JP3721972B2 - MPEG image data recording method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an MPEG image data recording method for recording MPEG image data, which is image data compressed by an MPEG encoding method, on a recording medium. In particular, an object of the present invention is to provide an MPEG image data recording method capable of realizing seamless reproduction when additionally recorded MPEG image data is reproduced.
[0002]
[Prior art]
First, the conventional MPEG will be briefly described. Since MPEG is described in detail in ISO-IEC11172-2 and ITU-T H.262 / ISO-IEC13818-2, only the outline will be described here. MPEG is the name of the organization that examines video coding standards established in 1988 in ISO / IEC JTC1 / SC2 (International Organization for Standardization / International Electrotechnical Standards Meeting Technical Committee 1 / Technical Committee 2, now SC29) ( Abbreviation for Moving Pictures Expert Group. MPEG1 (MPEG Phase 1) is a standard for storage media of about 1.5 Mbps, and is intended for video compression for low transfer rates of JPEG and ISDN video conferences and videophones for the purpose of still image coding. H.261 (CCITT SGXV, standardized by the current ITU-T SG15), the new technology was introduced for storage media. These were established in August 1993 as ISO / IEC 11172.
[0003]
MPEG is created by combining several technologies. FIG. 5 shows a conventional MPEG encoder, which will be briefly described below. For the input image, the difference between the image decoded by the motion compensation predictor 1 and the input image is taken by the differencer 2 to reduce the time redundant portion.
[0004]
There are three modes of prediction from the past and the future. These can be switched and used for each 16 pixels × 16 pixels MB (macroblock). The prediction direction is determined by the picture type given to the input image. A P picture has two modes: a mode in which encoding is performed by prediction from the past and a mode in which the MB is independently encoded without prediction. In the B picture, there are four modes of prediction from the future, prediction from the past, prediction from both, and independent encoding. An I picture encodes all MBs independently.
[0005]
In motion compensation, the motion region is subjected to pattern matching for each MB, a motion vector is detected with half-pel accuracy, and prediction is performed after shifting by the motion amount. The motion vector has a horizontal direction and a vertical direction, and is transmitted as additional information of the MB together with an MC (Motion Compensation) mode indicating where the motion vector is predicted.
[0006]
A group from an I picture to a picture before the next I picture is called a GOP (Group Of Picture), and when it is used in a storage medium or the like, generally about 15 pictures are used as one GOP.
[0007]
The difference image is subjected to orthogonal transformation in the DCT unit 3. DCT (Discrete Cosine Transform) is an orthogonal transformation that discretely transforms an integral transformation with a cosine function as an integral kernel into a finite space. In MPEG, MB is divided into four and two-dimensional DCT is performed on an 8 × 8 DCT block. In general, video signals have many low-frequency components and few high-frequency components. Therefore, when DCT is performed, coefficients are concentrated in the low frequency range.
[0008]
The image data (DCT coefficient) subjected to DCT is quantized by the quantizer 4. Quantization is a quantized value obtained by multiplying the 8 × 8 two-dimensional frequency called the quantization matrix by the visual characteristic weighted by the value of the quantization scale that multiplies the whole by a scalar, and the DCT coefficient is quantized. Calculate by value. When inverse quantization is performed by the MPEG decoder (decoder), a value approximating the original DCT coefficient is obtained by multiplying by the quantized value.
[0009]
The quantized data is variable length encoded by the VLC unit 5. Among the quantized values, the direct current (DC) component uses DPCM (differential pulse code modulation) which is one of predictive coding. Also, AC (AC) components are zigzag scanned from low to high, with zero run length and effective coefficient value as one event, and Huffman coding assigning codes with short code lengths from those with high appearance probability. Is done.
[0010]
The variable-length encoded data is stored in the temporary buffer 6 and output as encoded data at a predetermined transfer rate. The generated code amount for each macroblock of the output data is transmitted to the code amount controller 21, and the error code amount with respect to the generated code amount with respect to the target code amount is fed back to the quantizer 4 to quantize the scale. The amount of code is controlled by adjusting.
