from the CPB management unit 240, the encoding unit 220 receives the video signal from the leading picture of the GOP being encoded again from the input buffer 210 and re-encodes it from the parameter adjustment unit 260. Since the encoding parameter for encoding is input, 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 CPB management unit 240, the output buffer 230 stores the GOP being encoded. Discard the encoded stream.
- the CPB management unit 240 uses the code amount information input from the encoding unit 220 to obtain the remaining code amount of the CPB that changes with time. That is, the remaining code amount of CPB shown in the conceptual diagram of FIG. 1 is obtained.
- retry information is output to the input buffer 210, the encoding unit 220, the retry count management unit 250, and the output buffer 230 to notify that CPB underflow has occurred.
- the parameter adjustment unit 260 When the parameter adjustment unit 260 receives the retry count from the retry count management unit 250, the parameter adjustment unit 260 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.
- this embodiment introduces the concept of retry count that increases when re-encoding occurs and decreases when GOP encoding is completed, and is managed by the retry count management unit 250.
- 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.
- the filtering process is applied, and the DCT coefficient generated in this picture is quantized by the quantization unit 222 with the 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 CPB management unit 240 calculates the remaining CPB code amount for the picture based on the code amount information input from the encoding unit 220. In this example, no CPB underflow occurs, so no retry information is output. (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 retry count management unit 250 decrements the value from the current retry count by 1 except when the retry count is 0 (S206). ).
- 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 250 notifies the parameter adjustment unit 260 of the retry count after the change, and the parameter adjustment unit 260 sets the encoding parameter corresponding to the notified retry count in the encoding unit 220 and the next GOP. Encoding of the first picture is started.
- 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 but stores it), and sends it to the CPB management unit 240 related to the picture.
- the code amount information is output (S202).
- an encoding parameter corresponding to retry count 1 is used.
- the CPB management unit 240 calculates the remaining CPB code amount for the picture based on the code amount information input from the encoding unit 220. As a result, when the CPB management unit 240 detects a CPB underflow for the picture, the CPB management unit 240 outputs retry information to the encoding unit 220, the retry count management unit 250, 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 260 (S210).
- the parameter adjustment unit 260 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 a CPB underflow occurs, GOP pictures are sequentially input from the input buffer 210 and encoded.
- the retry count is incremented by 1 and becomes 3 by the same processing as described above.
- the retry count management unit 250 decrements the retry count by 1, sets the retry count to 2, and proceeds with the encoding of the next GOP.
- the operations of the input buffer 210 and the output buffer 230 at this time are the same as in the above-described example.
- Fig. 11 shows a conceptual diagram of retry count and coding parameter transition in the case 2 example.
- the retry count is set to 2 and the retry is performed again.
- FIG. 8 shows a conceptual diagram of the transition of the remaining CPB code amount when re-encoding is performed. Similar to the first embodiment, the bold line indicates the CPB residual code amount after re-encoding.
- the pre-filter increases the degree of blurring and the quantization parameter is larger than the default encoding parameter, so that the amount of generated code is suppressed, for example, the transition shown in FIG. 8 is performed, and CPB underflow is suppressed. Is done.
- FIG. 12 is a process flowchart showing a moving picture coding control method according to the third 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 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 CPB underflow has occurred due to encoding of the input picture (step S303). If CPB underflow has occurred, the process proceeds to step S308. Whether CPB underflow has occurred is described in, for example, H.B. It can be determined by a method used in the H.264 standard.
- step S304 it is determined whether or not the encoding of the final picture has been completed. If the encoding has been completed up to the final picture, the encoding process is terminated.
- step S305 it is determined whether encoding of the encoding order picture group has been completed. If not completed, the process returns to step S301 to continue the encoding process for the next picture.
- step S306 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 S306).
- -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 S307 an encoding parameter predetermined according to the retry count is set (step S307), and the process returns to step S301 to perform the encoding process from the first picture in the next encoding order picture group. .
- step S303 When it is detected in step S303 that a CPB underflow has occurred, it is determined whether or not the current retry count value is a predetermined maximum value (step S308). In this case, since the CPB underflow cannot be avoided even if the encoding-order picture group is re-encoded, the encoding is terminated.
- 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 S309). Then, the retry count is increased by 1 (step S310). After that, based on the retry count, change one or more of the two encoding parameters (quantization parameter, prefilter strength) (quantization parameter has a larger step size, and in the case of filter strength, the blurring degree is larger. (Change) (step S311), the process returns to step S302, and the encoding order picture group being encoded is re-encoded.
- the present invention is basically a one-time encoding process, and only when a CPB underflow occurs (for example, an encoding order picture group (for example, GOP) is repeatedly encoded with the generated code amount being reduced in steps until no CPB underflow occurs.
- a CPB underflow for example, an encoding order picture group (for example, GOP)
- encoding is performed with an encoding parameter that suppresses CPB underflow 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 as in the first embodiment.
- the Gaussian filter can be created by sampling the Gaussian distribution expressed by the above-described equation (1) with respect to x and y.
- the type of 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 .
- the encoding method is H.264. It is assumed that encoding according to the H.264 standard is performed. Further, the encoding order picture group is GOP, and FIG. 5 shows a conceptual diagram of GOP when encoding. As in the first embodiment, 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. 13 shows an apparatus configuration example according to the third embodiment of the present invention.
- the input buffer 310 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 320. Furthermore, when receiving information (retry information) indicating that CPB underflow occurs and re-encoding from the CPB management unit 340, which will be described later, the input buffer 310 receives video from the first picture of the GOP being encoded. The signal is output again to the encoding unit 320. When the GOP encoding is completed without receiving the retry information, the input buffer 310 discards the stored video signal of the GOP.
