Video compression coding technology makes multimedia conferences go further

[Audio Network Information]

Under the rapid development of the Internet and mobile communications industry, the research on IP and wireless mobile technologies is accelerated, which not only ensures the quality of video signals after video compression, but also has strong anti-error error correction capability. To this end, ITU-T and ISO established the Joint Video Experts Group (JVT) and in March 2003 passed the H.264/AVC video coding standard. Below, the video conference system famous brand Chenlian video conference system for you to introduce in detail.

The goals set at the time had the following two main points.

(a) The video compression ratio is twice that of H.263 and MPEG-4;

(b) Good adaptability to networks, especially IP and wireless networks. A large number of simulation tests show that H.264/AVC has achieved the desired goal, and H.264/AVC has been recognized as the next generation video coding standard.

H.264/AVC takes a series of adaptive measures against the variety of video content (sometimes more details, sometimes flat, sometimes active, sometimes slow), compared to traditional H.263, MPEG-4 Etc., the video compression ratio has been significantly improved. There are:

(a) Adaptive selection of field and frame coding: Since the spatial correlation between adjacent lines in a frame is strong, and the temporal correlation between adjacent lines in a field is strong, frame coding is used for video coding with small motion amount, and Normal coding is used for video coding with a large amount of motion, that is, image adaptive frame/field coding (PAFF); if a frame contains some mixed regions, the existing regions are large in motion and others are small in motion. Macroblock adaptive frame/field (MBAFF) coding has then appeared.

(b) Motion compensation (MC) of the variable size block: H.264 uses 16×16 macroblocks for the flat area, while the detail area uses 8×8 or even 4×4 macroblocks, so the prediction accuracy is higher than the previous standard. High, adaptable to videos with ever-changing content.

(c) Motion compensation for sub-pixels (MC): H.264 increases the accuracy of motion vectors to 1/2 or even 1/4 pixels, and further reduces the complexity of interpolation processing, which improves prediction accuracy. It improves the video compression ratio.

(d) The number of reference frames in MC:H.264 of multiple reference frames can be increased to 5, up to even 15. As a result, the accuracy of the MC is significantly improved.

(e) Intra-frame coding: Directional space prediction is used, that is, the directed spatial prediction of the decoded domain is referred to, and the prediction of the transform domain is not used, which improves the prediction quality.

(f) Integer transform: Integer transform is adopted in H.264 to achieve accurate matching between transform and inverse transform, which improves video quality.

(g) Adaptive Entropy Coding: The video signal is further compressed by adaptively performing variable length coding or technical coding according to the encoded neighboring pixels.

(f) Loop deblocking filtering: Introducing deblocking filtering into the MC prediction loop not only removes the block effect, but also protects the details and edges of the video image, thus improving the subjective and objective quality of the image.

Thanks to a series of intricate technical measures, compared with the previous standards, although there are no major changes, it has surprisingly improved the video compression ratio.

H.264 is still being improved, and it is believed that there are still room for improvement in its algorithm. The current LSI technology can compensate for the complexity caused by the improved algorithm.

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