JPH06326998A - Moving picture encoder - Google Patents

Abstract

PURPOSE:To smoothly and simply reproduce moving picture encoded data on the way or at a high speed by inserting a value indicating the difference from the actual start position to a start position as the target of GOP and reading out the start position as the target of GOP. CONSTITUTION:An encoder 11 encodes input moving picture data and outputs it to a transmission buffer 12 being a buffer memory. A code quantity counter 13 counts the code quantity generated in the encoder 11 and supplies it to a controller 14. Encoded data written in the transmission buffer 12 and the data of contents supplied to the controller 4 are transferred to a storage medium 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture coding apparatus for compressing digital moving picture data.

[0002]

2. Description of the Related Art Various moving image coding systems for compressing digital moving image data have been proposed in the past. Among them, the system proposed as an international standard is "International Standard for Multimedia Coding" ( Hiroshi Yasuda and Maruzen).

In the above-mentioned conventional moving picture coding system, each image forming the moving picture data is classified as follows according to the coding method. That is, an I picture (Intra-coded picture) that performs only intra-frame coding, and a P picture (Predictive-coded) that performs inter-frame predictive coding using an image that is temporally preceding as a prediction image. picture: forward predictive coded image),
Then, a B picture (Bidirectionally predictive) in which interframe predictive coding is performed by using both an image that is temporally preceding and an image that is temporally posterior as a predictive image.
-coded picture: bidirectional predictive coded image).

A picture group composed of one or a plurality of I pictures and zero or more P or B pictures is called GOP (Group Of Picture), and the whole moving picture data (called a video sequence). Is composed of one or more GOPs.

FIG. 3 shows an outline of an encoded bitstream syntax having the above structure. FIG. 3A shows the video sequence layer. In FIG. 3A, SSC (Sequence Start C
ode) 1 is a fixed synchronization code that represents the beginning of a video sequence. The sequence header 2 contains the image size,
It includes parameters such as image rate and bit rate. The picture group GOP3 constitutes the entire moving image data, and the SEC (Sequence End Code) 4 is a fixed synchronization code indicating the end of the video sequence.

FIG. 3B shows the layer of GOP3 in FIG. 3A, and GSC (Group Start Code) 5
Is a fixed synchronization code indicating the beginning of GOP3.
The GOP header 6 includes parameters such as time code. Moreover, PICT7 represents the picture which comprises moving image data.

FIG. 3 (c) shows the picture layer of FIG. 3 (b), and PSC (Pictrue Start Code) 8 is shown.
Is a fixed sync code that represents the beginning of a picture.
The picture header 9 includes parameters such as the type of I picture, P picture, B picture, etc. described above. S
The LICE 10 is one layer below the picture.

The above-mentioned synchronization codes are all byte-aligned. Regarding the amount of generated code,
Capacity B read at bit rate R [bit / s]
Image rate PR in virtual buffer of [bit]
It is stipulated that the buffer occupancy Bn [bit] (n is an image number) immediately after writing one image of moving picture data of [picture / s] satisfies the condition of 0 <Bn <BX. (However, X = R / PR). This is shown in the graph of the generated code amount as shown in FIG.

Consider a case in which coded data having the above-described bit stream syntax is stored in a storage medium and is played back from the middle or high-speed playback is performed.

When reproducing from the middle, a GOP3 having a desired time code is found and the data after GOP3 is decoded. Further, in the case of high-speed reproduction, the cue of only the I picture included in at least one GOP is speeded up, and only that picture is decoded and displayed. In any case, from the encoded data recorded on the storage medium,
It is necessary to detect the head of GOP3, that is, GSC5.

[0011]

[Problems to be Solved by the Invention] However, GSC
Although the position of 5 is byte-aligned, it is variable-length coded, so accurate position prediction cannot be performed unless decoding is actually performed. Therefore, it is necessary to detect GSC while reading data in byte units within the range of the generated code amount due to the buffer capacity described above.
There is a problem that the detection takes time and the time required for the GSC detection may vary widely.

Further, in the above-mentioned regulation of the generated code amount, since the code amount of the I picture is generally larger than that of the P picture and B picture, the generated code amount before and after the I picture is underflow and overflow. It tends to approach the limit.

The present invention has been made in view of the above points, and makes it possible to easily and smoothly perform midway playback or high-speed playback by shortening the time required for GSC detection and keeping it substantially constant. In addition, it is an object of the present invention to provide a moving picture coding apparatus that is capable of achieving the above, and is unlikely to cause underflow and overflow of the coded data buffer.

[0014]

That is, according to the present invention, at least one frame in which an input image signal having a frame rate n [frame / s] is intra-coded, and 0
Dividing into a frame group consisting of m [frames] composed of one or more frames for inter-frame predictive coding, variable length coding is performed as a succession of this frame group, and the generated code amount per unit time is set to a target value R In a moving picture coding apparatus that approaches [bit / s], a counting unit that counts the actual generated code amount, and a generated code amount storage unit that stores the actual generated code amount counted by this counting unit, Target generated code amount (m / n) × R of the above frame group of encoded output data
It is characterized by comprising control means for controlling so as to insert a value indicating a difference from the actual start position of the data of the frame group at every [bit] position.