- retry information information indicating that CPB underflow occurs and re-encoding from the CPB management unit 340
- 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 code amount (code amount information) generated when the input video signal is encoded is output to the CPB management unit 340. Furthermore, when receiving the retry information from the CPB management unit 340, the encoding unit 320 receives the video signal from the first picture of the GOP being encoded again from the input buffer 310 and re-encodes it from the parameter adjustment unit 370. Since the encoding parameter for encoding is input, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 330 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 CPB management unit 340, the output buffer 330 stores the GOP being encoded. Discard the encoded stream.
- the CPB management unit 340 uses the code amount information input from the encoding unit 320 to obtain the remaining code amount of the CPB that changes with time. That is, the remaining code amount of CPB shown in the conceptual diagram of FIG. 1 is obtained.
- retry information is output to the input buffer 310, the encoding unit 320, the retry count management unit 350, and the output buffer 330 to notify that CPB underflow has occurred.
- the CPB state prediction unit 360 is notified of CPB residual code amount information.
- the retry count management unit 350 When the retry count management unit 350 receives the retry information from the CPB management unit 340, the retry count management unit 350 adds 1 to the current retry count value and notifies the parameter adjustment unit 370 of the updated retry count.
- the parameter adjustment unit 370 is notified of the retry count. However, if the parameter change presence / absence information notified from the CPB state prediction unit 360 indicates “no parameter change”, even if the retry count is 1 or more, 1 is not subtracted from the retry count. Further, even when the retry count is 0, the current retry count value is notified to the parameter adjustment unit 370 without subtracting 1 from it.
- the parameter adjustment unit 370 When the parameter adjustment unit 370 receives the retry count from the retry count management unit 350, the parameter adjustment unit 370 inputs an encoding parameter determined according to the retry count to the encoding unit 320. As a result, the encoding unit 320 performs encoding using an encoding parameter in which the amount of generated code decreases as the number of repetitions of re-encoding increases for the same GOP.
- this embodiment introduces the concept of retry count, which increases when re-encoding occurs and decreases when GOP encoding is completed, and is managed by the retry count management unit 350.
- 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 321 applies the pre-filter strength corresponding to the default encoding parameter to the encoding target picture.
- the filtering process is applied, and the DCT coefficient generated in this picture is quantized by the quantization unit 322 with the quantization parameter according to the default coding 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 CPB management unit 340 calculates the CPB residual code amount for the picture based on the code amount information input from the encoding unit 320. In this example, no CPB underflow occurs, so no retry information is output. (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). Alternatively, if the encoding target picture is the last picture of the GOP, the output buffer 330 outputs the stored encoded stream, and the input buffer 310 discards the stored picture, and the first GOP of the next GOP is output. The process proceeds to a picture encoding process (S305 to S307).
- the CPB management unit 340 transmits the CPB remaining code amount information to the CPB state prediction unit when the GOP encoding is completed. 360 is notified.
- the CPB state prediction unit 360 determines whether or not the CPB remaining code amount is larger than a predetermined threshold, and if so, notifies the retry count management unit 350 that the coding parameter is changed as parameter change presence / absence information.
- the retry count management unit 350 is notified that the coding parameter is not changed as the parameter change presence / absence information.
- the retry count management unit 350 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 (S306).
- 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 350 changes the retry count according to the notification of the parameter change presence / absence information from the CPB state prediction unit 360 and notifies the parameter adjustment unit 370 of the changed retry count.
- the parameter adjustment unit 370 sets an encoding parameter corresponding to the notified retry count in the encoding unit 320, and starts encoding the first picture of the next GOP.
- the input buffer 310 stores the picture and inputs the picture to the encoding unit 320 as an encoding target picture (S301). Then, the encoding unit 320 encodes the picture, outputs the encoded stream to the output buffer 330 (the output buffer 330 does not output the encoded stream but stores it), and sends it to the CPB management unit 340 related to the picture.
- the code amount information is output (S302).
- an encoding parameter corresponding to retry count 1 is used.
- the CPB management unit 340 calculates the remaining CPB code amount for the picture based on the code amount information input from the encoding unit 320. As a result, when the CPB management unit 340 detects a CPB underflow for the picture, the CPB management unit 340 outputs retry information to the encoding unit 320, the retry count management unit 350, the input buffer 310, and the output buffer 330. (S303).
- the input buffer 310 Since the current retry count is 1 and has not reached the upper limit of 3 (S308), the input buffer 310 outputs the accumulated first picture of the GOP being encoded to the encoding unit 320 (S309). ). On the other hand, the retry count is increased by 1 in the retry count management unit 350, and the retry count having a value of 2 is output to the parameter adjustment unit 370 (S310).
- the parameter adjustment unit 370 reads the encoding parameter when the retry count is 2 from the encoding parameter table, and sets the encoding parameter in the encoding unit 320 (S311).
- the output buffer 330 discards the encoded stream of the GOP being encoded.
- the encoding unit 320 unless a CPB underflow occurs, GOP pictures are sequentially input from the input buffer 310 and encoded.
- the retry count is incremented by 1 and becomes 3 by the same processing as described above.
- the CPB management unit 340 notifies the CPB state prediction unit 360 of information on the remaining CPB code amount.
- the CPB state prediction unit 360 notifies the retry count management unit 350 that the parameter change presence / absence information is “changed” when the CPB state residual code amount is equal to or larger than a predetermined threshold, and “no change” otherwise. To do.
