JVET-AL0086 AHG9/AHG13: On Spatial Resolution for the Film Grain Characteristics (FGC) SEI message [J. Samuelsson-Allendes, S. Deshpande (Sharp)]
This contribution relates to the Film Grain Characteristics (FGC) SEI message. It is proposed to add signalling of width and height as extension of the FGC SEI message. It is asserted that this signalling allows for encoders and decoders to properly handle the combination of resolution changes and Film Grain Synthesis (FGS). The proposed solution is claimed to have the following advantages:
- It is backwards compatible in the sense that no change is expected from existing encoders and decoders with support for the FGC SEI message.
- It does not reinterpret/overload existing syntax elements with properties they were not intended for.
- It applies not only to VVC and RPR, but also to general Adaptive Bit Rate (ABR) streaming with VVC, HEVC, and AVC.
The same change is proposed for VSEI and HEVC (but not for AVC). In the second version of this contribution the proposed change for AVC is withdrawn since the extension mechanism in the SEI message syntax table does not exist in AVC. The second version of the proposal also adds setting the variable SeiExtensionBitsPresentFlag equal to 1 in the syntax table.
The proposed solution would not be in conflict with existing implementations, as the new syntax elements could be ignored. The parameters would give the information about the intended resolution that the parameters were generated for in the SEI message itself.
It was asked if it would in principle be possible to have several SEI messages for different resolutions in the same bitstream. It was commented that this could be problematic for existing implementations that would ignore the new parameters, and not know which one to use. It would further cause the problem that those would need to be within a given resolution. It was further commented that additional messages could also be provided by SPO/PON.