Indicating intra-prediction mode selection for video coding using CABAC

1. 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 greater than or equal to 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 two greater than the modified intra-prediction mode index; and

decoding the current block using the selected intra-prediction mode.

2. The method of claim 1 , further comprising:

determining the context for the current block based at least in part on intra-prediction modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

3. The method of claim 1 , further comprising:

determining a third most probable intra-prediction mode for the current block.

4. The method of claim 1 , 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.

5. The method of claim 1 , 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.

6. 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.

7. The apparatus of claim 6 , wherein the video decoder is further configured to determine the context for the current block based at least in part on intra-prediction modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

8. The apparatus of claim 6 , wherein the video decoder is further configured to determine the context for the current block based at least in part on a size of the current block.

9. The apparatus of claim 6 , 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.

10. The apparatus of claim 6 , 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.

11. The apparatus of claim 6 , wherein the apparatus comprises at least one of:

an integrated circuit;

a microprocessor; and

a wireless communication device that includes the video decoder.

12. 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.

13. The method of claim 12 , further comprising:

determining the encoding context for the current block based at least in part on modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

14. The method of claim 12 , further comprising:

determining a third most probable intra-prediction mode for the current block.

15. The method of claim 12 , 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.

16. The method of claim 12 , 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.

17. 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.

18. The apparatus of claim 17 , wherein the video encoder is further configured to determine the encoding context for the current block based at least in part on modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

19. The apparatus of claim 17 , wherein the video encoder is further configured to determine a third most probable intra-prediction mode for the current block.

20. The apparatus of claim 17 , 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, the video encoder is further configured to determine the modified intra-prediction mode index by determining the modified intra-prediction mode that is equal to the intra-prediction mode index.

21. The apparatus of claim 17 , 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, the video encoder is further configured to determine the modified intra-prediction mode index by determining the modified intra-prediction mode index that is one less than the intra-prediction mode index.

22. The apparatus of claim 17 , wherein the apparatus comprises at least one of:

an integrated circuit;

a microprocessor; and

a wireless communication device that includes the video encoder.

23. 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.

24. The apparatus of claim 23 , further comprising:

means for determining the context for the current block based at least in part on intra-prediction modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

25. The apparatus of claim 23 , further comprising:

means for determining a third most probable intra-prediction mode for the current block.

26. 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.

27. The apparatus of claim 26 , further comprising:

means for determining the encoding context for the current block based at least in part on modes for at least one of a left-neighboring block to the current block and an above-neighboring block to the current block.

28. The apparatus of claim 26 , further comprising:

means for determining a third most probable intra-prediction mode for the current block.

29. 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.

30. 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.

31. 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.

32. The method of claim 31 , 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.

33. 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.

34. The apparatus of claim 33 , 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, to select the intra-prediction mode, the 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.

35. 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.

36. 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.

37. 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.

38. 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.

39. 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.

40. 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.