- the retry count is reduced by 1 by the retry count management unit 350, the retry count becomes 2, and the encoding of the next GOP proceeds.
- the operations of the input buffer 310 and the output buffer 330 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.
- Fig. 11 shows a conceptual diagram of retry count and coding parameter transition in the case 2 example.
- the second GOP2 is encoded with the retry count being 1
- a CPB underflow has occurred in the encoding of the sixth picture.
- the retry count is set to 2
- FIG. 8 shows a conceptual diagram of the transition of the remaining CPB code amount when re-encoding is performed.
- the bold line represents the CPB residual code amount after re-encoding.
- the pre-filter increases the degree of blurring and the quantization parameter is larger than the default encoding parameter, so that the amount of generated code is suppressed, for example, the transition shown in FIG. 8 is performed, and CPB underflow is suppressed. Is done.
- FIG. 14 is a process flowchart showing a moving picture coding control method according to the fourth 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 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 CPB underflow has occurred due to encoding of the input picture (step S403). If CPB underflow has occurred, the process proceeds to step S411. Whether CPB underflow has occurred is described in, for example, H.B. It can be determined by a method used in the H.264 standard.
- step S404 it is determined whether or not the encoding of the final picture has been completed. If the encoding has been completed up to the final picture, the encoding process is terminated.
- step S405 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 S406). This is because, in step S409, which will be described later, when the CPB residual code amount is less than the predetermined threshold, the retry point remains set at the head of the previous coding-order picture group. This is a process for updating the retry point after confirming that no underflow occurs. If a retry point is set in step S410, the retry point is reset at the same position, but there is no inconvenience in processing. Thereafter, the process returns to step S401, and the encoding of the next picture proceeds.
- step S407 it is next determined whether or not the encoding order picture group has been encoded. If not completed, the process returns to step S401, and the encoding process continues 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 S408).
- step S409 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 greater than a predetermined threshold, the retry point is set to the first I picture of the next coding order picture group (step S410). Thereafter, the process returns to step S401, 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 S401 to proceed to the encoding of the next encoding order picture group.
- step S431 If it is detected in step S403 that a CPB underflow has occurred, it is determined whether or not the current coding-order picture group has been re-encoded (retry has been completed) (step S411). If the retry has been completed, CPB underflow cannot be avoided even if the encoding-order picture group is re-encoded, and therefore encoding is terminated. If the retry has not been completed, the picture at the retry point is set as an encoding target in order to re-encode the current encoding-order picture group (step S412).
- step S43 the quantization parameter has a larger step size, and in the case of the filter strength, the blurring degree is changed to be larger.
- the encoding order picture group (for example, GOP) is encoded twice only when CPB underflow occurs.
- encoding is performed with an encoding parameter that suppresses CPB underflow. Only when a CPB underflow occurs, only the coding order picture group in which it has occurred is re-encoded (in some cases, the previous coding order picture group may be re-encoded. ), Suppresses 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. 15 is a process flowchart showing a modification of the moving picture coding control method according to the fourth embodiment of the present invention.
- the present invention can also be implemented by replacing the processing in step S408 shown in FIG. 14 with the processing in steps S481 to S483 shown in FIG. Processes other than step S408 are substantially the same as those in FIG.
- step S481 it is determined whether the encoding parameter has been changed by retry. If it has not been changed by the retry, the process proceeds to step S409. If it 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 first threshold (step S482). If it is less than the predetermined threshold value, the encoding parameter remains in the state used in re-encoding, and the encoding parameter is returned to the original default encoding parameter only when it is equal to or greater than the predetermined threshold value (step S483).
- step S409 it is determined whether or not the CPB remaining code amount is equal to or larger than a predetermined second threshold.
- This process and the process of step S410 are the same as the processes of steps S409 and S410 shown in FIG. Note that the first threshold value and the second threshold value may be the same value or different values.
- 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 as in the first embodiment.
- the Gaussian filter can be created by sampling the Gaussian distribution expressed by the above-described equation (1) with respect to x and y.
- the type of 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 .
- Encoding is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP, and a conceptual diagram of the GOP when encoding is shown in FIG. As in the first embodiment, 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. 16 shows an apparatus configuration example of the fourth embodiment of the present invention.
- the input buffer 410 accumulates the input video signal and outputs the video signal to be encoded to the encoding unit 420. Further, when receiving information (retry information) indicating that CPB underflow occurs and re-encoding is performed from the CPB management unit 440 described later, the input buffer 410 starts from the first picture of the GOP set as the retry point. The video signal is output again to the encoding unit 420. When retry point information is input from the retry point management unit 460, the input buffer 410 discards the stored GOP video signal before the retry point.
- 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 code amount (code amount information) generated when the input video signal is encoded is output to the CPB management unit 440. Furthermore, when receiving the retry information from the CPB management unit 440, the encoding unit 420 receives the video signal from the first picture of the GOP indicated by the retry point again from the input buffer 410 and re-encodes it from the parameter adjustment unit 470. Since the encoding parameter for encoding is input, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 430 Based on the retry point information from the retry point management unit 460, the output buffer 430 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 CPB management unit 440, the output buffer 430 discards the encoded stream stored for the GOP being encoded.
- the CPB management unit 440 uses the code amount information input from the encoding unit 420 to obtain the remaining code amount of the CPB that changes with time. That is, the remaining code amount of CPB shown in the conceptual diagram of FIG. 1 is obtained.
- retry information is output to the input buffer 410, encoding unit 420, parameter adjustment unit 470, and output buffer 430 to notify that CPB underflow has occurred.
- CPB management section 440 outputs the CPB remaining code amount at the time when the GOP encoding is completed to CPB state prediction section 450.
