JP2002112183A - Mpeg image data recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain seamless reproduction, without causing contradiction in overflow and underflow at connection of a VBV buffer in the case of reproduc tion, even when new MPEG image data is appended to the midway or at the end of MPEG image data having already been recorded. SOLUTION: In addition to a bit stream of the MPEG image data, a VBV buffer value at the time of end of picture coding of one preceding frame to an I picture of the bit stream, a VBV buffer value at a point of time of end of picture coding of one preceding frame to a P picture, a VBV buffer value at a point of time of recording end, and address information denoting, to which point of time of the MPEG image data each VBV buffer value above corresponds are recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording MPEG image data, which is image data compressed by the MPEG encoding method, on a recording medium. It is another object of the present invention to provide an MPEG image data recording method which enables seamless reproduction when additionally recorded MPEG image data is reproduced.

[0002]

2. Description of the Related Art First, a conventional MPEG will be briefly described. For MPEG, see ISO-IEC11172-2, ITU-T H.
262 / ISO-IEC13818-2 provides a detailed explanation, so only an outline is given here. MPEG in 1988, ISO / IE
C Name of the organization (Moving Pictures) that considers moving picture coding standards established in JTC1 / SC2 (International Organization for Standardization / Technical Committee of the International Electrotechnical Commission / Technical Committee 2, current SC29)
Expert Group). MPEG1 (MPEG phase 1)
Is a standard for storage media of about 1.5 Mbps, JPEG for the purpose of still image encoding, and H.264 for the purpose of moving image compression for low transfer rates of ISDN video conferences and videophones.
It inherits the basic technology of 261 (CCITT SGXV, standardized by the current ITU-T SG15) and introduces new technology for storage media. These are August 1993, ISO / IEC 11172
It is established as.

[0003] MPEG is created by combining several techniques. FIG. 5 shows a conventional MPEG encoder, which will be briefly described below. For the input image, a difference between the image decoded by the motion compensation predictor 1 and the input image is obtained by a differentiator 2 to reduce a time redundant part.

[0004] The direction of prediction is three from the past and the future.
Mode exists. These are 16 pixels x 16 pixels MB
(Macro block) can be switched and used. The prediction direction is determined by the picture type given to the input image. A mode of encoding by prediction from the past,
Mode 2 in which the MB is coded independently without prediction
There are two modes for P-pictures. Also,
The B picture has four modes for prediction from the future, prediction from the past, prediction from both, and independent encoding. And it is I to encode all MBs independently.
It is a picture.

In the motion compensation, a motion vector is detected with half-pel accuracy by performing pattern matching for each MB, and is predicted after shifting by the amount of motion. The motion vector has a horizontal direction and a vertical direction, and is transmitted as MB additional information together with an MC (Motion Compensation) mode indicating where to predict the motion vector.

[0006] A GOP (Group Of Picture) refers to a GOP (Group Of Picture) from an I picture to a picture preceding the next I picture. In general, about 15 pictures are used as one GOP.

[0007] The DCT unit 3 performs orthogonal transformation on the difference image. The DCT (Discrete Cosine Transform) is an orthogonal transform that discretely transforms an integral transform using 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. Generally, since a video signal has many low-frequency components and few high-frequency components, when DCT is performed, coefficients concentrate on low frequencies.

The quantized image data (DCT coefficients) are quantized by the quantizer 4. The quantization is performed by quantizing the DCT coefficients by multiplying a value obtained by weighting the 8x8 two-dimensional frequency called a quantization matrix by visual characteristics and a value called a quantization scale that multiplies the whole by a scalar as a quantization value. Calculate by value. When inverse quantization is performed by the MPEG decoder (decoder), a value close to the original DCT coefficient is obtained by multiplying by the quantization value.

[0009] The quantized data is subjected to variable length coding by a VLC unit 5. A direct current (DC) component of the quantized value is a DPCM (differential pul
Use se code modulation). For the AC component, Huffman coding is performed by performing a zigzag scan from the low band to the high band, assigning a run length of zero and an effective coefficient value to one event, and assigning a code with a short code length from the one with the highest occurrence probability. Done.

The variable-length coded data is stored in a temporary buffer 6 and output as coded data at a predetermined transfer rate. The generated code amount of the output data for each macro block is transmitted to the code amount controller 21.
The code amount is controlled by feeding back the error code amount between the target code amount and the generated code amount to the quantizer 4 and adjusting the quantization scale.