[0011]
The quantized image data is inversely quantized by the inverse quantizer 7, inversely DCTed by the inverse DCT unit 8, temporarily stored in the image memory 10 via the adder 9, and then the motion compensated predictor 1. Are used as reference decoded images for calculating difference images.
[0012]
FIG. 6 shows an MPEG decoder (decoder) for decoding the encoded data encoded in this way.
[0013]
Incoming encoded data (stream) is buffered by the buffer 11, and the data from the buffer 11 is input to the VLD unit 12. The VLD unit 12 performs variable length decoding to obtain a direct current (DC) component and an alternating current (AC) component. The alternating current (AC) component data is arranged in an 8 × 8 matrix in the order of zigzag scan from low to high. This data is input to the inverse quantizer 13 and is inversely quantized by the quantization matrix. The inversely quantized data is input to the inverse DCT unit 14 and subjected to inverse DCT, and output as image data (decoded data). The decoded data is temporarily stored in the image memory 16 and then used as a reference decoded image for calculating a difference image in the motion compensation predictor 17.
[0014]
In the case of video, the encoded bit stream has a variable amount of code for each picture. This is because MPEG uses information conversion such as DCT, quantization, and Huffman coding, and at the same time, it is necessary to adaptively change the amount of code allocated to each picture to improve image quality. This is because the entropy of the encoded image itself changes greatly, such as encoding the input image as it is in some cases and encoding a difference image that is the difference between the predicted images in some cases.
[0015]
In this case, in many cases, the code amount is controlled while allocating the entropy ratio of the image and keeping the limitation of the buffer. The buffer manager monitors the relationship between the generated code amount and the encoding rate, and sets the target code amount so as to be within a predetermined buffer. This value is fed back to the variable length encoder and enters the code amount controller, where the generated code amount is suppressed by increasing the quantized value set in the quantizer or by reducing the quantized value. Or make it smaller.
[0016]
When encoding such variable-length data at a fixed transfer rate (encoding rate), if the maximum buffer amount of the decoder is the upper limit value, the data is input at a constant speed and only a predetermined value is accumulated. Therefore, MPEG is specified to use a model that performs decoding instantaneously at a predetermined time (1 / 29.97 sec unit for NTSC video signals) and encodes the buffer so that neither overflow nor underflow occurs. ing. If this rule (VBV buffer rule) is observed, the rate in the VBV buffer changes locally, but if the observation time is long, it becomes a fixed transfer rate. In MPEG, this is a fixed rate. Defined.
[0017]
In the case of a fixed transfer rate, when the amount of generated code is small, the buffer occupation amount is stuck to the upper limit value. In this case, it is necessary to increase the code amount so as not to overflow by adding an invalid bit.
[0018]
In the case of variable transfer rate, the definition of this fixed transfer rate is expanded so that when the buffer occupancy reaches the upper limit value, it is defined so that overflow will not occur in principle by stopping reading of the decoder. ing. Such a buffer transition is shown in FIG. Even if the amount of generated code is very small, reading of the decoder is stopped, so there is no need to insert invalid bits as in the case of a fixed transfer rate. Therefore, encoding is performed so that only underflow does not occur.
[0019]
Conventionally, according to the invention of Japanese Patent Laid-Open No. 11-74799, when editing compressed data such as MPEG data recorded on a recording medium, the VBV buffer is always fixed at the editing point in order to maintain the continuity of the MPEG data. There are described methods for performing coding in consideration of continuity, such as controlling the amount of generated code so that the GOP becomes equal, or coding the GOP as a closed GOP.
[0020]
Further, according to the invention of Japanese Patent Laid-Open No. 11-187354, there is no restriction on the encoded data, and the information indicating the data extracted as the editing material in the partial section of the data and the reproduction order thereof. A method is described in which information can be described and video editing can be realized on a single recording medium without changing the recorded data.