- the CPB state prediction unit 450 determines whether or not the CPB residual code amount is larger than a predetermined threshold value.
- the retry point management unit 460 determines the retry point of the next GOP as the head of the GOP. Information indicating that this is an I picture is notified as retry point change presence / absence information.
- the value is smaller than the threshold, information indicating 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 is notified as retry point change presence / absence information.
- the retry point management unit 460 notifies the input buffer 410 of the retry point.
- the input buffer 410 is notified that the retry point is set as the first picture of the GOP currently encoded from the encoding of the next picture.
- the retry point is notified to the input buffer 410 and the output buffer 430.
- notification information is referred to as retry point information.
- the input buffer 410 inputs a video signal from the picture based on the retry point information to the encoding unit 420 at the time of re-encoding, and the output buffer 430 is determined to output based on the retry point information. Output only stream.
- the parameter adjustment unit 470 When the parameter adjustment unit 470 receives retry information from the CPB management unit 440, the parameter adjustment unit 470 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.
- 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.
- a default encoding parameter is 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 parameter, and a DCT coefficient generated in the main picture is generated.
- the CPB management unit 440 calculates the CPB residual code amount for the picture based on the code amount information input from the encoding unit 420. In this example, no CPB underflow occurs, so no retry information is output. (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).
- the retry point management unit 460 sets the first picture (I picture) of GOP1 as a retry point (S406), and then the encoding unit 420 continues with the next picture.
- the encoding of the picture is advanced.
- the parameter adjustment unit 470 changes the encoding parameter to the default encoding parameter when the encoding parameter for re-encoding is used for re-encoding. (S408).
- the CPB management unit 440 outputs CPB residual code amount information to the CPB state prediction unit 450, and the CPB state prediction unit 450 determines whether the CPB residual code amount is larger than a predetermined threshold (S409).
- the determination result is notified to the retry point management unit 460 as the above-described retry point change presence / absence information.
- the retry point management unit 460 notifies the input buffer 410 that the retry point is the first picture of GOP1 as retry point information. Thereafter, the process proceeds to the encoding process of the first I picture of GOP2 (S402).
- the retry point management unit 460 When no CPB underflow occurs in the encoding of the I picture (S403), the retry point management unit 460 includes the input buffer 410 and the output buffer. 430 is notified that the retry point is the first picture of GOP2 (S406). That is, when re-encoding occurs in subsequent GOP2 pictures, re-encoding is performed from the first picture of GOP2.
- retry change presence / absence information indicating that the retry point is to be changed is output from the CPB state prediction unit 450 to the retry point management unit 460. Then, the retry point management unit 460 notifies the input buffer 410 that the retry point is the first picture of GOP2 as retry point information (S410). In this case, even if CPB underflow occurs in any picture of GOP2 next, re-encoding is performed from the first picture of GOP2.
- the input buffer is based on the retry information from the CPB management unit 440.
- 410 sequentially inputs pictures into the encoding unit 420 from the first picture of GOP1, and the encoding unit 420 performs re-encoding.
- the encoding parameter for re-encoding set from the parameter adjustment unit 470 is used (S413).
- the pre-filter unit 421 applies a pre-filtering process to the encoding target picture with a pre-filter strength corresponding to the encoding parameter for re-encoding (a blurring degree is larger than the default encoding parameter),
- 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 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.
- FIG. 7 shows a conceptual diagram of changing the encoding parameter when re-encoding is performed on an intermediate picture of GOP2.
- CPB underflow has occurred in the encoding of the sixth picture of GOP2. Therefore, the encoding parameter for re-encoding that suppresses the generated code amount is set, Re-encoding is performed from the first I picture of GOP2. Since the occurrence of CPB underflow is suppressed by the re-encoding, in the next GOP3 encoding, the re-encoding encoding parameter is returned to the default encoding parameter, and the encoding process is continued.
- FIG. 8 shows a conceptual diagram of the transition of the remaining CPB code amount when re-encoding is performed. Similar to the first to third embodiments, the bold line represents the CPB residual code amount after re-encoding.
- the pre-filter increases the degree of blurring and the quantization parameter is larger than the default encoding parameter, so that the amount of generated code is suppressed, for example, the transition shown in FIG. 8 is performed, and CPB underflow is suppressed. Is done.
- FIG. 17 is a process flowchart showing a moving picture coding control method according to the fifth embodiment of the present invention.
- 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 (S500).
- the picture next to 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 the encoding target (step S501).
- the input picture set as the encoding target is defined as H.264.
- H.264 and other predetermined encoding methods are used (step S502).
- CPB underflow has occurred due to the encoding of the input picture (step S503). If CPB underflow has occurred, the process proceeds to step S507.
- Whether CPB underflow has occurred is described in, for example, H.B. It can be determined by a method used in the H.264 standard.
- step S504 it is determined whether or not the encoding of the last picture has been completed. If the encoding has been completed up to the last picture, the encoding process is terminated.
- step S505 it is determined whether or not the encoding order picture group has been encoded. If not completed, the process returns to step S501 to continue the encoding process 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 ( Returning to step S506) and step S501, the encoding process is performed from the head picture of the next encoding order picture group.
- step S507 it is determined whether the current picture being encoded has been re-encoded (retry has been completed) (step S507). If the retry has been completed, the CPB underflow cannot be avoided even if the pictures in the coding order picture group are re-encoded, and thus the encoding is terminated. If the retry has not been completed, a retry point is set for re-encoding 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 S500 is set as an encoding target (step S508).
