Video decoder with enhanced CABAC decoding
A decoder receives a bitstream containing quantized coefficients representative of blocks of video representative of a plurality of pixels and decodes the bitstream using context adaptive binary arithmetic coding that includes at least two decoding modes, the first mode decoding the bitstream based upon a probability estimate which is based upon at least one of spatially and temporally adjacent syntax element values to a current syntax element being decoded, the second mode decoding the bitstream not based upon a probability estimate based upon other syntax elements to the current syntax element being decoded. The coding decodes the current syntax element using the first mode if the current syntax element is intra-coded and selecting between sets probable modes with different probabilities. The coding decodes the current syntax element using the second mode if the current syntax element is intra-coded and if selecting among one of the second set of probable modes.
1. A decoder that decodes video, wherein:
(a) the decoder is configured to receive a bitstream;
(b) the decoder is configured to decode the bitstream using one of a regular decoding engine and a bypass decoding engine, the regular decoding engine is configured to perform arithmetic decoding using a context and the bypass decoding engine is configured to perform arithmetic decoding which does not use a context;
(c) the decoder is configured to identify a prediction mode of a plurality of prediction modes;
(d) the decoder is configured to decode first information indicating whether a prediction mode of a current block is selected from a first list of prediction modes generated using one or more prediction modes of one or more adjacent blocks of the current block;
(e) in case that the decoder identifies the first information as indicating that the prediction mode of the current block is a most probable mode selected from the first list of prediction modes, the decoder is configured to decode second information used for selecting a prediction mode from the first list of prediction modes using the bypass decoding engine; and
(f) in case that the decoder identifies the first information as indicating that the prediction mode of the current block is not a most probable mode selected from the first list of prediction modes, the decoder is configured to decode third information used for selecting a prediction mode from a second list of prediction modes using the bypass decoding engine.
2. The decoder of claim 1 wherein the first information is identified by a flag.
3. A method of decoding, comprising:
(a) receiving a bitstream;
(b) decoding the bitstream using one of a regular decoding engine and a bypass decoding engine, the regular decoding engine is an engine configured to perform arithmetic decoding using a context and the bypass decoding engine is an engine configured to perform arithmetic decoding which does not use a context; and
(c) identifying a prediction mode of a plurality of prediction modes, wherein
(d) the decoding step includes decoding first information indicating whether a prediction mode of a current block is selected from a first list of prediction modes generated using one or more prediction modes of one or more adjacent blocks of the current block;
(e) in case that the first information indicates that the prediction mode for the current block is a most probable mode selected from the first list of prediction modes, the decoding step includes decoding second information used for selecting a prediction mode from the first list of prediction modes using the bypass decoding engine; and
(f) in case that the first information indicates that the prediction mode of the current block is not a most probable mode selected from the first list of prediction modes, the decoding step includes decoding third information used for selecting a prediction mode from a second list of prediction modes using the bypass decoding engine.