Indicating intra-prediction mode selection for video coding using CABAC

An apparatus for decoding video data, the apparatus comprising a video decoder configured to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• perform a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• determine an intra-prediction mode index by comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• select, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the modified intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, the video decoder is configured to select the intra-prediction mode having an intra-prediction mode index that is two greater than the modified intra-prediction mode index;
• and
• decode the current block using the selected intra-prediction mode.

A method of encoding video data, the method comprising:

• determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encoding the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determining, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode index that corresponds to the intra-prediction mode;
• determining a modified intra-prediction mode index, wherein determining the modified intra-prediction mode comprises comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, determining the modified intra-prediction mode index comprises determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index;
• encoding a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

An apparatus for encoding video data, the apparatus comprising a video encoder configured to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encode the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determine an intra-prediction mode index that corresponds to intra-prediction mode;
• determine, based on a mapping of intra-prediction mode indexes to intra-prediction modes, a modified intra-prediction mode index by comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, and wherein the video encoder determines the modified intra-prediction mode index by determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index;
• and
• encode a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

An apparatus for decoding video data, the apparatus comprising:

• means for determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• means for performing a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• means for determining an intra-prediction mode index, wherein the means for determining the intra-prediction mode index comprises means for comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• means for selecting, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, and wherein the means for selecting the intra-prediction mode comprises means for selecting the intra-prediction mode having an intra-prediction mode index that is two greater than the modified intra-prediction mode index;
• and
• means for decoding the current block using the selected intra-prediction mode.

An apparatus for encoding video data, the apparatus comprising:

• means for determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• means for encoding the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• means for determining, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode index that corresponds to the intra-prediction mode;
• and
• means for determining a modified intra-prediction mode index by comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, the means for determining the modified intra-prediction mode index comprises means for determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index;
• and
• means for encoding a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

A non-transitory, computer-readable storage medium having stored thereon instructions that when executed cause one or more processors to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• perform a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• determine an intra-prediction mode index by comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• select, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and greater than or equal to the intra-prediction mode index for the second most probable intra-prediction mode, and wherein the one or more processors select the intra-prediction mode by selecting the intra-prediction mode having an intra-prediction mode index that is two greater than the modified intra-prediction mode index;
• and
• decode the current block using the selected intra-prediction mode.

A non-transitory, computer-readable storage medium having stored thereon instructions that when executed cause one or more processors to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encode the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determine, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode index that corresponds to the intra-prediction mode;
• and
• determine a modified intra-prediction mode index by comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is greater than the intra-prediction mode index for the first most probable intra-prediction mode and greater than the intra-prediction mode index for the second most probable intra-prediction mode, the one or more processors determine the modified intra-prediction mode index comprises determining one of the modified intra-prediction mode indexes that is two less than the intra-prediction mode index;
• encode a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

A method of decoding video data, the method comprising:

• determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• performing a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• determining an intra-prediction mode index wherein determining the intra-prediction mode index comprises comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• selecting, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, selecting the intra-prediction mode comprises selecting the intra-prediction mode having an intra-prediction mode index equal to the modified intra-prediction mode index;
• and
• decoding the current block using the selected intra-prediction mode.

An apparatus for decoding video data, the apparatus comprising a video decoder configured to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• perform a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• determine an intra-prediction mode index by comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• select, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the modified intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the video decoder is configured to select the intra-prediction mode having an intra-prediction mode index equal to the modified intra-prediction mode index;
• and
• decode the current block using the selected intra-prediction mode.

A method of decoding video data, the method comprising:

• determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• performing a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• determining an intra-prediction mode index wherein determining the intra-prediction mode index comprises comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• selecting, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, selecting the intra-prediction mode comprises selecting the intra-prediction mode having an intra-prediction mode index that is one greater than the modified intra-prediction mode index;
• and
• decoding the current block using the selected intra-prediction mode.

An apparatus for decoding video data, the apparatus comprising a video decoder configured to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on a context for the current block;
• perform a context-based adaptive binary arithmetic coding (CABAC) process to determine a received codeword corresponding to a modified intra-prediction mode index;
• determine an intra-prediction mode index wherein determining the intra-prediction mode index comprises comparing the modified intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode;
• select, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode other than the first most probable intra-prediction mode and second most probable intra-prediction mode to use to decode the current block, wherein the selected intra-prediction mode corresponds to the determined intra-prediction mode index, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, wherein when the modified intra-prediction mode index plus one is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, the video decoder is configured to select the intra-prediction mode having an intra-prediction mode index that is one greater than the modified intra-prediction mode index;
• and
• decode the current block using the selected intra-prediction mode.

A method of encoding video data, the method comprising:

• determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encoding the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determining, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode index that corresponds to the intra-prediction mode;
• determining a modified intra-prediction mode index, wherein determining the modified intra-prediction mode comprises comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, determining the modified intra-prediction mode index comprises determining one of the modified intra-prediction mode indexes that is equal to the intra-prediction mode index;
• encoding a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

An apparatus for encoding video data, the apparatus comprising a video encoder configured to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encode the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determine, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode index that corresponds to the intra-prediction mode;
• determine a modified intra-prediction mode index by comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is less than the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, to determine the modified intra-prediction mode index, the encoder is further configured to determine one of the modified intra-prediction mode indexes that is equal to the intra-prediction mode index;
• and
• encode the codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

A method of encoding video data, the method comprising:

• determining a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encoding the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determining, based on a mapping of intra-prediction mode indexes to intra-prediction modes, an intra-prediction mode index that corresponds to the intra-prediction mode;
• determining a modified intra-prediction mode index, wherein determining the modified intra-prediction mode index comprises comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, determining the one of the modified intra-prediction mode indexes comprises determining the modified intra-prediction mode index that is one less than the intra-prediction mode index;
• and
• encoding a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.

An apparatus for encoding video data, the apparatus comprising a video encoder configured to:

• determine a first most probable intra-prediction mode and a second most probable intra-prediction mode for a current block of video data based on an encoding context for the current block;
• encode the current block using an intra-prediction mode other than the first most probable intra-prediction mode and the second most probable intra-prediction mode;
• determine, based on a mapping of intra-prediction mode indexes to intra-prediction modes an intra-prediction mode index that corresponds to the intra-prediction mode;
• determine a modified intra-prediction mode index, wherein determining the modified intra-prediction mode index comprises comparing the determined intra-prediction mode index to an intra-prediction mode index for the first most probable intra-prediction mode and an intra-prediction mode index for the second most probable intra-prediction mode, wherein each of the first most probable intra-prediction mode and the second most probable intra-prediction mode corresponds to a respective intra-prediction mode index, and wherein when the intra-prediction mode index is greater than or equal to the intra-prediction mode index for the first most probable intra-prediction mode and less than the intra-prediction mode index for the second most probable intra-prediction mode, to determine the one of the modified intra-prediction mode indexes, the video encoder is further configured to determine the modified intra-prediction mode index that is one less than the intra-prediction mode index;
• and
• encode a codeword corresponding to the modified intra-prediction mode index by performing a context-based adaptive binary arithmetic coding (CABAC) process.