[0021]
[Problems to be solved by the invention]
However, in the conventional method described above, when MPEG image data is simply connected, a contradiction occurs in the connection of the VBV buffer, and overflow and underflow occur. In the case of fixed-length coding, the value of VBV is described in units of pictures, and by observing the image bitstream, the start value of VBV at the start point for additional recording can be calculated. It was possible, but it also had to be partially decoded into MPEG compressed data. Further, in the case of variable length coding, the value of VBV is not described in the syntax at all, so that the amount of generated code of each picture must be observed and calculated from the beginning of the compressed data. This required more circuitry and computation time.
[0022]
In the invention of Japanese Patent Laid-Open No. 11-74799, the generated code amount is controlled so that the VBV buffer is always fixed for each GOP so that it can be edited anywhere, the GOP is encoded as a closed GOP, etc. Encoding restrictions considering continuity are imposed, which is a disadvantageous factor in encoding efficiency.
[0023]
In the invention disclosed in Japanese Patent Laid-Open No. 11-187354, playback is displayed as if it had been edited, but the continuity at the editing point is incomplete, and temporary rest such as initialization of the decoder buffer of MPEG data is performed. There was a possibility that the phenomenon occurred.
[0024]
Even when new MPEG image data is additionally recorded from the middle or the end of the already recorded MPEG image data, the present invention does not cause an inconsistency in overflow or underflow in the connection of the VBV buffer during playback. It is an object of the present invention to provide an MPEG image data recording method that enables easy reproduction. Furthermore, the present invention provides MPEG image data that can be used to determine the VBV start value at the start point when additional recording is performed without decoding the already recorded MPEG image data, thereby reducing the circuit scale and the calculation time. It aims to provide a recording method.
[0025]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides the following recording method.
(1) In an MPEG image data recording method for recording MPEG image data, which is image data compressed by the MPEG encoding method,
Information indicating the VBV buffer occupancy value at the end of picture encoding one frame before the I picture in the bit stream of MPEG image data, and the VBV buffer occupancy value at the end of picture encoding one frame before the P picture And information indicating the VBV buffer occupation value at the end of recording,
Generating each address information indicating the VBV buffer occupancy value at which point of the MPEG image data each VBV buffer occupancy value;
Recording the information indicating each VBV buffer occupation value and the address information together with the MPEG image data on a recording medium,
A method for recording MPEG image data.
(2) In an MPEG image data recording method for recording MPEG image data, which is image data compressed by the MPEG encoding method,
The first MPEG image data already recorded includes information on the VBV buffer occupancy value at the end of picture encoding one frame before the I picture in the bit stream of the first MPEG image data, and 1 of the P picture. Information about the VBV buffer occupancy value at the end of picture encoding before the frame, information about the VBV buffer occupancy value at the end of recording, and each VBV buffer occupancy value at which point in time of the first MPEG image data It is recorded with address information indicating whether it is a buffer occupancy value,
When the second MPEG image data is additionally recorded from the end position of the first MPEG image data or the middle position of the first MPEG image data,
Detecting information indicating the VBV buffer occupation value corresponding to a position closest to an additional recording start position of the second MPEG image data in the first MPEG image data based on the address information;
Based on the information indicating the detected VBV buffer occupation value, VBV buffer control is started, MPEG encoding of the second image data is performed to obtain the second MPEG image data,
Recording the second MPEG image data on a recording medium;
A method for recording MPEG image data.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Using the present invention, even when new MPEG image data is additionally recorded from the middle of the already recorded MPEG image data or from the end, there is no inconsistency in overflow or underflow in the connection of the VBV buffer during playback. , Enabling seamless playback. Furthermore, if the present invention is used, the start value of VBV at the start point when additional recording is performed without decoding the already recorded MPEG image data can be known, so that the circuit scale and the calculation time can be reduced.
[0027]
The concept of the present invention will be described with reference to FIG. MPEG image data, which is image data compressed by the MPEG encoding method, is recorded on the recording medium. The MPEG image data is recorded as a bit stream in which a plurality of continuously reproducible data encoded and generated in one recording unit is continuously connected.