The quantized image data is inversely quantized by an inverse quantizer 7, inverse DCT by an inverse DCT unit 8, temporarily stored in an image memory 10 via an adder 9, and then subjected to motion compensation. In the predictor 1, the difference image is used as a reference decoded image for calculating a difference image.

FIG. 6 shows an MPEG decoder (decoder) for decoding the coded data thus MPEG-coded.

Incoming encoded data (stream) is buffered in a buffer 11, and data from the buffer 11 is input to a VLD unit 12. The VLD unit 12 performs variable length decoding to obtain a direct current (DC) component and an alternating current (AC) component. Alternating current (AC) component data from low to high
They are arranged in an 8 × 8 matrix in the order of gzag scan.
This data is input to the inverse quantizer 13 and inversely quantized by the quantization matrix. Inverse quantized data is inverse
The data is input to the DCT unit 14, 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.

In the case of video, the coded bit stream has a variable length code amount for each picture.
This is because MPEG uses information transforms such as DCT, quantization and Huffman coding.At the same time, it is necessary to adaptively change the amount of code allocated to each picture in order to improve image quality. This is because the entropy of the encoded image itself greatly changes, for example, in some cases, the input image is encoded as it is, and in some cases, the difference image, which is the difference between the predicted images, is encoded.

In this case, in most cases, the code amount is controlled while allocating to the entropy ratio of the image and keeping the buffer limit. The buffer manager monitors the relationship between the generated code amount and the coding rate, and sets a target code amount so as to be contained in a predetermined buffer. This value is fed back to the variable-length encoder and enters the code amount controller, where the quantized value set in the quantizer is increased to suppress the generated code amount, or the quantized value is reduced to reduce the generated code amount. Or make it smaller.

When such variable length data is encoded at a fixed transfer rate (encoding rate), if the maximum buffer amount of the decoder is set as an upper limit, data is input at a constant speed and only a predetermined value is input. Because it has accumulated, MPEG is used to decode the video instantaneously at a predetermined time (1 / 29.97 sec for NTSC video signals), and to encode the buffer so that neither overflow nor underflow occurs. Stipulated in If this rule (VBV buffer rule) is adhered to, the rate in the VBV buffer is locally changed, but if the observation time is long, the transfer rate becomes fixed. In MPEG, this is a fixed rate. Has defined.

In the case of a fixed transfer rate, if the generated code amount is small, the buffer occupancy is stuck at the upper limit. In this case, the code amount must be increased by adding an invalid bit so as not to overflow.

In the case of the variable transfer rate, the definition of the fixed transfer rate is extended, and when the buffer occupancy reaches the upper limit, the reading of the decoder is stopped so that overflow does not occur in principle. Is defined in FIG. 7 shows such a buffer transition. Even if the generated code amount is very small, the reading of the decoder is stopped, so that there is no need to insert an invalid bit as in the case of the fixed transfer rate. Therefore, encoding is performed so that only underflow does not occur.

Further, according to the invention disclosed in Japanese Patent Application Laid-Open No. H11-74799, when editing compressed data such as MPEG data recorded on a recording medium, a VBV buffer is used at the editing point to maintain the continuity of the MPEG data. There is described a method of performing encoding in consideration of continuity, such as controlling the generated code amount so that is always fixed, encoding the GOP as a closed GOP, and the like.

Further, according to the invention of Japanese Patent Application Laid-Open No. 11-187354, the information indicating the data extracted as the editing material in the partial section of the encoded data without any restrictions on the encoded data and the information A method is described in which information about the reproduction order is described, and video editing can be realized on a single recording medium without changing recorded data.

[0021]

However, in the above-mentioned conventional method, when MPEG image data is simply connected, inconsistency occurs in the connection of the VBV buffer, and overflow or underflow occurs. Also, in the case of fixed-length coding, the value of VBV is described in picture units, and by observing the image bit stream, the start value of VBV at the start point for additional recording can be calculated. Yes, but it also had to decode some to MPEG compressed data. Furthermore, in the case of variable length coding, VBV
Is not described in the syntax at all, so it was necessary to observe and calculate the generated code amount of each picture from the beginning of the compressed data. This required more circuitry and computation time.

In the invention of Japanese Patent Laid-Open No. 11-74799, a VBV
Controlling the amount of generated code so that the buffer is always fixed, or coding the GOP as a closed GOP, imposes coding restrictions that take into account continuity, which is a disadvantageous factor in terms of coding efficiency. I was

Further, in the invention of Japanese Patent Application Laid-Open No. H11-187354, reproduction and display are performed as if edited, but the continuity at the editing point is incomplete, and temporary processing such as initialization of a decoder buffer for MPEG data is performed. Static phenomena could occur.

