Acceleration of context adaptive binary arithmetic coding (CABAC) in video CODECS
A method is provided for determining a context-index when performing Context-based Adaptive Binary Arithmetic Coding (CABAC) for video compression or decompression includes initializing to an initialized value each of a plurality of context-indexes of chosen syntax elements associated with a given block (e.g., a macroblock). The context-index of dependent neighboring blocks of the given block is evaluated. The dependent neighboring blocks are blocks that have a context-index that depends on coding of a current bin position. The context-index of the dependent neighboring blocks is updated if and only if their context-index changes from the initialized values.
1. A method of determining a context-index when performing Context-based Adaptive Binary Arithmetic Coding (CABAC) for video compression or decompression, the method comprising:
initializing to an initialized value each of a plurality of context-indexes of chosen syntax elements associated with given blocks, the given blocks including at least two next rows of blocks to be coded;
evaluating the context-index of dependent neighboring blocks of a first block in the given blocks prior to coding of the neighboring blocks, the dependent neighboring blocks being blocks that have a context-index that depends on the coding of a current bin position within the first block; and
updating the context-index of the dependent neighboring blocks from the initialized values while coding the first block and prior to coding of the dependent neighboring blocks.
2. The method of claim 1 , wherein the selected syntax elements are specified in an H.264/MPEG 4 AVC standard and are selected from the group consisting of a mb_type, mb_skip_flag, transform_size_8×8_flag, mb_qp_delta, mb_field_decoding_flag, intra_chroma_pred_mode, mvd (horizontal)_l0, mvd (vertical)_l0, mvd (horizontal)_l1, mvd (vertical)_l1, ref_idx_l0 and ref_idx_l1, coded_block_pattern and coded_block_flag.
3. The method of claim 1 , wherein the selected syntax elements are specified in a HEVC standard and are selected from the group consisting of a split_cu_flag, cu_skip_flag, sig_coeff_flag if the video compression or decompression performed using HEVC.
4. The method of claim 1 , wherein the context-index of the dependent neighboring blocks only depends on the coding of a current bin position within the given blocks when at least one specified condition is satisfied, one of the specified conditions being dependent on the block type.
5. The method of claim 1 , wherein initializing the plurality of context-indexes includes selectively initializing all context-indexes to a minimum possible context-index for the selected syntax element being coded or to a maximum possible context-index for the selected syntax element being coded.
6. The method of claim 5 , wherein initializing and updating the context-index of the dependent neighboring blocks includes incrementing the context-index based on block type and a bit rate of a video stream being compressed or decompressed.
7. The method of claim 5 , wherein initializing and updating the context-index of the dependent neighboring blocks includes decrementing the context-index based on block type and a bit rate of a video stream being compressed or decompressed.
8. A CABAC encoder, comprising:
a binarization module for converting a syntax element into a sequence of bins;
a context-index module for obtaining one or more context models for the syntax element based on the sequence of bins, each of the context models being associated with a context model, wherein the context-index module obtains the one or more context models by initializing a context-index of the syntax element associated with given blocks including at least one two next rows of blocks to be coded and evaluates the context-index of dependent neighboring blocks of a first block in the given blocks prior to coding of the dependent neighboring blocks, the dependent neighboring blocks being blocks that have a context-index that depends on the coding of a current bin position within the first block of the given blocks; and
an arithmetic encoder for updating the one or more context models based on the sequence of bins and using the one or more context models to encode each of the bins in the sequence, wherein the arithmetic encoder updates the one or more context models by updating the associated context-indices of the dependent neighboring blocks while coding the first block and prior to coding of the dependent neighboring blocks, when their context-indices changes from the initialized values.
9. The CABAC encoder of claim 8 , wherein the context-index module is further configured to assign a context model to each bin the sequence of bins.
10. The CABAC encoder of claim 8 , wherein the context-index of the dependent neighboring blocks only depends on the coding of a current bin position within the given blocks when at least one specified condition is satisfied, one of the specified conditions being dependent on the block type.
11. The CABAC encoder of claim 8 , wherein the context-index module is further configured to initialize the plurality of context-indexes by selectively initializing all context-indexes to a minimum possible context-index for the selected syntax element being coded or to a maximum possible context-index for the selected syntax element being coded.
12. The CABAC encoder of claim 11 , wherein the context-index module is further configured to initialize and update the context-index of the dependent neighboring blocks by incrementing the context-index based on macroblock type and a bit rate of a video stream being compressed or decompressed.
13. The CABAC encoder of claim 11 , wherein the context-index module is further configured to initialize and update the context-index of the dependent neighboring blocks by decrementing the context-index based on block type and a bit rate of a video stream being compressed or decompressed.
14. A method of debinarizing Context-based Adaptive Binary Arithmetic Coding (CABAC) data during video decompression, the method comprising:
identifying all coded syntax elements in an arrangement, and which are coded with a specific bit pattern and bit length that is pre-defined by a protocol;
rearranging the codes of the syntax elements that are identified such that the codes with an equal number of bits are arranged sequentially without any intervening codes having a different number of bits; and
performing de-binarization using the rearranged codes of the syntax elements.
15. The method of claim 14 , wherein performing the de-binarization comprises:
checking if a number of decoded bins in a bin string formed during the decoding of one of the syntax elements can result in a valid syntax element;
if the said number of decoded bins can potentially yield a valid syntax element, searching only those sequentially arranged codes that contain the given number of bins; and
identifying a valid syntax element that matches the bin string formed during the decoding of the syntax element.
16. The method of claim 14 , wherein the protocol conforms to an H.264/MPEG 4 AVC standard.
17. The method of claim 1 , further comprising:
identifying the chosen syntax elements which are coded with a specific bit pattern and bit length that is pre-defined by a protocol;
arranging the codes of the identified syntax elements that are identified such that the codes with an equal number of bits are arranged sequentially without any intervening codes having a different number of bits; and
performing de-binarization using the arranged codes of the identified syntax elements.