JP2758929B2 - Video coding transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a video signal encoded by an inter-frame prediction method, which is used for a high-speed packet network or an asynchronous transfer mode (ATM)
The present invention relates to a video coding transmission system for transmitting data using a network.

[Conventional technology]

Generally, in high-efficiency video coding, an inter-frame prediction method is used to achieve a high compression rate. In this inter-frame prediction method, it is impossible to correctly decode encoded information unless the frame memories of the encoder and the decoder have the same contents. Therefore, it is necessary to compensate for errors in the frame memories of the encoder and the decoder. Conventionally, the following two types of refresh methods have been used as this compensation method.

When the demand refresh decoder detects an error in the frame memory, it requests the encoder to compensate. The encoder responds to this request by:
The next frame to be transmitted is encoded without performing inter-frame prediction. The decoder refreshes the frame memory with the encoded frame memory without performing inter-frame prediction.

FIG. 4 is a diagram showing one frame divided into n blocks. Hereinafter, the periodic refresh will be described with reference to FIG.

When encoding one frame, the encoder encodes one of the n divided blocks without performing inter-frame prediction.

Also, by moving the positions of the blocks to be coded by rotation, for example, in ascending numerical order without performing inter-frame prediction, refreshing of all blocks is completed during transmission of n frames, and refreshing of the entire frame memory is completed. Done.

On the other hand, in the case of an encoding method using discrete cosine transform, which is one of the high-efficiency encoding techniques, an error occurs in each frame memory of the encoder and the decoder due to a calculation error.

Although this error has a smaller absolute value than an error of the frame memory caused by packet discard or transmission path error, it has a property that it frequently occurs. That is, an error in the frame memory due to a calculation error does not immediately lead to image quality degradation. However, when demand refresh is applied to compensate for the error, the demand refresh is performed frequently, and the amount of information increases, resulting in a decrease in efficiency. is expected.

As described above, when an error occurs in each frame memory of the encoder and the decoder due to the calculation error, the periodic refresh is suitable as a refresh method of the frame memory.

[Problems to be solved by the invention]

By the way, when such a video coded transmission system is used in a high-speed packet network, compensation for frame memory errors caused by packet discarding is not possible because periodic refresh requires a long time for refreshing. Are superimposed, and the image quality deteriorates.

When demand refresh is also used, the time required for compensation is short, but the amount of information increases because one frame is encoded without using inter-frame prediction. Accordingly, if packet refresh is caused by network congestion and demand refresh is used to compensate for the error, there is a risk that network congestion will be worsened.

The present invention has been made to solve such a problem, and it is possible to quickly compensate for an error of each frame memory of an encoder and a decoder caused by packet discarding while suppressing an increase in information amount. An object of the present invention is to provide a video coding transmission system.

[Means for Solving the Problems] FIG. 1 is a block diagram showing the principle of the video encoding transmission system of the present invention.

In the figure, each frame memory of the encoder and the decoder is divided into a plurality of blocks between the encoder and the decoder which encode the video signal by the inter-frame prediction method and packetize and transmit the packets, and Packet discard notification that detects packet discard, confirms the position of the information included in the discarded packet on the frame, and notifies the encoder of the position information in a video coding transmission system that performs periodic refresh as a refresh target. Means, and periodic refresh adjusting means for changing a next block to be refreshed in the periodic refresh in accordance with position information notified in accordance with packet discarding.

[Action]

An encoder and a decoder for encoding a video signal by an inter-frame prediction method and transmitting the packet by packetizing the same, and a decoder for decomposing a received packet and converting it into a video signal by a corresponding decoding process. Is divided into n blocks, and the blocks are sequentially refreshed and periodically refreshed.
Compensation for errors between frame memories is performed during frame transmission.

According to the present invention, by changing the next refresh target block in the periodic refresh in accordance with the position on the frame of the information included in the discarded packet,
A block corresponding to information lost due to packet discarding can be refreshed.

〔Example〕

FIG. 2 is a block diagram showing an embodiment of an encoder according to the present invention.

In the figure, an input video signal is input to an encoding unit 12 via a subtractor 11, and the encoded signal is input to a decoding unit 13 and sent to a high-speed packet network 15 via a packet transmitting unit 14. Is done. The output of the decoding unit 13 is input to the frame memory 17 via the adder 16. Frame memory
The output of 17 is input to the subtractor 11 and the adder 16. The output of the packet transmission unit 16 is sent to the high-speed packet network 20. The packet receiving unit 18 receives a packet from the high-speed packet network 20, and outputs its output to the periodic refresh control unit 19. The output of the periodic refresh controller 19 is input to the frame memory 17 and the packet transmitter 14.

FIG. 3 is a block diagram showing an embodiment of a decoder according to the present invention.

In the figure, a packet receiving unit 21 is a high-speed packet network 15
, And its output is input to the decoding unit 22, the periodic refresh control unit 23, and the packet discard notification unit 24. The output of the decoding unit 22 is input to the frame memory 26 via the adder 25 and is extracted as an output video signal. The output of the frame memory 26 is input to the adder 25. The output of the periodic refresh controller 23 is input to the frame memory 26. The output of the packet discard notification unit 24 is sent to the high-speed packet network 15 via the packet transmission unit 27.

Hereinafter, the operation of the embodiment will be described with reference to FIG. 2 and FIG.

