JVT (Joint Video Team, Video Joint Working Group) was founded in Pattaya in Thailand in December 2001. It consists of two international standardized organizations of ITU-T and ISOs. The work goal of JVT is to develop a new video coding standard to achieve high compression ratio, high image quality, good network adaptability, etc. At present, JVT work has been accepted by ITU-T, and the new video compression coding standard is called H.264 standard, which is also accepted, called the ADVANCED Video Coding standard, which is the MPEG-4. H.264 standard can be divided into three gears: basic grade (its simple version, application face); main grade (using a number of technical measures to increase image quality and increase compression ratio, available for SDTV, HDTV and DVD, etc.); Extended grade (available for video streaming of various networks). H.264 is more than 50% of H.263 and MPEG-4, but also better support for network transmission. It introduces the encoding mechanism for IP packets, which facilitates packet transmission in the network, support streaming of stream of video in the network. H.264 has a strong anti-chance characteristic, adaptable to high packet loss rate, video transmission in a serious radio channel. H.264 supports hierarchical encoding transmission under different network resources, thereby obtaining a smooth image quality. H.264 can be adapted to video transmission in different networks, network affinity. I. H.264 Video Compression System H.264 Standard Compression System consists of two parts: NetWork Abstract Layer, NAL, NETWORK ABSTRACTION LAYER, NAL. The VCL includes VCL encoders and VCL decoders. The main functions are video data compression coding and decoding, which include motion compensation, transform coding, entropy encoding and other compressed units. NAL is used to provide VCL to provide a unified unified interface that is unrelated to the network. It is responsible for encapsulating the video data to transmit it in the network, which uses a unified data format, including a single byte of the header information, multiple bytes Video data with group frames, logical channel signaling, timing information, sequence end signal, etc. The header includes the storage flag and type flag. The storage flag is used to indicate the current data is not a reference frame. Type flags are used to indicate the type of image data. VCL can transfer encoding parameters adjusted in current network conditions.
Second, H.264 features H.264 and H.261, H.263, but also the DCM differential encoding, i.e., mixed coding structure. At the same time, the H.264 introduces new coding methods under the mixed encoded framework, improves coding efficiency, closer to practical applications. H.264 has no cumbersome options, but strikes to "return to basic", which has better compression performance than H.263 , and has the ability to adapt to multiple channels. The H.264 has a wide range of applications, which can meet a variety of different rates, video applications of different situations, with better blending and anti-packet processing capabilities. The basic system of H.264 does not need to use copyright, with open nature, which can adapt to the use of IP and wireless networks, which is of great significance for current Internet transmission multimedia information, mobile network transmission broadband information. Although the H.264 encoded basic structure is similar to H.261, H.263 is similar, but it has been improved in many links, and is now listed below. 1. A variety of better motion estimates high-precision estimates in H.263 with a half pixel estimate, and further use 1/4 pixels or even 1/8 pixels of motion estimation in H.264. That is, the displacement of the real motion vector may be based on 1/4 or even 1/8 pixels. Obviously, the higher the accuracy of the motion vector displacement, the smaller the remaining error of the frame, the lower the transmission code rate, the higher the compression ratio. The 6-order FIR filter is used to obtain a value of 1/2 pixel position in H.264. When the 1/2 pixel value is obtained, the 1/4 pixel value can be obtained by linear interpolation. For the video format of 4: 1: 1, the 1/4 pixel precision of the brightness signal corresponds to 1/8 pixels of the chroma portion. The motion vector is therefore necessary to perform 1/8 pixels of the chroma signal. In theory, if the accuracy of the motion compensation is doubled (eg, from the whole pixel accuracy to 1/2 pixel accuracy), there can be 0.5bit / sample coding gain, but actual verification found that more than 1/8 pixels in motion vectors After that, the system basically has no significant gain, so in H.264, only 1/4 pixel concentration motion vector mode is used instead of using 1/8 pixel accuracy. The multi-macroblock division mode estimates that in the prediction mode of H.264, a macroblock (MB) can be divided into seven different modes, this multi-mode flexible, subtle macroblock division, more in line with the actual image The shape of the moving object, so, 1, 2, 4, 8 or 16 motion vectors can be included in each macroblock. Multi-parameter frame estimates in H.264, multiple parameter frames can be employed, that is, there are a plurality of highly encoded parameter frames in the cache of the encoder, and the encoder selects a better encoding. The effect is used as a parameter frame, and it is pointed out which frame is used to predict, so that it can obtain a better encoding effect than only the previously encoded frame as a predictive frame. 2. Small size 4? 4 integer transformation video compression encoding in the conventional usage unit is 8? 8. In H.264, a small size of 4? 4 is used. Since the size of the conversion block becomes small, the division of the moving object is more accurate. In this case, the amount of calculation during the image transformation process is small, and the connection error of the edge of the moving object is also greatly reduced. When there is a smoothing area in the image, in order not to generate the gradation difference between the blocks caused by small size transformation, H.264 can perform 16 4 contranes of the three-block DCT coefficients of the intra macroblock brightness data. The second 4? 4 transformation, the DC coefficient of 4 4 contractions of chroma data (one of each small piece, a total of 4 DC factors) 2? 2 block transformation. The H.263 not only makes the size of the image transform block, but this transformation is an integer operation, not the implementation, that is, the encoder and the decoder have the same accuracy, and there is no "reverse transform error".
3. More accurate intra predictions in H.264, each pixel in each 4? 4 blocks can be performed intra prediction with different weighted and to perform different weighted and for intra predictions. 4. There are two methods about entropy encoding in unified VLCH.264. Unified VLC (ie UVLC: Universal VLC). UVLC uses an identical code table to encode, and the decoder is easily identified by the prefix of the codeword, and the UVLC can quickly get ridage quickly when the bit is incorrect. Content adaptive binary arithmetic coding (Cabac: Context Adaptive Binary Arithmetic Coding). Its encoding performance is slightly better than UVLC, but the complexity is high. Third, the performance advantage H.264 and MPEG-4, H.263 encoding performance comparison use 6 test rates: 32kbit / s, 10f / s and qcif; 64kbit / s, 15f / s and qcif; 128kbit / S, 15F / S and CIF; 256 kbit / s, 15f / s and qcif; 512 kbit / s, 30f / s and CIF; 1024 kbit / s, 30f / s, and CIF. The test results indicate that H.264 has a better PSNR performance than MPEG and H.263 . The H.264 PSNR is 2dB higher than MPEG-4, which is 3dB higher than H.263 .
Fourth, the new rapid exercise valuation algorithm new rapid exercise valuation algorithm umhexagons (China Patent) is a new algorithm for saving more than 90% of the original fast full search algorithm in H.264, full name "Unsymmetrical-Cross Muti-Hexagon Search", "Unsymmetrical-Cross Muti-HEXAGON SECH", is a whole pixel motion estimate. Since it is encoded in high yard rate large motion image sequences, Under the conditions of maintaining better distortion performance, the amount of compartments is very low and has been officially adopted by H.264 standard.
The H.264 (MPEG-4 Part 10) of ITU and ISO cooperation is possible to be broadcast, communications, and storage media (CD DVD) to become unified standards, most likely to be a standard for broadband interaction new media. my country's source coding standard has not yet developed, pay close attention to the development of H.264, and developing the work of my country's source coding standards is being processed. The H264 standard enables moving image compression techniques to a higher stage, providing high quality image transfer on lower bandwidth is a highlight of H.264. The promotion application of H.264 is higher in the system of video terminal, gatekeepers, gateways, and MCUs, which will force video conferencing soft and hardware equipment in all aspects.