- step S509 one or more of the two encoding parameters (quantization parameter, prefilter strength) are changed (the quantization parameter has a larger step size, and in the case of filter strength, the blurring degree is changed to be larger) (step S509). ), The process returns to step S502, and re-encoding is performed from the pictures in the encoding order picture group set as the retry point.
- the above re-encoding process unlike the conventional technique b in which all frames of the input video are encoded twice, only a plurality of pictures in the encoding-order picture group (for example, GOP) is generated only when CPB underflow occurs. Is encoded twice.
- encoding is performed with an encoding parameter that suppresses CPB underflow. Only when the CPB underflow occurs, the CPB underflow is suppressed by re-encoding only a plurality of pictures in the coding order picture group in which the CPB underflow has occurred. 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. Further, the memory required as the input buffer and the output buffer is only required for the predetermined number of pictures, and the memory can be reduced.
- FIG. 18 is a process flowchart showing a modification of the moving picture coding control method according to the fifth embodiment of the present invention.
- the present invention can be implemented by replacing the processing in step S506 shown in FIG. 17 with the processing in steps S561 to S563 shown in FIG. Processes other than step S506 are the same as those in FIG.
- step S561 it is determined whether the encoding parameter has been changed by retry. If it has not been changed by retry, the process returns to step S501 in FIG. If it 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 S562). If it is less than the predetermined threshold, the encoding parameter remains in the state used for re-encoding, and the encoding parameter is returned to the original default encoding parameter only when it is equal to or greater than the predetermined threshold (step S563). Thereafter, the process returns to step S501 in FIG. 17, and the process proceeds to encoding of the next encoding order picture group.
- 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 of CPB underflow increases in the coding of pictures. In the process of FIG. 18, when the CPB residual code amount is small, the encoding parameter is not changed. Therefore, compared to the process of FIG. 17, the occurrence of re-encoding is suppressed in encoding of the next encoding order picture group. 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 as in the first embodiment.
- the Gaussian filter can be created by sampling the Gaussian distribution expressed by the above-described equation (1) with respect to x and y.
- the type of 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 .
- Encoding is H.264. It is assumed that encoding according to the H.264 standard is performed.
- the encoding order picture group is GOP, and a conceptual diagram of the GOP when encoding is shown in FIG. As in the first embodiment, 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. 19 shows an apparatus configuration example according to the fifth embodiment of the present invention.
- the maximum inter-picture distance determination unit 600 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 time of re-encoding based on this.
- the input video signal of the GOP being encoded is stored in the input buffer 510, and the encoded stream of the GOP being encoded is stored in the output buffer 530.
- the maximum inter-picture distance determination unit 600 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 value of the maximum inter-picture distance in the worst case of the input buffer 510 and the output buffer 530.
- 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 510 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 530 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. 20 shows a conceptual diagram for explaining the required memory amount.
- the GOP has a 10-picture configuration and the maximum inter-picture distance is 6 as shown in FIG.
- the maximum number of pictures to be held in the input buffer 510 is seven.
- the decoded images of the first I picture and the next P picture also need to be held in the memory as reference images.
- the maximum inter-picture distance is equal to the GOP length
- the number of pictures to be held in 510 is reduced by three. That is, the smaller the maximum inter-picture distance, the larger the reference image memory amount.
- the required memory amount decreases when the maximum inter-picture distance is reduced. .
- a motion vector of a reference image may be referred to, and thus a memory for this 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 600 is not notified of the amount of available memory from the outside and the maximum inter-picture distance is calculated. You may make it give to the distance determination part 600 between pictures.
- the maximum inter-picture distance determination unit 600 notifies the retry point management unit 560 of the determined maximum inter-picture distance information.
- the input buffer 510 stores the input video signal and outputs the video signal to be encoded to the encoding unit 520. Further, the input buffer 510 receives the retry point notified from the retry point management unit 560 when receiving information (retry information) indicating that CPB underflow occurs and re-encoding is performed from the CPB management unit 540 described later. The video signal from the picture is output to the encoding unit 520 again. Further, when the retry point information is notified from the retry point management unit 560, the input buffer 510 discards the stored video signal data corresponding to the pictures before the retry point.
- the encoding unit 520 encodes the video signal input from the input buffer 510 and outputs the encoded stream to the output buffer 530.
- the encoding unit 520 outputs the code amount (code amount information) generated when the input video signal is encoded to the CPB management unit 540 when the encoding of the picture is completed, and the retry point.
- Information indicating that the encoding of the picture has been completed is output to the management unit 560.
- the encoding unit 520 receives retry information from the CPB management unit 540, the video signal from the picture of the retry point in the GOP being encoded is input again from the input buffer 510 and also from the parameter adjustment unit 550. Since the encoding parameter for re-encoding is input, re-encoding is performed using the input encoding parameter for re-encoding.
- the output buffer 530 stores the encoded stream that is the GOP encoding result, and when the retry point information is notified from the retry point management unit 560, the output buffer 530 corresponds to the pictures before the retry point stored so far.
- the encoded stream is output and the data is removed from the output buffer 530.
- the encoded stream stored for the GOP being encoded is discarded.
- the CPB management unit 540 uses the code amount information input from the encoding unit 520 to obtain the remaining code amount of the CPB that changes with time. That is, the remaining code amount of CPB shown in the conceptual diagram of FIG. 1 is obtained.
- retry information is output to the input buffer 510, encoding unit 520, parameter adjustment unit 550, and output buffer 530 to notify that CPB underflow has occurred.
