H.264 is the same as the previous standard, it is still a hybrid coding framework. The AVS video standard uses a similar technical framework to H.264, including transformation, quantization, entropy coding, intra prediction, inter prediction, and loop filtering. Wait for the module. The differences in their core technologies include the following: 1. Transformation and Quantization H.264 uses block-based transform coding for the residual data to remove the spatial redundancy of the original image, so that the image capacity is concentrated on a small part of the coefficient. The DC coefficient value is generally the largest, which can improve the compression ratio and enhance the resistance. Interference ability. The previous standard generally uses DCT transformation. The disadvantage of this transformation is that there will be a mismatch. The original data will have a difference after transformation and inverse transformation recovery, because it is also a large amount of calculation. H.264 uses an integer transform based on 4 & TImes; 4 blocks. AVS uses integer conversion of 8 & TImes; 8, which can be realized without mismatch on 16-bit processors. The de-correlation of high-resolution video images is more effective than 4 & TImes; 4 transformation. It adopts 64-level quantization, which can adapt to the requirements of different applications and services on code stream and quality. Second, intra prediction Both H.264 and AVS technologies use intra prediction, predict the current block with adjacent pixels, and use multiple prediction modes that represent spatial domain textures. H.264 brightness prediction has 4 prediction modes: 4 blocks and 16 × 16 blocks. For 4 × 4 blocks: from -135 degrees to +22.5 degrees plus a DC prediction, there are 9 prediction directions; for 16 × 16 block: There are 4 prediction directions. Chrominance prediction is 8 × 8 blocks, there are 4 prediction modes, similar to the 4 modes of intra 16 × 16 prediction, where DC is mode 0, horizontal is mode 1, vertical is mode 2, and plane is mode 3. 3. Inter prediction H.264 inter prediction is a prediction mode that uses encoded video frames and block-based motion compensation. The difference from the previous standard inter prediction is the wider block size range, the use of sub-pixel motion vectors, and the use of multiple reference frames. H.264 has 16 × 16, 16 × 8, 8 × 16, 8 × 8, 8 × 4, 4 × 8 and 4 × 4. There are 8 macroblock and sub-macroblock divisions, while AVS only has 16 × 16, 16 There are 4 kinds of macroblock division methods in total: × 8, 8 × 16 and 8 × 8. H.264 supports using multiple different reference frames to predict inter-frame macroblocks and slices. In AVS, P frames can use up to 2 frames of forward reference frames, and B frames use one reference frame before and after each. Four, entropy coding H.264 has formulated the entropy coding efficiency based on the amount of information. One is to use uniform variable length coding (UVLC) for all the symbols to be coded, and the other is to use content-based adaptive binary arithmetic coding (CABAC, Context-Adaptive Binary Arithmetic Coding), which greatly reduces the correlation redundancy of block coding and improves coding efficiency. The calculation complexity of UVLC is relatively low, which is mainly aimed at the application with strict coding time. The disadvantage is low efficiency and high code rate. CABAC is a very efficient entropy coding method, and its coding efficiency is 50% higher than UVLC coding. AVS entropy coding uses adaptive variable length coding technology. In the AVS entropy coding process, all syntax elements and residual data are mapped into a binary bit stream in the form of exponential Golomb codes. The advantage of adopting exponential Columbus code is that on the one hand, its hardware complexity is relatively low, and the code can be parsed according to the closed formula, without looking up the table; on the other hand, it can be flexibly determined according to the probability distribution of the coding element. For coding, if K is selected properly, the coding efficiency can approach the information entropy. The block transformation coefficients of the prediction residuals are scanned to form (level, run) pairs. Level and run are not independent events, but there is a strong correlation. In AVS, level and run are coded in two dimensions and are based on The different probability distribution trends of the current level and run adaptively change the order of the exponential Golomb code. In addition, there are no SI and SP frames in AVS. It can be said that AVS was developed on the basis of H.264, absorbing the essence of H.264, but in order to bypass the troubles of patents, it had to give up some core algorithms of H.264. The trade-off is that the complexity is greatly reduced when the coding efficiency is slightly reduced.
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