Method for decoding video from video bitstream, method for encoding video, video decoder, and video encoder

A method for encoding a video, the method comprising:

• accessing a partition of the video, the partition comprising a plurality of coding tree units (CTUs) forming one or more CTU rows;
• processing the partition of the video to generate a binary representation of the partition, the processing comprising:
• for each CTU of the plurality of CTUs in the partition, determining whether to commence an initialization process;
• and
• in response to commencing the initialization process;
• determining whether the CTU is a first CTU in a slice or a tile;
• in response to determining that the CTU is the first CTU in a slice or a tile, initializing context variables for context-adaptive binary arithmetic coding (CABAC) according to a first context variable initialization process;
• in response to determining that the CTU is not the first CTU in a slice or a tile, determining whether parallel decoding is enabled and the CTU is the first CTU in a CTU row of a tile;
• in response to determining that the parallel decoding is enabled and the CTU is the first CTU in a CTU row of a tile,
• determining an available flag for a top neighboring block of the CTU,
• in response to determining that the available flag for the top neighboring block of the CTU indicates that the top neighboring block is available, initializing the context variables according to a second context variable initialization process, and
• in response to determining that the available flag for the top neighboring block of the CTU indicates that the top neighboring block is not available, initializing the context variables according to the first context variable initialization process;
• in response to determining that the parallel decoding is not enabled or the CTU is not the first CTU in a CTU row of a tile, no initialization is performed for the context variables;
• and
• encoding the CTU, comprising encoding coefficient values of the transform units (TUs) in the CTU into a binary representation based on the context variables;
• and
• encoding the binary representation of the partition into a bitstream of the video.

A non-transitory computer-readable medium storing computer programs and a bitstream, wherein when executed by a processor, the computer programs cause the processor to perform an encoding method to generate the bitstream, the encoding method comprising:

• accessing a partition of a video, the partition comprising a plurality of coding tree units (CTUs) forming one or more CTU rows;
• processing the partition of the video to generate a binary representation of the partition, the processing comprising:
• for each CTU of the plurality of CTUs in the partition, determining whether to commence an initialization process;
• and
• in response to commencing the initialization process;
• determining whether the CTU is a first CTU in a slice or a tile;
• in response to determining that the CTU is the first CTU in a slice or a tile, initializing context variables for context-adaptive binary arithmetic coding (CABAC) according to a first context variable initialization process;
• in response to determining that the CTU is not the first CTU in a slice or a tile, determining whether parallel decoding is enabled and the CTU is the first CTU in a CTU row of a tile;
• in response to determining that the parallel decoding is enabled and the CTU is the first CTU in a CTU row of a tile,
• determining an available flag for a top neighboring block of the CTU,
• in response to determining that the available flag for the top neighboring block of the CTU indicates that the top neighboring block is available, initializing the context variables according to a second context variable initialization process, and
• in response to determining that the available flag for the top neighboring block of the CTU indicates that the top neighboring block is not available, initializing the context variables according to the first context variable initialization process;
• in response to determining that the parallel decoding is not enabled or the CTU is not the first CTU in a CTU row of a tile, no initialization is performed for the context variables;
• and
• encoding the CTU, comprising encoding coefficient values of the transform units (TUs) in the CTU into a binary representation based on the context variables;
• and
• encoding the binary representation of the partition into a bitstream of the video.