- the parameter adjustment unit 550 When the parameter adjustment unit 550 receives retry information from the CPB management unit 540, the parameter adjustment unit 550 inputs the encoding parameter for re-encoding to the encoding unit 520 as described above. As a result, the encoding unit 520 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 560 based on the encoding complete picture information and the maximum inter-picture distance information, specifies retry point information indicating where the retry point becomes when a CPB underflow occurs in encoding the next picture. This is notified to the input buffer 510 and the output buffer 530.
- a process for encoding a certain GOP will be described in three cases as follows.
- a default encoding parameter is used, and a filtering process by the prefilter unit 521 is applied to a picture to be encoded with a prefilter strength corresponding to the default encoding parameter, and a DCT coefficient generated in the main picture is generated.
- the CPB management unit 540 calculates the remaining CPB code amount for the picture based on the code amount information input from the encoding unit 520. In this example, no CPB underflow occurs, so no retry information is output. (S503). If the encoding target picture is the last picture in the input video signal, the output buffer 530 outputs the stored encoded stream, and the encoding process is completed (S504). Alternatively, if the encoding target picture is the last picture of the GOP, the output buffer 530 outputs the stored encoded stream, and the input buffer 510 discards the stored picture, and the first GOP of the next GOP is output. The process proceeds to picture coding processing (S505). 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 (S506).
- the CPB management unit 540 calculates the CPB residual code amount for the picture based on the code amount information input from the encoding unit 520. As a result, when the CPB management unit 540 detects CPB underflow for the picture, the CPB management unit 540 outputs retry information to the encoding unit 520, parameter adjustment unit 550, input buffer 510, and output buffer 530 ( S503).
- the input buffer 510 When retry has not yet occurred for the GOP being encoded (S507), the input buffer 510 outputs the picture at the position indicated by the retry point in the GOP being encoded to the encoder 520 ( In step S508, the parameter adjustment unit 550 outputs the encoding parameter for re-encoding to the encoding unit 520 (S509). Furthermore, the output buffer 530 discards the encoded stream of the GOP being encoded. Then, the encoding unit 520 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.
- the pre-filtering process by the filter unit 521 is applied, and the DCT coefficient generated in this picture is quantized with a quantization parameter (a quantization step size is larger than the default encoding parameter) according to the encoding parameter for re-encoding. Quantized by the unit 522.
- the pictures of the GOP are sequentially input from the input buffer 510 to the encoding unit 520, and the encoding unit 520 performs the encoding process.
- the encoded stream of the GOP is output from the output buffer 530, and the encoding unit 520 sets the encoding parameter as a default encoding parameter ( S506), 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 the case 1 described above.
- Fig. 7 shows a conceptual diagram of changing the encoding parameters when re-encoding is performed. Similar to the first embodiment, in the example of FIG. 7, since CPB underflow occurred in the encoding of the sixth picture of the second GOP2, a re-encoding encoding parameter that suppresses the generated code amount is set. Thus, re-encoding is performed from the first I picture of GOP2 within the range of the maximum inter-picture distance. Since the occurrence of CPB underflow is suppressed by the re-encoding, in the next GOP3 encoding, the re-encoding encoding parameter is returned to the default encoding parameter, and the encoding process is continued.
- FIG. 8 shows a conceptual diagram of the transition of the remaining CPB code amount when re-encoding is performed.
- the bold line represents the CPB residual code amount after re-encoding.
- the pre-filter increases the degree of blurring and the quantization parameter is larger than the default encoding parameter, so that the amount of generated code is suppressed, for example, the transition shown in FIG. 8 is performed, and CPB underflow is suppressed. Is done.
- FIG. 21 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 this embodiment will be described as “Case A”.
- the picture that starts re-encoding when a CPB underflow occurs can always be the first picture of a coding-order picture group (for example, GOP). This is called “Case B”.
- the currently encoded picture is the ninth P picture of GOP2 ′ as shown in FIG. 21, and the maximum inter-picture distance is “5”.
- the input buffer 510 corresponding to these pictures and Data in the output buffer 530 need not be retained (can be discarded).
- case B data corresponding to these pictures are held in the input buffer 510 and the output buffer 530 until encoding of GOP2 from the first picture of GOP2 ′ is completed. This increases the amount of memory required.
- the memory amount can be reduced as compared with Case B.
- the video encoding control processing according to the first to fifth embodiments described above can be realized by a computer and a software program, and the program can be recorded on a computer-readable recording medium. It is also possible to provide through.
- the present invention can be applied to a moving picture coding technique for coding a video signal, and is coded so as to prevent underflow of a virtual buffer such as a coded picture buffer in a virtual decoder. Image quality can be improved.