[0028]
In addition to the encoded MPEG image data bit stream, the VBV buffer value (occupancy value) at the end of picture encoding one frame before the I picture in the MPEG image data bit stream, and 1 P picture VBV buffer value (occupancy value) at the end of picture encoding before the frame, VBV buffer value (occupancy value) at the end of recording, and the VBV buffer occupancy value at which point in the MPEG image data each VBV buffer value Address information (in this example, a relative address from the beginning of the MPEG image data file) is recorded. A data structure of VBV buffer information including these data is shown in FIG.
[0029]
VBV buffer information has a hierarchical structure. There is an entry point information structure first, followed by a VBV information structure. In the entry point information structure, first, the number of addresses of entry points (EP) is described in 32 bits, and then an EPn (n is a natural number of 1 or more) address is described in 32 bits in order. The EPn address indicates a position where EPn information (n is a natural number of 1 or more) of the VBV information structure is described, and describes a relative address from the top of the VBV buffer information. On the other hand, the VBV information structure is described in order from the EP1 information, and the contents of the EP1 information describe the relative address, the PTM value, and the VBV value in order.
[0030]
As shown in FIG. 2, the relative address in the EPn information of the VBV information structure means the end of picture encoding one frame before the I picture in the bit stream of MPEG image data, and the end of picture encoding one frame before the P picture. This is a relative address from the beginning of the MPEG image data at the time point and at the end of recording. For example, the unit is a byte. When recorded on a disk medium, a sector or the like is used as a relative address.
[0031]
The PTM value in the EPn information of the VBV information structure is a time stamp recorded with a clock of 90 kHz or 27 MHz in the MPEG system standard (multiplexing standard). In the MPEG standard, it is called PTS (Presentation Time Stamp) or DTS (Decoding Time Stamp). Here, the DTS is recorded as time information at the end of picture encoding one frame before the I picture of the bit stream of the MPEG image data, at the end of picture encoding one frame before the P picture, and at the end of recording. . One DTS is recorded in one picture, and an NTSC video signal is recorded at an interval of 3003 clocks per picture with a 90 kHz clock. Therefore, when there is an I picture or a P picture every three pictures as in the present invention, and the first starts from 0, the PTM information is EPn information at intervals of 9009, 18018. Will be described.
[0032]
The VBV value in the EPn information of the VBV information structure is a virtual buffer occupation value of the decoder defined by MPEG. Completion of picture coding one frame before the I picture of the compressed bitstream information as shown in FIG. 3, which can be derived from the amount of generated code for each picture of MPEG image data and the transfer rate value. Each VBV occupancy value is described at the end of picture encoding one frame before the P picture and at the end of recording (at the position of each circle shown in FIG. 3). Alternatively, the VBVdelay value defined by MPEG at each time point is described. This value is a value converted to the time required for the transfer rate at that time to the VBV occupation value. In the present invention, the VBV value may be anything as long as it is information related to the VBV buffer occupation value.
[0033]
In MPEG compression, encoding is basically performed using I or P picture types in units of 3 frames such as IBB and PBB. In MPEG compression, B picture may be predicted from both directions, so in the encoded bit stream order, data linkage is added only at the end of picture encoding one frame before the I picture and P picture of the bit stream. Is not easy. Therefore, the present invention is characterized in that the VBV information is described at the end of picture encoding one frame before the I picture and P picture of the bit stream.
[0034]
Next, the configuration of an embodiment of the recording apparatus according to the present invention is shown in FIG. 4, and the operation of creating VBV buffer information while encoding image data by the MPEG encoding method will be described.
[0035]
When there is no encoded data in the recording medium 31, that is, when encoding is performed for the first time, the data reading unit 32 from the recording medium 31 indicates that no data exists, so that information indicating that there is no data is indicated as VBV buffer information. Transmit to detector 33. Since no data exists in the VBV buffer information detector 33, the initial value set in advance in the parameter setting unit 34, that is, the VBV value is set to, for example, 80% of the maximum value of VBV defined by MPEG. The time stamp information is 0. These initial set values are transmitted to the image encoder 35.