[0015]

In the moving picture coding apparatus according to the present invention, the GOP
A value indicating the difference from the actual start position is inserted into the target start position of. With this, the beginning of GOP,
In other words, in order to detect GSC, it is only necessary to read the target start position of GOP.
The time required to detect C is short and almost constant.

Further, the reading of the buffer memory for transmitting the encoded data output to the storage medium is normally performed intermittently, but the frequency is increased when the encoded data of the I picture is written. As a result, even if the actual generated code amount varies depending on the input image,
Underflow and overflow are less likely to occur.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the moving picture coding apparatus of the present invention.

In the figure, the input moving image data is encoded by the encoder 11 and output to the transmission buffer 12 which is a buffer memory. The code amount counter 13 counts the generated code amount in the encoder 11, and supplies the generated code amount to the controller 14. Send buffer 12
The coded data written in and the data such as the header that the controller 4 inserts into the bitstream are transferred to the storage medium 15.

In such a structure, the encoder 11
Divides the input moving image data at the frame rate n [frame / s] into GOPs composed of images at m [frame].
Then, intraframe coding is performed on at least one image per GOP, and interframe predictive coding is performed on the remaining images. The data encoded by the encoder 11 is written in the transmission buffer 12.

On the other hand, the generated code amount in the encoder 11 at this time is counted by the code amount counter 13. The controller 14 reads the generated code amount and controls the encoder 11 so that the average generated code amount per unit time approaches the target value R [bit / s]. At the same time, the coded data written in the transmission buffer 12 is transferred to the storage medium 15 while inserting the synchronization code indicating the beginning of the sequence, GOP, picture, etc., and the header of each layer, etc. into an appropriate position. Furthermore, at this time, since the generated code amount fluctuates depending on the input image at the position of the target code amount (m / n) × R [bit] of the GOP, the fluctuation amount of the actual GOP start position fluctuates. Insert a value that represents.

The controller 14 transfers the encoded data having the above contents to the storage medium 15, and the data rate thereof is the target generated code amount R per unit time.
It is larger than [bit / s] and is performed intermittently. The frequency is high when the encoder 11 performs intra-frame coding and is low when performing inter-frame predictive coding. That is, it is increased when the encoded data of the I picture is written.

FIG. 2 is a graph showing the relationship between the generated code amount and the read code amount at this time. As is clear from the figure, even with the same buffer size, the generated code amount has a margin for each limit of underflow and overflow as compared with FIG. Therefore, underflow and overflow are less likely to occur even if the actual generated code amount varies depending on the input image.

As described above, in the moving picture coding apparatus according to the embodiment, GO in the coded moving picture data is used.
Since a value indicating the actual start position of the GOP is inserted at the position of the target code amount of P, the start of the GOP can be accessed easily and quickly by reading this value. As a result, it is possible to smoothly and easily perform high-speed reproduction in which a moving image is reproduced halfway or only intra-frame coded data is reproduced one after another.

Further, since the reading speed of the transmission buffer becomes high at the time of intra-frame coding with a large amount of generated code,
The possibility of underflow and overflow of the buffer can be reduced as compared with the case of reading at a constant speed with the same buffer capacity.

[0025]

As described above, according to the present invention, it is possible to smoothly and easily perform reproduction from the middle or high-speed reproduction of the output moving image coded data, and also to prevent underflow of the transmission buffer, It is possible to realize a moving picture coding device in which overflow does not easily occur.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a moving picture coding apparatus according to the present invention.

FIG. 2 is a graph showing the relationship between the generated code amount and the read code amount according to the embodiment of the present invention.

3A and 3B are schematic diagrams of encoded bitstream syntax, where FIG. 3A is a diagram showing a video sequence layer, FIG. 3B is a diagram showing a GOP layer, and FIG.
(C) is a figure shown about a picture layer.

FIG. 4 is a graph showing a relationship between a generated code amount and a read code amount of a conventional moving image coding apparatus.

[Explanation of symbols]

1 ... SSC (Sequence Start Code), 2 ... Sequence header, 3 ... GOP (Group Of Picture), 4 ... SEC
(Sequence End Code), 5 ... GSC (Group Start Cod)
e), 6 ... GOP header, 7 ... PICT (picture),
8 ... PSC (Pictrue Start Code), 9 ... Picture header, 10 ... SLICE, 11 ... Encoder, 12 ... Transmission buffer, 13 ... Code amount counter, 14 ... Controller,
15 ... Storage media.

Claims (1)

[Claims] 1. An input image signal having a frame rate of n [frames / s] is composed of at least one frame for intra-frame coding and zero or more frames for inter-frame predictive coding. Frames], variable length coding is performed as a sequence of these frame groups, and the generated code amount per unit time is set to a target value R [bi
t / s] in a moving picture coding apparatus, counting means for counting the actual generated code amount, generated code amount storage means for storing the actual generated code amount counted by the counting means, A control is performed so that a value indicating the difference from the actual start position of the data of the frame group is inserted into positions of the target generated code amount (m / n) × R [bit] of the frame output group of the encoded output data. A moving picture coding apparatus, comprising: a control means.