According to the present invention, even when new MPEG image data is additionally recorded from the middle or from the end of the already recorded MPEG image data, inconsistency of overflow or underflow occurs in the connection of the VBV buffer during reproduction. It is intended to provide an MPEG image data recording method that enables seamless reproduction without any problem. Furthermore, the present invention provides a method of determining the start value of VBV at the start point when additional recording is performed without decoding already recorded MPEG image data, thereby enabling MPEG image data to be reduced in circuit size and calculation time. It aims to provide a recording method.

[0025]

Accordingly, in order to solve the above-mentioned problems, the present invention provides the following recording method. (1) Image data compressed by the MPEG encoding method
In the MPEG image data recording method for recording MPEG image data, the MPEG image data bit stream
The information indicating the VBV buffer occupancy value at the end of picture coding one frame before the I picture, the information indicating the VBV buffer occupancy value at the end of picture coding one frame before the P picture, Information indicating the VBV buffer occupancy value of the MPEG image data is generated, and address information indicating at which point in time the VBV buffer occupancy value of the MPEG image data is the VBV buffer occupancy value. Recording the MPEG information and the address information together with the MPEG image data on a recording medium. (2) Image data compressed by the MPEG encoding method
In the MPEG image data recording method for recording MPEG image data, the first MPEG image data that has already been recorded is an I-bit in the bit stream of the first MPEG image data.
Information about the VBV buffer occupancy value at the end of picture encoding one frame before the picture, information about the VBV buffer occupancy value at the end of picture encoding one frame before the P picture, and the VBV buffer at the end of recording Occupancy value and address information indicating at which point in time the VBV buffer occupancy value of the first MPEG image data is the VBV buffer occupancy value, wherein the first MPEG When additionally recording the second MPEG image data from the end position of the image data or the middle position of the first MPEG image data, additional recording of the second MPEG image data in the first MPEG image data is started. The VBV corresponding to the position closest to the position
The information indicating the buffer occupancy value is detected based on the address information, the VBV buffer control is started based on the detected information indicating the VBV buffer occupancy value, and the MPEG encoding of the second image data is performed. MPEG image data,
A method for recording MPEG image data, comprising recording the second MPEG image data on a recording medium.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, even when new MPEG image data is additionally recorded from the middle or from the end of already recorded MPEG image data, it is possible to perform reproduction at the time of reproduction.
Seamless playback is possible without causing inconsistency of overflow or underflow in the connection of the VBV buffer. Further, according to the present invention, the already recorded MP
The start value of VBV at the start point when additional recording is performed without decoding the EG image data can be known, so that the circuit size can be reduced and the calculation time can be reduced.

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 are continuously connected.

Apart from these coded MPEG image data bit streams, the VBV buffer value (occupation value) at the end of picture coding one frame before the I picture in the MPEG image data bit stream, and P The VBV buffer value (occupancy value) at the end of picture encoding one frame before the picture, the VBV buffer value (occupancy value) at the end of recording, and the VBV buffer value at each point in the MPEG image data at each of the VBV buffer values Address information (in this example, a relative address from the beginning of the file of the MPEG image data) indicating whether the value is a buffer occupancy value is recorded.
FIG. 1 shows a data structure of VBV buffer information including these data.

The VBV buffer information has a hierarchical structure. First there is an entry point information structure, followed by a VBV information structure. In the entry point information structure, the number of entry point (EP) addresses is first described in 32 bits, and the EPn (n is a natural number of 1 or more) address is described in 32 bits in order. EPn address is EPn information of the VBV information structure (n is a natural number of 1 or more)
Is described, and a relative address from the head of this VBV buffer information is described. On the other hand, the VBV information structure is described in order from the EP1 information, and the content of the EP1 information describes a relative address, a PTM value, and a VBV value in order.

The relative address in the EPn information of the VBV information structure is, as shown in FIG. 2, the end point of the encoding of the picture one frame before the I picture and the picture one frame before the P picture in the bit stream of the MPEG image data. At the end of encoding and at the end of recording,
This is a relative address from the beginning of the MPEG image data. For example, the unit is a byte. When recorded on a disk medium, a sector or the like is used as a relative address.

