Reducing context coded and bypass coded bins to improve context adaptive binary arithmetic coding (CABAC) throughput
Techniques for context-adaptive binary arithmetic coding (CABAC) coding with a reduced number of context coded and/or bypass coded bins are provided. Rather than using only truncated unary binarization for the syntax element representing the delta quantization parameter and context coding all of the resulting bins as in the prior art, a different binarization is used and only part of the resulting bins are context coded, thus reducing the worst case number of context coded bins for this syntax element. Further, binarization techniques for the syntax element representing the remaining actual value of a transform coefficient are provided that restrict the maximum codeword length of this syntax element to 32 bits or less, thus reducing the number of bypass coded bins for this syntax element over the prior art.
1. A method for encoding a video sequence in a video encoder to generate a compressed video bit stream, the method comprising:
determining a value of a delta quantization parameter syntax element;
binarizing the value to generate a sequence of bins, wherein the sequence comprises a prefix and a suffix;
context coding the bins of the prefix into the compressed video bit stream with a truncated unary (TU) code with a maximum codeword length selected from a group consisting of 4 and 5; and
bypass coding the bins of the suffix into the compressed video bit stream with an exponential Golomb (EG) code, an order of the EG code is 0.
2. The method of claim 1 , further comprising bypass coding a bin indicating a sign of the value into the compressed video bit stream following the suffix bins.
3. A method for decoding a compressed video bit stream in a video decoder, the method comprising:
context decoding a first sequence of bins from the compressed video bit stream, the first sequence of bins corresponding to a prefix of a binarized value of a delta quantization parameter syntax element represented by a truncated unary code with a maximum codeword length selected from a group consisting of 4 and 5;
debinarizing the first sequence of bins to determine a value of the prefix;
bypass decoding a second sequence of bins from the compressed video bit stream, the second sequence of bins corresponding to a suffix of the binarized value of the delta quantization parameter syntax element represented by a zeroth order exponential Golomb code;
debinarizing the second sequence of bins to determine a value of the suffix; and
combining the prefix and the suffix to yield a value of the delta quantization parameter syntax element.
4. The method of claim 3 , further comprising bypass decoding a bin indicating a sign of the value, wherein the bin is encoded in the compressed video bit stream following the second sequence of bins.