Abstract
Description
本願は、2010年5月7日に日本に出願された特願2010-106851号、特願2010-106852号、特願2010-106853号、特願2010-106854号および特願2010-106855号に基づき優先権を主張し、そ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。従い,1パス符号化でCPBアンダーフローを抑制しようとした場合,必要以上に発生符号量を抑えてしまい,必要以上に大きく画質を劣化させてしまうことがある。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,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。推定された複雑度と比較して,GOPの残りの映像が複雑でない場合には,必要以上に符号量を抑えてしまい画質劣化を招く問題があることが分かる。
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。すなわち,各フレームの複雑度が分かっているため,CPBアンダーフローが生じる場合にのみ割り当て符号量を修正することが可能となり,結果として従来技術aと比較して画質劣化を抑えつつCPBアンダーフローを抑制できる。しかしながら,この方法では,入力映像の全フレームを2回符号化する必要があるため,演算量が多くなるという問題がある。
例えば,符号化順ピクチャ群を13ピクチャ構成とした場合には,図2Cに示すような符号化順で連続した13ピクチャが本発明でいう符号化順ピクチャ群となる。さらに、図2Dは,符号化順ピクチャ群を2GOP分の20ピクチャ構成とした場合の例を示している。
メータの変化量が大き過ぎると無駄に画質を劣化させることになる。
メータの変化量が大き過ぎると無駄に画質を劣化させることになる。
(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CPBアンダーフローが発生しなかった場合,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:符号化中の符号化順ピクチャ群に含まれること。
・条件2:CPBアンダーフローが生じ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,CPBアンダーフローが生じたピクチャから最も遠いピクチャであること。
<第1の実施例>
図3は,本発明の第1の実施例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(1)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,例えば以下の参考文献1に記載されている。
〔参考文献1〕: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,本発明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CPBアンダーフローが発生しなかった。
・[ケース2]:GOPの符号化においてCPBアンダーフローが発生し,再符号化で回避できた。
・[ケース3]:GOPの符号化においてCPBアンダーフローが発生し,再符号化でも回避できなかった。
まず,GOPの符号化においてCPBアンダーフローが発生し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は出力せず,蓄積する),当該ピクチャに関するCPB管理部140に符号量情報を出力する(S102)。
次に,GOPの符号化においてCPBアンダーフローが発生し,再符号化で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は出力せず,蓄積する),当該ピクチャに関するCPB管理部140に符号量情報を出力する(S102)。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CPBアンダーフローが発生し,再符号化でも回避できなかった場合のケース3について説明する。この場合,CPB管理部140によりCPBアンダーフローが検知され,GOPの再符号化を行う動作はケース2と同様である。このGOPの再符号化中にCPBアンダーフローが生じた場合,符号化を完了する(S107)。なお,符号化を完了するのでなく,コマ落としを許容し,符号化を完了しないで,CPBアンダーフローが生じたピクチャの符号化データを破棄し,次のピクチャを符号化するように処理してもよい。
<第2の実施例>
・[ケース1]:GOPの符号化においてCPBアンダーフローが発生しなかった。
・[ケース2]:GOPの符号化において複数回CPBアンダーフローが発生し,再符号化で回避できた。
・[ケース3]:GOPの符号化において複数回CPBアンダーフローが発生し,リトライカウントが上限値に達して再符号化でも回避できなかった。
まず,GOPの符号化においてCPBアンダーフローが発生し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は出力せず,蓄積する),当該ピクチャに関するCPB管理部240に符号量情報を出力する(S202)。
次に,GOPの符号化において複数回CPBアンダーフローが発生し,再符号化で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CPBアンダーフローが発生し,リトライカウントが上限値に達して再符号化でも回避できなかった場合のケース3について説明する。あるGOPを符号化中に,ケース2の場合と同様に,リトライカウントが3に達したとする。さらに,同じGOPの符号化において,CPB管理部240によりCPBアンダーフローが検知された場合(S203),リトライカウント管理部250でリトライカウントが上限値に達していることが検知され(S208),符号化が完了する。なお,このような場合に,符号化を完了するのでなく,コマ落としを許容し,符号化を完了しないで,CPBアンダーフローが生じたピクチャの符号化データを破棄し,次のピクチャを符号化するように処理してもよい。
<第3の実施例>
・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。
・[ケース1]:GOPの符号化においてCPBアンダーフローが発生しなかった。
・[ケース2]:GOPの符号化において複数回CPBアンダーフローが発生し,再符号化で回避できた。
・[ケース3]:GOPの符号化において複数回CPBアンダーフローが発生し,リトライカウントが上限値に達して再符号化でも回避できなかった。
まず,GOPの符号化においてCPBアンダーフローが発生し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は出力せず,蓄積する),当該ピクチャに関するCPB管理部340に符号量情報を出力する(S302)。
次に,GOPの符号化において複数回CPBアンダーフローが発生し,再符号化で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CPBアンダーフローが発生し,リトライカウントが上限値に達して再符号化でも回避できなかった場合のケース3について説明する。あるGOPを符号化中に,ケース2の場合と同様に,リトライカウントが3に達したとする。さらに,同じGOPの符号化において,CPB管理部340によりCPBアンダーフローが検知された場合(S303),リトライカウント管理部350でリトライカウントが上限値に達していることが検知され(S308),符号化が完了する。なお,このような場合に,符号化を完了するのでなく,コマ落としを許容し,符号化を完了しないで,CPBアンダーフローが生じたピクチャの符号化データを破棄し,次のピクチャを符号化するように処理してもよい。
<第4の実施例>
・[ケース1]:GOP1の符号化においてCPBアンダーフローが発生しないで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CPBアンダーフローが発生しなかった。
・[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CPBアンダーフローが発生し,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CPBアンダーフローが発生し,再符号化が必要になった。
・[ケース4]:GOP2の符号化においてCPBアンダーフローが発生し,再符号化でも回避できなかった。
まず,GOP1の符号化においてCPBアンダーフローが発生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は出力せず,蓄積する),当該ピクチャに関するCPB管理部440に符号量情報を出力する(S402)。
次に,GOP2の先頭ピクチャの符号化においてCPBアンダーフローが発生し,再符号化で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460は,入力バッファ410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CPBアンダーフローが発生し,再符号化が必要になった例を説明したが,GOP2の先頭ピクチャ以外のピクチャでCPBアンダーフローが生じた場合には,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の符号化においてCPBアンダーフローが発生し,再符号化でも回避できなかった場合のケース4について説明する。この場合,CPB管理部440によりCPBアンダーフローが検知され,GOP2の再符号化を行う動作は,前のケース3と同様である。このGOP2の再符号化中にCPBアンダーフローが生じた場合,符号化を完了する(S411)。なお,符号化を完了するのでなく,コマ落としを許容し,符号化を完了しないで,CPBアンダーフローが生じたピクチャの符号化データを破棄し,次のピクチャを符号化するように処理してもよい。
