"H.264 / AVC Video Code Technology Detailed" video tutorial has been on "CSDN", which details the background, standard protocol and implementation of H.264, and through a practical engineering form to H.264 Standard analysis and implementation, welcome to watch!
"The paper is very shallow, perceived this matter", only the standard document is operated in the form of code, in order to have a sufficient understanding and understanding of the video compression coding standards!
Link address: H.264 / AVC video codec technology detailed
GitHub code address: Click here
H.264 in the strip (the Slice)
1. Slice the concept of
We already know that the entire H.264 bit stream structure can be divided into two layers: a network abstraction layer (NAL) video coding layer VCL. In the NAL layer of the H.264 bit stream as a series of NAL Units, different NAL Units contains different types of syntax elements. In the foregoing two parsed sequence parameter set SPS and the picture parameter set PPS is one of two important portions, which contains some generic parameters control the decoding process.
The actual original video image data are stored in the storage portion VCL NAL Units other layer. This part is called the data slice (the Slice) in the bit stream. A Slice comprises a part or all of the image data, in other words, a video image may be encoded as one or several Slice. Slice contains a minimum of one macro block, containing the most data of the entire frame image. In various implementations of coding, the number of images in the same frame Slice constituted not necessarily the same.
Slice of design in H.264 main purpose is to prevent the spread of errors. Because the different slice, which is independent of the decoding operation. A decoding process for a slice of the reference data (e.g., predictive encoding) can not cross the boundary of the slice.
2. Slice types
The different data stream types, H.264 Standard defines Slice Total Type 5:
I slice: intra-coded bands; P slice: unidirectional interframe coding by strip; B slice: bidirectional interframe coded strip; SI slice: I slices handover, extended profile for use in stream switching ; SP slice: switching P slice, extended profile for use in stream switching;
In Slice I contains only I macroblocks, not contain P or B macroblock; P-Slice and B, in addition to the respective P-type macroblocks and B, may also contain I-type macroblocks.
3. Slice composition
Overall Slice each composed of two parts, as part of the Slice header, for storing general information of Slice (Slice type such as the current, etc.), another part of the body Slice, usually a set of consecutive macroblocks structure (or macroblock skip information), as shown below:
4. Slice Header structure
Slice header stored in the main current slice some global information, slice body macroblocks need to rely on such information during decoding. Some of the more common syntax elements are:
first_mb_in_slice: current slice contains a first macroblock position in the entire frame; slice_type: the type of the current slice; pic_parameter_set_id: slice depends pps id of current; colour_plane_id: separate_colour_plane_flag when the flag is true, colour_plane_id represents the current color components, each represent 0, 1 Y, U, V components. frame_num: a measure that represents the current frame number of ways. field_pic_flag: field coding flag. It indicates that the current frame is encoded as slice when the flag is 0; when the flag to indicate the current time slice is encoded as a field. bottom_field_flag: bottom field flag. The flag 1 indicates that the current slice is a bottom field of a frame; 0 indicates a top field of the current slice of a frame. idr_pic_id: represents the number of IDR frames. A certain slice all IDR frame belongs, which idr_pic_id should be consistent. This value is in the range [0,65535]. pic_order_cnt_lsb: another measurement that represents the current frame number of ways. delta_pic_order_cnt_bottom: Calculation indicates the top field and bottom field difference POC, not present the default is 0; slice_qp_delta: qp for calculating the initial value within the current slice is used.
The entire structure of the slice header shown in the following table:
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