[0036]
The image encoder 35 starts encoding from an initial set value. In the image encoder 35, while encoding, the generated code amount, PTM value, and VBV value at the end of picture encoding one frame before the I picture of the bit stream and one frame before the P picture are Transmit to the VBV buffer information creator 36. At the same time, the encoded data is transmitted to the data writing unit 37. Further, the image encoder 35 transmits the generated code amount, the PTM value, and the VBV value when the user temporarily stops or ends the image compression recording to the VBV buffer information creator 36.
[0037]
The VBV buffer information creator 36 creates VBV buffer information data having the structure shown in FIG. 1 from the generated generated code amount value, PTM value, and VBV value. Alternatively, data necessary for creating the data structure is stored in memory and recorded and held in a predetermined format. The information created by the VBV buffer information creator 36 may be written in bursts simultaneously when encoded data (MPEG image data) is written on the recording medium 31 by the data writing unit 37. The information generated by the VBV buffer information generator 36 is recorded and held in a predetermined format after the encoded data (MPEG image data) has been written, that is, after the user has paused or ended the image compression recording. The written data may be converted into the structure shown in FIG.
[0038]
Next, a new image is added to the encoded data (MPEG image data) already recorded on the recording medium 31 together with the VBV buffer information from a predetermined position in the encoded data (MPEG image data). An operation for recording data will be described.
[0039]
An encoded stream (MPEG image data bit stream) is already recorded on the recording medium 31. Therefore, the data reading unit 32 reads the VBV buffer information from the recording medium 31 and obtains the VBV value, the PTM value, and the relative address. If additional recording is performed from the very end of the encoded stream already recorded, the last value of the existing VBV buffer information (the relative address is the VBV buffer farthest from the beginning of the encoded stream) Information). The position where new MPEG image data is additionally recorded on the recording medium 31 may be a position subsequent to the recording portion of the already recorded MPEG image data, or may be a completely different position.
[0040]
When performing additional writing from the middle of an encoded stream that has already been recorded, the user interface (not shown) specifies from which point of the already recorded image data the additional recording is to be performed. . For example, when the specification method is the positional information of the relative address of the data, the VBV value and the PTM value linked to the data closest to the relative address information in the EPn information of the structure of the VBV buffer information are set. Use. Further, if the designation method is the time from the start time of the data or the time stamp information of the additionally recorded point, the PTM value in the EPn information of the structure of the VBV buffer information is similarly used, When this value is recorded with a 90 kHz clock, the value can be obtained by multiplying the value by 1/90000 second to obtain the time in seconds. The additional recording position (relative address) and VBV value, PTM value can be obtained.
[0041]
These values are input to the parameter setter 34, and the image encoder 35 starts encoding from the set values. (Based on the detected VBV value, VBV buffer control is started and encoding is performed.)
On the other hand, the encoded data search unit 38 searches the already recorded bit stream for a position where additional recording is to be started. In the search, a pointer is set at a position from the head of the bit stream file using the relative address of the data.
[0042]
In the image encoder 35, a VBV buffer information generator is generated each time the generated code amount, PTM value, and VBV value at the end of picture encoding one frame before the I picture and P picture of the bit stream while performing the encoding. 36. At the same time, the encoded data is transmitted to the data writing unit 37. Further, the image encoder 35 transmits the generated code amount, the PTM value, and the VBV value when the user temporarily stops or ends the image compression recording to the VBV buffer information creator 36.
[0043]
The VBV buffer information creator 36 creates VBV buffer information data having the structure shown in FIG. 1 from the generated generated code amount value, PTM value, and VBV value. Alternatively, data necessary for creating the data structure is stored in memory and recorded and held in a predetermined format. The information created by the VBV buffer information creator 36 may be written in bursts simultaneously when encoded data (MPEG image data) is written on the recording medium 31 by the data writing unit 37. The information generated by the VBV buffer information generator 36 is recorded and held in a predetermined format after the encoded data (MPEG image data) has been written, that is, after the user has paused or ended the image compression recording. The written data may be converted into the structure shown in FIG.