In the encoder, the subtracter 11 subtracts the video signal (prediction signal) of the previous frame stored in the frame memory 17 from the input video signal, and generates a prediction error signal. This prediction error signal is encoded by the encoding unit 12, and further assembled into a packet by the packet transmission unit 14 and transmitted.

The coded signal input to the decoding unit 13 is decoded into a prediction error signal, and is added to the video signal of the previous frame by the adder 16 to be restored to the input video signal. The restored input video signal is stored in the frame memory 17 for use in inter-frame prediction (creation of a prediction error signal) for the next input video signal.

In the above-described encoding processing of one frame, the periodic refresh control unit 19 resets the value of one block in the frame memory 17. Thereby, for the block, not the prediction error signal but the input video signal is encoded as it is and transmitted to the high-speed packet network 15,
Since the data is also written in the frame memory 17, one block refresh can be performed. As described above, the periodic refresh can be performed by sequentially changing (for example, rotating the blocks in ascending order of the block numbers) every time one frame is processed for the blocks for which the inter-frame prediction is not performed.

Further, the periodic refresh control unit 19 includes a packet transmitting unit.
For each packet 14, control is performed so that each packet has information on a block number, and an identifier indicating the fact is added to a packet including information on a block for which inter-frame prediction has not been performed.

On the other hand, in the decoder shown in FIG. 3, the packet received by the packet receiving section 21 is decomposed and converted into an encoded signal corresponding to a block number to form one frame. If there is no encoded signal corresponding to the block number due to packet discarding, a predetermined value (for example, all “0”) is assigned to form one frame.

This coded signal is decoded by the decoding unit 22 to become a prediction error signal, and is added to the video signal (prediction signal) of the previous frame stored in the frame memory 26 by the adder 25, and the reproduced output A video signal is extracted. This output video signal is stored in the frame memory 26 for reproducing the next frame.

When an identifier indicating that inter-frame prediction has not been performed is given to the received packet, the periodic refresh control unit 23 notified from the packet receiving unit 21 transmits the corresponding block of the frame memory 26 to the corresponding block. Reset the value. As a result, the received information of the block is reproduced as it is, and it can be extracted as an output video signal of one frame together with the other blocks reproduced by the predetermined addition processing. By writing the output video signal into the frame memory 26, the corresponding block is refreshed.

Here, when a part of the packet is discarded, the packet receiving unit 21 identifies the discarded block from the lack of the block number, and notifies the packet discarding notifying unit 24 of the discarded block. The packet discard notification unit 24 notifies the encoder of the position of the discarded packet on the frame, that is, the notified block number from the packet transmission unit 27 via the high-speed packet network 15.

The packet receiving unit 18 of the encoder having received the notification notifies the periodic refresh control unit 19 of the block number at which the packet has been discarded. The periodic refresh control unit 19 changes the order of the periodic refresh for the frame memory 17,
Reset the value of the notified block. This allows
During the encoding process of the next frame, the block can be encoded without performing inter-frame prediction.

As described above, when the packet is discarded, the block whose packet has been discarded can be refreshed in the next frame, so that the error of the frame memory between the encoder and the decoder due to the packet discard can be compensated. .

If a plurality of blocks are lost at the same time, the periodic refresh control unit 19 sequentially refreshes a plurality of frames in ascending order of a plurality of block numbers.

The periodic refresh after compensation accompanying the packet discarding described above returns to the normal periodic refresh operation from the block with the next lowest number after the compensated block or the block with the next lowest number after the block refreshed before compensation. .

Also, if compensation takes time due to network delay,
If the frame immediately before the packet discard is displayed repeatedly until the end of compensation, or if encoding is performed on a field-by-field basis, the field where the packet was discarded is replaced with another field and displayed. Deterioration can be reduced.

〔The invention's effect〕

According to the present invention, the next refresh target in the periodic refresh is adjusted according to the packet discard and the corresponding block is refreshed, so that the error between the frame memories due to the packet discard can be promptly compensated.

In addition, since it can be dealt with by changing the refresh order of the periodic refresh, it is possible to avoid an increase in information amount due to compensation,
The present invention can be adopted without any problem in compensation for packet discarding at the time of network congestion.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of the present invention. FIG. 2 is a block diagram showing an embodiment of the encoder. FIG. 3 is a block diagram showing an embodiment of a decoder. FIG. 4 is a diagram showing one frame divided into n blocks. 11 ... Subtractor 12 ... Encoding unit 13, 22 ... Decoding unit 14, 27 ... Packet transmitting unit 15 ... High-speed packet network 16,25 ... Adder 17,23 ... Frame memories 18,21 …… Packet receiving unit 19, 23 …… Periodic refresh control unit 24 …… Packet discard notification unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-58938 (JP, A) JP-A-63-46032 (JP, A) JP-A-57-63978 (JP, A) JP-A-61-1986 114675 (JP, A) JP-A-63-267080 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04L 12/28 H04L 12/56 H04B 14/00-14/08 H04N 7/13-7/137

Claims (1)

(57) [Claims] An encoder and a decoder for encoding a video signal by an inter-frame prediction method, packetizing and transmitting the packet, and dividing each frame memory of the encoder and the decoder into a plurality of blocks. In the video encoding transmission system in which periodic refresh is sequentially performed as a refresh target, packet discarding is detected, the position of the information included in the discarded packet on the frame is recognized, and the position information is notified to the encoder side. Video coding, comprising: packet discarding notifying means; and periodic refresh adjusting means for changing a next block to be refreshed in the periodic refresh in accordance with the position information notified in accordance with the packet discarding. Transmission method.