JVET-AP0136 AHG9: Fixes to subpicture signing for digitally signed content SEI messages [M. Pettersson, R. Sjöberg, M. Damghanian, S. Harribey (Ericsson)]

This contribution proposes the following fixes to digitally signed content (DSC) SEI messages for subpicture/region-based signing in the VSEI TuC:

1. Remove dsci_num_separate_picture_segments_minus1 from the syntax table. This syntax element appears not to be used.
2. Change dsci_picture_segment_mode_flag to dscs_picture_segment_mode_flag in the semantics for the digitally signed content selection (DSCS) SEI message.
3. Change dscs_picture_segment_id[ i ][ j ] to dsci_picture_segment_id[ i ][ j ] in the semantics for the digitally signed content initialization (DSCI) SEI message.
4. Infer the values of dsci_picture_segment_mode_flag and dscs_picture_segment_mode_flag to be equal to 0 when not present.
5. Set the constraints for the value range of dsci_num_picture_segments_minus1[ i ] and dsci_picture_segment_id[ i ][ j ] only when they are present. Alternatively, infer these values to be equal to 0 when not present.
6. Change from past tense to present tense in the semantics of dscs_skip_flag by changing “indicated” to “indicates”.

The group agreed to all six items.

JVET-AP0136 AHG9: Fixes to subpicture signing for digitally signed content SEI messages