[0044]
New MPEG image data is additionally recorded from the point of additional recording in the middle of the already recorded MPEG image data.
[0045]
Note that new MPEG image data that is additionally recorded in the middle part of the already recorded MPEG image data may be recorded so as to be overwritten on the part on which the MPEG image data is already recorded on the recording medium 31. Good. Further, it may be recorded on a part on the recording medium 31 that is completely different from the part on the recording medium 31 on which MPEG image data is already recorded. (In this case, it is necessary to link the additional recording point on the already recorded MPEG image data and the new MPEG image data.)
In the above description, the new MPEG image data to be additionally recorded has been described as being recorded on a recording medium on which MPEG image data has already been recorded. However, together with the MPEG image data read from the recording medium 31, the above method is used. You may record on another recording medium.
[0046]
In the above-described embodiment, the system is described as a single recording apparatus. However, the recording medium may be a database via a network.
[0047]
【The invention's effect】
As described above, if the present invention is used, even when new MPEG image data is additionally recorded from the middle of the already recorded MPEG image data or from the end, contradiction of overflow or underflow in the connection of the VBV buffer during playback. This makes it possible to perform seamless and high quality playback. Furthermore, if the present invention is used, the start value of the VBV buffer occupancy value at the starting point in the case of additional recording without decoding the already recorded MPEG image data can be known, and the circuit scale can be reduced and additional recording can be performed. Processing time can be shortened.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of a VBV buffer information structure according to the present invention.
FIG. 2 is a diagram showing the relationship between MPEG image data and relative addresses in the present invention.
FIG. 3 is an explanatory diagram illustrating a VBV value.
FIG. 4 is a block diagram showing an embodiment of an MPEG image data recording apparatus according to the present invention.
FIG. 5 is a diagram illustrating an example of a conventional MPEG encoder.
FIG. 6 is a diagram illustrating an example of a conventional MPEG decoder.
FIG. 7 is a diagram for explaining the concept of a VBV buffer in MPEG.
[Explanation of symbols]
31 Recording medium 32 Data reading unit 33 VBV buffer information detector 34 Parameter setting unit 35 Image encoder 36 VBV buffer information creation unit 37 Data writing unit 38 Encoded data search unit

Claims (2)

In an MPEG image data recording method for recording MPEG image data which is image data compressed by the MPEG encoding method,
Information indicating the VBV buffer occupancy value at the end of picture encoding one frame before the I picture in the bit stream of MPEG image data, and the VBV buffer occupancy value at the end of picture encoding one frame before the P picture And information indicating the VBV buffer occupation value at the end of recording,
Generating each address information indicating the VBV buffer occupancy value at which point of the MPEG image data each VBV buffer occupancy value;
Recording the information indicating each VBV buffer occupation value and the address information together with the MPEG image data on a recording medium,
A method for recording MPEG image data. In an MPEG image data recording method for recording MPEG image data which is image data compressed by the MPEG encoding method,
The first MPEG image data already recorded includes information on the VBV buffer occupancy value at the end of picture encoding one frame before the I picture in the bit stream of the first MPEG image data, and 1 of the P picture. Information about the VBV buffer occupancy value at the end of picture encoding before the frame, information about the VBV buffer occupancy value at the end of recording, and each VBV buffer occupancy value at which point in time of the first MPEG image data It is recorded with address information indicating whether it is a buffer occupancy value,
When the second MPEG image data is additionally recorded from the end position of the first MPEG image data or the middle position of the first MPEG image data,
Detecting information indicating the VBV buffer occupation value corresponding to a position closest to an additional recording start position of the second MPEG image data in the first MPEG image data based on the address information;
Based on the information indicating the detected VBV buffer occupation value, VBV buffer control is started, MPEG encoding of the second image data is performed to obtain the second MPEG image data,
Recording the second MPEG image data on a recording medium;
A method for recording MPEG image data.

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