File format signaling of error mitigation in sub-picture bitstream based viewport dependent video coding

1. A method implemented in a video coding device, the method comprising:

receiving a plurality of sub-picture tracks containing a plurality of video bitstreams including a plurality of sub-picture video signals each containing a sequence of sub-pictures mapped to a spherical video signal, wherein the plurality of sub-picture tracks are compatible with a multi-bitstream merging for reconstruction of the spherical video signal or a part thereof, wherein the plurality of sub-picture tracks are compatible with a multi-bitstream merging when no sample values outside a sub-picture are referenced for inter-prediction, motion vectors are restricted to point to full-sample locations inside the sub-picture and to fractional-sample locations that employ only full-sample locations inside the sub-picture for interpolation, and inter-prediction is restricted so motion vector candidates for temporal motion vector prediction are not derived from blocks outside the sub-picture;

parsing one or more track level mergable indications from the bitstream for each of the sub-picture tracks, the track level mergable indications indicating whether a video bitstream carried in a current sub-picture track can be merged with a video bitstream carried in the sub-picture tracks in a same track group; and

decoding the plurality of sub-picture tracks based on the track level mergable indications.

2. The method of claim 1 , wherein the track level mergable indications includes a track_mergable_with_other_video_tracks flag that, when set, indicates that the video bitstream carried in the current sub-picture track can be merged with one or more other of the plurality of video bitstreams carried in one or more other of the plurality of sub-picture tracks to generate a single video bitstream without decoding mismatch by rewriting only header data of the video bitstreams.

3. The method of claim 1 , wherein the track level mergable indications are included in a track header box in a track box for each track containing one of the video bitstreams.

4. The method of claim 1 , wherein the track level mergable indications are included in a track group box describing associations between the sub-picture tracks including the video bitstreams.

5. The method of claim 1 , wherein the track level mergable indications are included in a media box describing track media information.

6. The method of claim 1 , wherein the track level mergable indications, when set, further indicate that wavefront parallel processing is disabled by setting an entropy_coding_sync_enabled_flag to zero in picture parameter sets (PPSs) for the sub-picture tracks including the video bitstreams.

7. The method of claim 1 , wherein the track level mergable indications are included in a track level box.

8. The method of claim 1 , further comprising applying a multi-bitstream merge function to merge the sequences of sub-pictures into the spherical video signal for display via a viewport of a virtual reality rendering device.

9. The method of claim 8 , wherein the multi-bitstream merge function is a lightweight merging function that does not change block level coding results for the sub-pictures.

10. The method of claim 1 , wherein the sequences of sub-pictures are coded according to a High Efficiency Video Coding (HEVC) based viewport-dependent Omnidirectional Media Format (OMAF) video profile.

11. A video coding device comprising:

a receiver configured to receive a plurality of sub-picture tracks containing a plurality of video bitstreams including a plurality of sub-picture video signals each containing a sequence of sub-pictures mapped to a spherical video signal, wherein the plurality of sub-picture tracks are compatible with multi-bitstream merging for reconstruction of the spherical video signal or a part thereof, wherein the plurality of sub-picture tracks are compatible with a multi-bitstream merging when no sample values outside a sub-picture are referenced for inter-prediction, motion vectors are restricted to point to full-sample locations inside the sub-picture and to fractional-sample locations that employ only full-sample locations inside the sub-picture for interpolation, and inter-prediction is restricted so motion vector candidates for temporal motion vector prediction are not derived from blocks outside the sub-picture; and

a processor coupled to the receiver and configured to:

parse one or more track level mergable indications from the bitstream for each of the sub-picture tracks, the track level mergable indications indicating whether a video bitstream carried in a current sub-picture track can be merged with a video bitstream carried in the sub-picture tracks in a same track group; and

decode the plurality of sub-picture tracks based on the track level mergable indications.

12. The video coding device of claim 11 , wherein the track level mergable indications includes a track_mergable_with_other_video_tracks flag that, when set, indicates that the video bitstream carried in the current sub-picture track can be merged with one or more other of the plurality of video bitstreams carried in one or more other of the plurality of sub-picture tracks to generate a single video bitstream without decoding mismatch by rewriting only header data of the video bitstreams.

13. The video coding device of claim 11 , wherein the track level mergable indications are included in a track header box in a track box for each track containing one of the video bitstreams.

14. The video coding device of claim 11 , wherein the track level mergable indications are included in a track group box describing associations between the sub-picture tracks including the video bitstreams.

15. The video coding device of claim 11 , wherein the track level mergable indications are included in a media box describing track media information.

16. The video coding device of claim 11 , wherein the track level mergable indications, when set, further indicate that wavefront parallel processing is disabled by setting an entropy_coding_sync_enabled_flag to zero in picture parameter sets (PPSs) for the sub-picture tracks including the video bitstreams.

17. A non-transitory computer readable medium comprising a computer program product for use by a video coding device, the computer program product comprising computer executable instructions stored on the non-transitory computer readable medium such that when executed by a processor cause the video coding device to:

receive a plurality of sub-picture tracks containing a plurality of video bitstreams including a plurality of sub-picture video signals each containing a sequence of sub-pictures mapped to a spherical video signal, wherein the plurality of sub-picture tracks are compatible with a multi-bitstream merging for reconstruction of the spherical video signal or a part thereof, wherein the plurality of sub-picture tracks are compatible with a multi-bitstream merging when no sample values outside a sub-picture are referenced for inter-prediction, motion vectors are restricted to point to full-sample locations inside the sub-picture and to fractional-sample locations that employ only full-sample locations inside the sub-picture for interpolation, and inter-prediction is restricted so motion vector candidates for temporal motion vector prediction are not derived from blocks outside the sub-picture;

parse one or more track level mergable indications from the bitstream for each of the sub-picture tracks, the track level mergable indications indicating whether a video bitstream carried in a current sub-picture track can be merged with a video bitstream carried in the sub-picture tracks in a same track group; and

decode the plurality of sub-picture tracks based on the track level mergable indications.

18. The non-transitory computer readable medium of claim 17 , wherein the track level mergable indications includes a track_mergable_with_other_video_tracks flag that, when set, indicates that the video bitstream carried in the current sub-picture track can be merged with one or more other of the plurality of video bitstreams carried in one or more other of the plurality of sub-picture tracks to generate a single video bitstream without decoding mismatch by rewriting only header data of the video bitstreams.

19. The non-transitory computer readable medium of claim 17 , wherein the track level mergable indications are included in a track header box in a track box for each track containing one of the video bitstreams.

20. The non-transitory computer readable medium of claim 17 , wherein the track level mergable indications are included in a track group box describing associations between the sub-picture tracks including the video bitstreams.