JVET-W0076 AHG9: Independently coded region output SEI message [B. Choi, S. Wenger, X. Li, S. Liu (Tencent)]
A new SEI message “Independently coded region output SEI message” that carries useful information for individual access and output of an independently coded region is proposed. The proposed SEI message can be used for cropping and outputting one or more specific rectangular regions which may consists of one or more subpictures. When a decoder system tries to early access and use one or more specific rectangular regions by discarding other regions, the information carried by the proposed SEI message can be used for cropping and outputting the rectangular regions which may consist of one or more subpictures. It is asserted that the use cases of the proposed SEI message include immersive media (VR360, point cloud coding) and game/e-sport contents.
This relates to the video decoder interface design, which has been discussed at recent meetings and is further discussed in JVET-W0168 and JVET-W0169.
It was commented that subpictures can be used for a type of similar functionality. This proposal has alternative approaches, such as indicating overlapping independently decodable regions.
This is proposed for VSEI rather than VVC, and is proposed in a way that does not depend on subpictures.
It is further commented that the same functionality might be implemented using subpictures. It is confirmed by othr experts that it is possible to extract multiple subpictures and merge them into a bitstream. This could achieve a similar functionality.
One expert commented that transcoding may be necessary to achieve this when a user requests a certain region.
After review of JVET-W0168/JVET-W0169, it can be concluded that various aspects of this SEI message would rather relate to VDI. It is however claimed by the proponents that the aspect of multiple cropping windows would still remain specific to the video decoder and its output.
The proponent said it would be desirable to specify this in VSEI in a way that would not depend on VVC and thus could also apply to other video coding designs such as AVC and HEVC.
Further study was recommended in the context of VDI, and with regard to the multiple cropping window aspect.