Intra-prediction mode propagation

1. A method of decoding video data, the method comprising:

deriving a first intra-prediction mode for a first block of video data from a second block of video data, wherein the first block of video data was encoded using an inter-prediction mode, and wherein the second block of video data is different than the first block of video data;

decoding the first block of video data using the inter-prediction mode;

determining a second intra-prediction mode for a neighbor block of video data based at least in part on the first intra-prediction mode derived for the first block of video data; and

decoding the neighbor block of video data using the second intra-prediction mode.

2. The method of claim 1 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a collocated block in a second frame, and

wherein deriving the intra-prediction mode further comprises:

locating the collocated block based on a position of the first block of video data; and

deriving the first intra-prediction mode from the collocated block.

3. The method of claim 1 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a reference block in a reference frame, and

wherein deriving the first intra-prediction mode further comprises:

locating the reference block based on a motion vector associated with the first block of video data; and

deriving the first intra-prediction mode from the reference block.

4. The method of claim 3 , wherein the motion vector is a zero motion vector.

5. The method of claim 1 ,

wherein the second block of video data is included in a candidate list of two or more blocks of video data, and

wherein deriving the first intra-prediction mode further comprises:

deriving the first intra-prediction mode from two or more intra-prediction modes associated with the two or more blocks of video data.

6. The method of claim 1 , wherein the first block of video data is a sub-block of video data.

7. The method of claim 1 , wherein the first block of video data includes a plurality of sub-blocks, the method further comprising:

associating the first intra-prediction mode with each of the plurality of sub-blocks.

8. The method of claim 1 , wherein the first block of video data is in a current frame, and wherein the second block of video data is in the current frame.

9. The method of claim 1 , further comprising:

decoding the first block of video data using the inter-prediction mode to form a first prediction;

decoding the first block of video data using the first intra-prediction mode to form a second prediction; and

combining the first prediction and the second prediction as a weighted sum to produce a final prediction for the first block of video data.

10. The method of claim 1 , wherein determining the second intra-prediction mode for the neighbor block of video data based at least in part on the first intra-prediction mode comprises:

determining a most probable mode list, wherein the most probable mode list includes the first intra-prediction mode; and

determining the second intra-prediction mode for the neighbor block of video data from the most probable mode list.

11. An apparatus configured to decode video data, the apparatus comprising:

a memory configured to store a first block of video data encoded using an inter-prediction mode; and

one or more processors in communication with the memory, the one or more processors configured to:

derive a first intra-prediction mode for a first block of video data from a second block of video data, wherein the first block of video data was encoded using an inter-prediction mode, and wherein the second block of video data is different than the first block of video data;

decode the first block of video data using the inter-prediction mode;

determine a second intra-prediction mode for a neighbor block of video data based at least in part on the first intra-prediction mode derived for the first block of video data; and

decode the neighbor block of video data using the second intra-prediction mode.

12. The apparatus of claim 11 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a collocated block in a second frame, and

wherein deriving the first intra-prediction mode, the one or more processors are further configured to:

locate the collocated block based on a position of the first block of video data; and

derive the first intra-prediction mode from the collocated block.

13. The apparatus of claim 11 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a reference block in a reference frame, and

wherein deriving the first intra-prediction mode, the one or more processors are further configured to:

locate the reference block based on a motion vector associated with the first block of video data; and

derive the first intra-prediction mode from the reference block.

14. The apparatus of claim 13 , wherein the motion vector is a zero motion vector.

15. The apparatus of claim 11 ,

wherein the second block of video data is included in a candidate list of two or more blocks of video data, and

wherein deriving the intra-prediction mode, the one or more processors are further configured to:

derive the first intra-prediction mode from two or more intra-prediction modes associated with the two or more blocks of video data.

16. The apparatus of claim 11 , wherein the first block of video data is a sub-block of video data.

17. The apparatus of claim 11 , wherein the first block of video data includes a plurality of sub-blocks, and wherein the one or more processors are further configured to:

associate the first intra-prediction mode with each of the plurality of sub-blocks.

18. The apparatus of claim 11 , wherein the first block of video data is in a current frame, and wherein the second block of video data is in the current frame.

19. The apparatus of claim 11 , wherein the one or more processors are further configured to:

decode the first block of video data using the inter-prediction mode to form a first prediction;

decode the first block of video data using the first intra-prediction mode to form a second prediction; and

combine the first prediction and the second prediction as a weighted sum to produce a final prediction for the first block of video data.

20. The apparatus of claim 11 , wherein to determine the second intra-prediction mode for the neighbor block of video data based at least in part on the first intra-prediction mode, the one or more processors are further configured to:

determine a most probable mode list, wherein the most probable mode list includes the first intra-prediction mode; and

determine the second intra-prediction mode for the neighbor block of video data from the most probable mode list.

21. An apparatus configured to decode video data, the apparatus comprising:

means for deriving a first intra-prediction mode for a first block of video data from a second block of video data, wherein the first block of video data was encoded using an inter-prediction mode, and wherein the second block of video data is different than the first block of video data;

means for decoding the first block of video data using the inter-prediction mode;

means for determining a second intra-prediction mode for a neighbor block of video data based at least in part on the first intra-prediction mode; and

means for decoding the neighbor block of video data using the second intra-prediction mode.