<第5の実施例>
一方で,出力バッファ530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CPBアンダーフローが発生しなかった。
・[ケース2]:GOPの符号化においてCPBアンダーフローが発生し,再符号化で回避できた。
・[ケース3]:GOPの符号化においてCPBアンダーフローが発生し,再符号化でも回避できなかった。
まず,GOPの符号化においてCPBアンダーフローが発生し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510に入力されると,入力バッファ510は当該ピクチャを蓄積するとともに,符号化部520に当該ピクチャを符号化対象ピクチャとして入力する(S501)。そして,符号化部520は当該ピクチャを符号化し,出力バッファ530に符号化ストリームを出力するとともに(出力バッファ530は当該符号化ストリームは出力せず,蓄積する),当該ピクチャに関するCPB管理部540に符号量情報を出力する。また,リトライポイント管理部560に,符号化完了ピクチャ情報を出力する(S502)。
次に,GOPの符号化においてCPBアンダーフローが発生し,再符号化で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510に入力されると,入力バッファ510は当該ピクチャを蓄積するとともに,符号化部520に当該ピクチャを符号化対象ピクチャとして入力する(S501)。そして,符号化部520は当該ピクチャを符号化し,出力バッファ530に符号化ストリームを出力するとともに(出力バッファ530は当該符号化ストリームは出力せず,蓄積する),当該ピクチャに関するCPB管理部540に符号量情報を出力する(S502)。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CPBアンダーフローが発生し,再符号化でも回避できなかった場合のケース3について説明する。この場合,CPB管理部540によりCPBアンダーフローが検知され,GOPの再符号化を行う動作はケース2と同様である。このGOPの再符号化中にCPBアンダーフローが生じた場合,符号化を完了する(S507)。なお,符号化を完了するのでなく,コマ落としを許容し,符号化を完了しないで,CPBアンダーフローが生じたピクチャの符号化データを破棄し,次のピクチャを符号化するように処理してもよい。
120,220,320,420,520 符号化部
121,221,321,421,521 プレフィルタ部
122,222,322,422,522 量子化部
130,230,330,430,530 出力バッファ
140,240,340,440,540 CPB管理部
150,260,370,470,550 パラメータ調整部
250,350, リトライカウント管理部
360,450, CPB状態予測部
460,560 リトライポイント管理部
600 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,
前記各ピクチャの符号化において発生した符号量情報をもとに,前記仮想バッファにアンダーフローが発生したか否かを検査するステップと,
前記仮想バッファにアンダーフローが発生した場合に,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,符号化中の前記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、前記仮想バッファにアンダーフローが発生した場合に,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の最終のピクチャの符号化が完了するまで,前記仮想バッファにアンダーフローが発生しなかった場合に,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地露来カウントが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,前記仮想バッファにアンダーフローが発生しなかった場合に,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,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のピクチャ数で構成され,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,
前記各ピクチャの符号化において発生した符号量情報をもとに,前記仮想バッファにアンダーフローが発生したか否かを検査するステップと,
前記仮想バッファにアンダーフローが発生した場合に,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前記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が前記仮想バッファのアンダーフローを生じさせないで完了した後に,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,
前記各ピクチャの符号化において発生した符号量情報をもとに,前記仮想バッファにアンダーフローが発生したか否かを検査するステップと,
前記仮想バッファにアンダーフローが発生した場合に,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,符号化中の前記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に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,前記仮想バッファにアンダーフローが発生しなかった場合に,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に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仮想バッファにアンダーフローが発生しなかった場合に,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,
前記各ピクチャの符号化において発生した符号量情報をもとに,前記仮想バッファにアンダーフローが発生したか否かを検査し,前記仮想バッファにアンダーフローが発生したことを検出した場合にリトライ情報を出力するバッファ管理部と,
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,符号化中の前記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に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に記載の動画像符号化装置において、
前記仮想バッファにアンダーフローが発生しないで,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した場合に,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,
前記各ピクチャの符号化において発生した符号量情報をもとに,前記仮想バッファにアンダーフローが発生したか否かを検査し,前記仮想バッファにアンダーフローが発生したことを検出した場合にリトライ情報を出力するバッファ管理部と,
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,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が前記仮想バッファのアンダーフローを生じさせないで完了した後に,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,
前記各ピクチャの符号化において発生した符号量情報をもとに,前記仮想バッファにアンダーフローが発生したか否かを検査し,前記仮想バッファにアンダーフローが発生したことを検出した場合にリトライ情報を出力するバッファ管理部と,
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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BR112012028184A2 (pt) | 2016-08-02 |
TWI483617B (zh) | 2015-05-01 |
EP2568705A1 (en) | 2013-03-13 |
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CN102986212A (zh) | 2013-03-20 |
RU2530313C2 (ru) | 2014-10-10 |
JP5295429B2 (ja) | 2013-09-18 |
RU2012146537A (ru) | 2014-06-20 |
EP2568705B1 (en) | 2018-09-26 |
EP2568705A4 (en) | 2014-04-09 |
US20130051456A1 (en) | 2013-02-28 |
ES2703005T3 (es) | 2019-03-06 |
KR20130028093A (ko) | 2013-03-18 |
US9179165B2 (en) | 2015-11-03 |
CN102986212B (zh) | 2015-11-25 |
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