The PTM value in the EPn information of the VBV information structure refers to a value of 90 in the MPEG system standard (multiplexing standard).
This is a time stamp recorded with a clock of kHz or 27 MHz. In the MPEG standard, PTS (Presentation Ti
me Stamp) and DTS (Decoding Time Stamp). Here, I of the bit stream of the MPEG image data
The DTS is recorded as time information at the end of picture encoding one frame before the picture, 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 N
In the case of a TSC video signal, it is recorded at an interval of 3003 clocks per picture at 90 KHz clocks.
Therefore, in the case where an I picture or a P picture exists for every three pictures as in the present invention and the beginning starts from 0, the PTM information is provided at intervals of 9009, 18018. Will be described.

The VBV value in the EPn information of the VBV information structure is a virtual buffer occupancy value of a decoder specified by MPEG. It can be derived by calculation from the generated code amount for each picture of MPEG image data and the value of the transfer rate.
At the end of picture coding one frame before the I picture of the compressed bit stream information,
Each VBV occupancy value is described at the time of the end of the picture encoding one frame before the P picture and at the end of the recording (at the position of each O mark shown in FIG. 3). Alternatively, the VBVdelay value specified by the MPEG at each time is described. This value is a value converted to a time that indicates how long it takes at the transfer rate at that time up to the VBV occupation value. In the present invention, the VBV value may be any information as long as it is information on the VBV buffer occupancy value.

In MPEG compression, encoding is basically performed using an I or P picture type in units of three frames, such as IBB and PBB. In MPEG compression, a B picture may be predicted from both directions, so in the order of the encoded bit stream, data connection is added only at the end of the picture encoding of the I-picture of the bit stream and one frame before the P picture. Is not easy. Therefore, the present invention is characterized in that VBV information is described at the end of picture coding one frame before the I picture and P picture of the bit stream.

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.

When there is no encoded data on the recording medium 31, that is, when encoding is performed for the first time, the data reading unit 32 from the recording medium 31 does not have any data. This is transmitted to the VBV buffer information 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, for example, a value of 80% of the maximum value of VBV specified by MPEG, and the PTM Time stamp information is set to 0. These initial setting values are transmitted to the image encoder 35.

In the image encoder 35, encoding is started from an initial set value. The image encoder 35 encodes the generated code amount, the PTM value, and the VBV value at the end of the picture encoding one frame before the I picture and one frame before the P picture of the bit stream each time while performing the encoding. VB
It is transmitted to the V buffer information generator 36. At the same time, the encoded data is transmitted to the data writing unit 37. Further, the image encoder 35 outputs the generated code amount and the PTM when the user temporarily stops or ends the image compression recording.
The value and the VBV value are transmitted to the VBV buffer information generator 36.

The VBV buffer information generator 36 converts the generated code amount value, the PTM value and the VBV value into the structure shown in FIG.
Create VBV buffer information data. Alternatively, data necessary for creating the data structure is stored in a memory and recorded and held in a predetermined format. The information created by the VBV buffer information creating unit 36 may be written in a burst at the same time that the encoded data (MPEG image data) is written to the recording medium 31 by the data writing unit 37. The information created by the VBV buffer information creating unit 36 is recorded and held in a predetermined format when the encoded data (MPEG image data) has been written, that is, after the user has temporarily stopped or ended the image compression recording. The written data may be converted into the structure of FIG. 1 and written by the data writing unit 37.

Next, the encoded data (MPEG image data) already recorded together with the VBV buffer information on the recording medium 31 is added from a predetermined position in the encoded data (MPEG image data). An operation for recording new image data will be described.

An encoded stream (a bit stream of MPEG image data) 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 a VBV value, a PTM value, and a relative address. When additional recording is performed from the end of the already recorded encoded stream, the last value of the existing VBV buffer information (the VBV buffer whose relative address is the furthest from the beginning of the encoded stream) information)
See On the recording medium 31, the position where the new MPEG image data is additionally recorded depends on the already recorded MP.
The position may be a position following the recording portion of the EG image data, or may be a completely different position.

When additional writing is to be performed from the middle of an already recorded coded stream, a user interface (not shown) is used to specify a point in the already recorded image data from which point to additionally record. do that for me. For example, when the designation method is the position 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 calculated. Used. Also,
If the designation method is the time from the start time of the data or the time stamp information of the point to be additionally recorded, similarly, the PTM in the EPn information of the VBV buffer information structure
If this value is recorded with a clock of 90 KHz using the value, the time can be obtained by multiplying that value by a value of 1 / 90,000 second, and the additional recording position (relative address) in the middle can be obtained. ), VBV value and PTM value can be obtained.

These values are input to the parameter setting unit 34, and the image coding unit 35 starts coding from the set values. (VBV buffer control is started based on the detected VBV value and coding is performed.) On the other hand, the coded data searcher 38 searches the bit stream that has already been recorded for the position at which additional recording is to start. I do. The search uses a relative address of data to set a pointer to a position from the head of the bit stream file.