22. A non-transitory computer-readable storage medium storing instructions that, when executed, causes one or more processors of a device configured to decode video data to:

derive a first intra-prediction mode for a first block of video data from a second block of video data, wherein the first block of video data was encoded using an inter-prediction mode, and wherein the second block of video data is different than the first block of video data;

decode the first block of video data using the inter-prediction mode;

determine a second intra-prediction mode for a neighbor block of video data based at least in part on the first intra-prediction mode; and

decode the neighbor block of video data using the second intra-prediction mode.

23. A method of encoding video data, the method comprising:

encoding a first block of video data using an inter-prediction mode;

deriving a first intra-prediction mode for the first block of video data from a second block of video data, wherein the second block of video data is different than the first block of video data; and

determining a second intra-prediction mode for a neighbor block of video data based at least in part on the first intra-prediction mode derived for the first block of video data.

24. The method of claim 23 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a collocated block in a second frame, and

wherein deriving the first intra-prediction mode further comprises:

locating the collocated block based on a position of the first block of video data; and

deriving the first intra-prediction mode from the collocated block.

25. The method of claim 23 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a reference block in a reference frame, and

wherein deriving the first intra-prediction mode further comprises:

locating the reference block based on a motion vector associated with the first block of video data; and

deriving the first intra-prediction mode from the reference block.

26. The method of claim 25 , wherein the motion vector is a zero motion vector.

27. The method of claim 23 ,

wherein the second block of video data is included in a candidate list of two or more blocks of video data, and

wherein deriving the first intra-prediction mode further comprises:

deriving the first intra-prediction mode from two or more intra-prediction modes associated with the two or more blocks of video data.

28. The method of claim 23 , wherein the first block of video data is a sub-block of video data.

29. The method of claim 23 , wherein the first block of video data includes a plurality of sub-blocks, the method further comprising:

associating the first intra-prediction mode with each of the plurality of sub-blocks.

30. The method of claim 23 , wherein the first block of video data is in a current frame, and wherein the second block of video data is in the current frame.

31. The method of claim 23 , further comprising:

encoding the first block of video data using the inter-prediction mode to form a first prediction;

encoding the first block of video data using the first intra-prediction mode to form a second prediction; and

combining the first prediction and the second prediction as a weighted sum to produce a final prediction for the first block of video data.

32. The method of claim 23 , wherein determining the second intra-prediction mode for the neighbor block of video data based at least in part on the first intra-prediction mode comprises:

determining a most probable mode list, wherein the most probable mode list includes the first intra-prediction mode; and

determining the second intra-prediction mode for the neighbor block of video data from the most probable mode list.

33. An apparatus configured to encode video data, the apparatus comprising:

a memory configured to store a first block of video data; and

one or more processors in communication with the memory, the one or more processors configured to:

encode the first block of video data using an inter-prediction mode;

derive a first intra-prediction mode for the first block of video data from a second block of video data, wherein the second block of video data is different than the first block of video data; and

determine a second intra-prediction mode for a neighbor block of video data based at least in part on the first intra-prediction mode derived for the first block of video data.

34. The apparatus of claim 33 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a collocated block in a second frame, and

wherein deriving the first intra-prediction mode, the one or more processors are further configured to:

locate the collocated block based on a position of the first block of video data; and

derive the first intra-prediction mode from the collocated block.

35. The apparatus of claim 33 ,

wherein the first block of video data is in a current frame,

wherein the second block of video data is a reference block in a reference frame, and

wherein deriving the first intra-prediction mode, the one or more processors are further configured to:

locate the reference block based on a motion vector associated with the first block of video data; and

derive the first intra-prediction mode from the reference block.

36. The apparatus of claim 35 , wherein the motion vector is a zero motion vector.

37. The apparatus of claim 33 ,

wherein the second block of video data is included in a candidate list of two or more blocks of video data, and

wherein deriving the first intra-prediction mode, the one or more processors are further configured to:

derive the first intra-prediction mode from two or more intra-prediction modes associated with the two or more blocks of video data.

38. The apparatus of claim 33 , wherein the first block of video data is a sub-block of video data.

39. The apparatus of claim 33 , wherein the first block of video data includes a plurality of sub-blocks, and wherein the one or more processors are further configured to:

associate the first intra-prediction mode with each of the plurality of sub-blocks.

40. The apparatus of claim 33 , wherein the first block of video data is in a current frame, and wherein the second block of video data is in the current frame.

41. The apparatus of claim 33 , wherein the one or more processors are further configured to:

encode the first block of video data using the inter-prediction mode to form a first prediction;

encode the first block of video data using the first intra-prediction mode to form a second prediction; and

combine the first prediction and the second prediction as a weighted sum to produce a final prediction for the first block of video data.

42. The apparatus of claim 33 , wherein to determine the second intra-prediction mode for the neighbor block of video data based at least in part on the first intra-prediction mode, the one or more processors are further configured to:

determine a most probable mode list, wherein the most probable mode list includes the first intra-prediction mode; and

determine the second intra-prediction mode for the neighbor block of video data from the most probable mode list.