H.264 Analysis of QoS characteristics of video encoding transmission (II)

III. H. 264 of the video encoding layer error recovery [] In H.261, H.263, MPEG-1, MPEG-2, many error recovery tools have been well applied: different formats of image segmentation (slices and block groups), I-mode macro blocks, slices and image interpolation, select reference images (with and without feedback, image level, GoB/slice or MB level), and separate data. H.264 inherits some excellent error recovery tools from earlier video encoding standards, and also improves and innovates a variety of error recovery tools. This section describes H.264's error recovery tools, including parameter sets, flexible macro block sorting, and redundant slice Rs.

1. The parameter set is a new concept of H.264 standard. It is a method to enhance error recovery by improving the video code stream structure. H.264 parameter sets are further divided into sequence parameter sets and image parameter sets. The sequence parameter set includes all the information of an image sequence, that is, all the image information between two IDR images. The image parameter set includes all the relevant information of all parts of an image, including the image type and serial number. The loss of some serial numbers during decoding can be used to check whether the information package is lost or not. Multiple different sequences and image parameter sets are stored in the decoder. The encoder selects an appropriate parameter set based on the storage location of the header of each encoding shard, the image parameter set itself also contains reference information about the sequence parameter set used. As we all know, the loss of some key information bits (such as the sequence and image header information) will cause serious negative effects of decoding, while H. 264 separate the key information and ensure correct transmission in an error-prone environment based on the design of the parameter set. The design of this code stream structure undoubtedly enhances the error recovery capability of the code stream transmission. The specific implementation methods of the parameter set are also diverse: (1) through out-of-band transmission, This method requires the parameter set to be transmitted to the decoder before the first encoding arrives through a reliable protocol; (2) Pass in-band transmission, which requires more advanced protection for the parameter set. For example, send a copy package to ensure at least one target is reached. (3) hardware processing parameter sets are used in encoder and decoder. 2. A piece, a group, and a FMO image are composed of several pieces, each of which contains a series of macro blocks (MB ). The MB sorting can be in the grating scan order, or not in the scan order. Each piece is decoded independently. The macro blocks of different pieces cannot be used for prediction reference in their own films. Therefore, slice settings do not cause the spread of codes. The flexible macro block sorting FMO is a major feature of H.264 and is suitable for the basic and extended grades of H.264. The internal prediction mechanism of an image, such as intra-frame prediction or motion vector prediction, allows only adjacent macro blocks of space in the same group. FMo uses Macro Block allocation ing technology to allocate each macro block to a film that is not in scan order. The FMO mode divides various image modes, including the chessboard mode and the rectangle mode. Of course, the FMO mode can also split the Macro Block in one frame in sequence, so that the size of the split piece is smaller than the MTU size of the wireless network, and the image data after the FMO mode is separated for transmission. All the MB values are divided into two groups: 0 and 1, which are marked in yellow and white respectively. When the white chip is lost, because the macro blocks around it all belong to the macro blocks of other slices, some weighting of the yellow chip macro block can be used to replace the corresponding macro blocks of the white chip by using the neighborhood correlation. This error hiding mechanism can significantly improve the anti-code performance. Experiments show that when the packet loss rate reaches 10% in a CIF video conference, video distortion is as low as that of trained eyes. The cost of using FMO is slightly lower encoding efficiency (because it breaks the prediction between non-neighbor MB), and there is a high latency in a highly optimized environment.

3. Data Segmentation

Generally, the data of a macro block is stored together to form a piece. Data Division re-combines the macro block data of a piece, the Macro Block semantic-related data is divided into parts. H.264 the video encoding standard uses three different types of data segmentation. (1) A-type segmentation is the header information division, including macro block types, quantization parameters, and motion vectors. This information is the most important. (2) B-type segmentation refers to intra-frame Information Division, including intra-frame cbps and intra-frame coefficients. Intra-frame information can prevent the spread of errors. This type of data segmentation requires that the-type segmentation of a given shard be effective. Compared with inter-frame information, intra-frame information can better prevent the drift effect, therefore, it is more important than inter-frame splitting. (3) c-type segmentation C-type segmentation refers to information division between frames, including the cbps between frames and the coefficient between frames. Generally, it is the maximum partition of the encoding part. Inter-frame segmentation is the least important, and its use requires a-type segmentation to be effective. When data separation is used, the source encoder arranges different types of separation in three different buffers, and the size of the split must be adjusted to ensure that it is smaller than the MTU length, therefore, it is an encoder rather than nal to achieve data segmentation. On the decoder, all shards are used for information reconstruction. In this way, if the information in or between frames is lost, the valid frame header information can still be used to improve the error hiding efficiency, that is, the valid macro block type and motion vector, the basic features of macro blocks are retained, so that a fairly high information reconstruction quality is still available, and only detailed information is lost.

4. Redundant chip Method

H. 264 when the decoder receives lost or damaged image information in a feedback-based system, select the correct reference Macro Block in the reference image sequence for error recovery. For systems without feedback, H. 264 redundant part encoding is proposed. Redundant fragment allows encoder to add one or more redundant representations of the same MB to the same bitstream. It should be noted that the encoding parameters of these redundant parts are different from those of non-redundant parts. For example, the primary part can be encoded with low QP (high quality), while the redundant information can use a high QP (low quality) in this way, the quality is rough but the bit rate is lower. When refactoring, the decoder first uses the primary chip. If it is available, the redundant chip is discarded. If the primary chip is lost (for example, because of packet loss), the redundant chip can also be used for refactoring. Redundancy is mainly used in mobile environments that support high-error codes. 5. intra-frame encoding H. in 264, the intra-frame encoding is basically similar to the previous video encoding standard, but it has also been improved mainly because: (1) h. in 264, the reference macro block of intra-Frame Prediction macro block can be an inter-frame encoding macro block. The intra-Frame Prediction macro block is not the same as the intra-frame encoding in H.263, the predicted intra-frame encoding method is more efficient than the non-predicted intra-frame encoding method, but it reduces the re-synchronization performance of intra-frame encoding, you can set the intra-Frame Prediction flag to restore this performance. (2) There are two types of clips that only contain intra-frame macro blocks, one is intra-frame (I slice), and the other is instant refresh (IDR slice ). The image to be refreshed immediately must exist in the image to be refreshed immediately (IDR picture. Compared with short-term reference images, instant image refresh provides stronger re-synchronization performance. H. 264 improve the re-synchronization performance of intra-frame images by optimizing the encoding of cost distortion and setting the intra-Frame Prediction mark. 264 Analysis of QoS characteristics of video encoding transmission (1) about h. 264 Analysis of QoS characteristics of video encoding transmission (2) about h. 264 Analysis on QoS characteristics of video encoding transmission (III)