The image encoder 35 encodes the I-picture and the P-picture of the bit stream while encoding.
The generated code amount, the PTM value, and the VBV value at the time of the end of the picture encoding before the frame are always updated by the VBV buffer information generator 36.
Send to 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 generator 36.

The VBV buffer information creator 36 converts the generated code amount value, the PTM value and the VBV value into the structure shown in FIG.
Create VBV buffer information data. Alternatively, data necessary for creating the data structure is stored in a memory and recorded and held in a predetermined format. The information created by the VBV buffer information creating unit 36 may be written in a burst at the same time that the encoded data (MPEG image data) is written to the recording medium 31 by the data writing unit 37. The information created by the VBV buffer information creating unit 36 is recorded and held in a predetermined format when the encoded data (MPEG image data) has been written, that is, after the user has temporarily stopped or ended the image compression recording. The written data may be converted into the structure of FIG. 1 and written by the data writing unit 37.

[0044] New MPEG image data is additionally recorded from the point of additional recording in the middle of the already recorded MPEG image data.

The new MPEG image data additionally recorded in the middle of the already recorded MPEG image data is as follows:
The recording may be performed so as to overwrite the portion of the recording medium 31 on which the MPEG image data has already been recorded. Further, the image data may be recorded on a part on the recording medium 31 completely different from the part on the recording medium 31 on which the 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 with the new MPEG image data.) In the above description, the newly recorded new MPEG image data is the MPEG image data Although described as being recorded on the recording medium on which data is recorded, it may be recorded on another recording medium by the above-described method together with the MPEG image data read from the recording medium 31.

In the above embodiment, the system is described as a single recording apparatus. However, the recording medium may be a database via a network.

[0047]

As described above, according to the present invention, even if new MPEG image data is additionally recorded from the middle of the already recorded MPEG image data or from the end, overflow occurs at the connection of the VBV buffer during reproduction. This enables seamless and high-quality reproduction without causing inconsistency in image and underflow. Furthermore, according to the present invention, the start value of the VBV buffer occupancy value at the start point when additional recording is performed without decoding already recorded MPEG image data can be known, so that the circuit scale can be reduced and additional recording can be performed. Processing time can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a VBV buffer information structure according to the present invention.

FIG. 2 is a diagram illustrating a relationship between MPEG image data and relative addresses according to 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 device 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.

[Description of Signs] 31 Recording Medium 32 Data Reading Unit 33 VBV Buffer Information Detector 34 Parameter Setting Unit 35 Image Encoder 36 VBV Buffer Information Creating Unit 37 Data Writing Unit 38 Encoded Data Search Unit

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Claims (2)

[Claims] 1. An MPEG image data recording method for recording MPEG image data, which is image data compressed by an MPEG encoding method, comprising: a point at which picture encoding ends one frame before an I picture in a bit stream of the MPEG image data. At
Generating information indicating the VBV buffer occupancy value, information indicating the VBV buffer occupancy value at the end of the picture encoding one frame before the P picture, and information indicating the VBV buffer occupancy value at the end of the recording; Generates address information indicating when each VBV buffer occupancy value is the VBV buffer occupancy value of the MPEG image data, and records the information indicating each VBV buffer occupancy value and the address information together with the MPEG image data. Recording on media,
A method for recording MPEG image data, comprising: 2. An MPEG image data recording method for recording MPEG image data which is image data compressed by an MPEG encoding method, wherein the first MPEG image data already recorded is the first MPEG image data.
VB at the end of picture coding one frame before the I picture in the MPEG image data bit stream
The information relating to the V buffer occupancy value, the information relating to the VBV buffer occupancy value at the end of picture coding one frame before the P picture, the information relating to the VBV buffer occupancy value at the end of recording, and the respective VBV buffer occupancy values are: The first MPEG image data is recorded together with address information indicating at what point in time the VBV buffer occupancy value is, and the end position of the first MPEG image data, or the first MPEG image data,
When additionally recording the second MPEG image data from the middle position of the MPEG image data, the first MPEG image data corresponds to the position closest to the additional recording start position of the second MPEG image data. The information indicating the VBV buffer occupancy value is detected based on the address information, and the VBV buffer occupancy value is detected based on the detected information indicating the VBV buffer occupancy value.
Starting buffer control, performing MPEG coding of second image data to obtain the second MPEG image data, and recording the second MPEG image data on a recording medium. Recording method.