[FS_AVFOPS_MED] Updates to possible solutions and mapping to scenarios
This CR updates the possible solutions related to new use cases, specifically adding solutions for Scenario #5: Video with changeable background.
The CR extends Table 6.0-1 to include two new solutions for Scenario #5:
These solutions address video with changeable background use cases.
This solution leverages HEVC multi-layer extensions to carry alpha planes as auxiliary channels:
Auxiliary Picture Signalling:
- Uses scalability_mask_flag in the Video Parameter Set (VPS)
- Sets scalability mask index to '3' (reserved for "Auxiliary" scalability dimension)
- AuxId value determines auxiliary picture type:
- AuxId = 1: Alpha plane (AUX_ALPHA)
- AuxId = 2: Depth picture (AUX_DEPTH)
- Additional interpretation information carried via SEI messages (Alpha channel information, Depth representation information)
Two possible approaches identified for further study:
1. Multiview profiles (though only one view is present)
2. Combination of non-Multiview profile for base layer with monochrome profile for auxiliary layer
Open Issues:
- Different chroma subsampling between layers
- Different encoding configurations
- Spatial resolution differences
- Bit depth variations
This solution uses two independent HEVC bitstreams:
1. First bitstream: Video content
2. Second bitstream: Alpha plane sequence
Alpha Plane Signalling:
- Alpha plane carried as a single-layer HEVC bitstream
- Current HEVC specification lacks explicit signalling for alpha plane sequences
- Proposed solution: Use specific code points in VUI information
- Reference to potential CICP extension [x2] for signalling via colour_primaries parameter in VUI
VUI Parameters:
- Signalling through colour_description_present_flag and related parameters
- colour_primaries, transfer_characteristics, and matrix_coeffs fields in VUI
Since bitstreams are independent:
- Video content bitstream: Any HEVC profile
- Alpha plane bitstream:
- Monochrome profiles (Monochrome, Monochrome 10, Monochrome 12, Monochrome 16)
- 4:2:0 profiles
Both solutions (#5.1 and #5.2) have evaluation sections marked as "For further study", indicating:
- Performance evaluation pending
- Profile compatibility analysis needed
- Implementation considerations to be determined