JVET-AM0327 AHG9: On GFV SEI [S. McCarthy, P. Yin, G. J. Sullivan (Dolby)] [late]

Chaired by S. Deshpande on 30 June 2025 during 16:40-17:10

It is asserted that the clarity of the current draft of the generative face video (GFV) SEI messages could be improved, particularly with respect to fusion pictures and chroma key information.

Version 2 of this contribution incorporates additional editorial aspects, additional technical aspects, including the addition of a syntax element, and corresponding revisions to the attached specification text.

Editorial aspects:

• Aspect 1: Reword the introduction to clarify the definitions of base picture, fusion picture, driving picture, and chroma key information
• Aspect 2: Clarify the persistence of syntax elements specified for base pictures.
• Aspect 3: Rename the syntax element gfv_drive_pic_fusion_flag to gfv_fusion_pic_flag and simplify the corresponding semantics
• Aspect 4: Simplify the semantics for gfv_chroma_key_info_present_flag
• Aspect 5: Simplify and clarify Note 3 pertaining to the use of chroma key information for alpha blending
• Aspect 6: Clarify the persistence of fusion pictures
• Aspect 7: Rename the variables inputDriveY, inputDriveCr, and inputDriveCb to inputFusionY, inputFusionCr, and inputFusionCb, respectively, to clarify that these variables correspond to a fusion picture.
• Aspect 8: minor improvements to the specification text
• Aspect 9: Correct missing brackets and tabs in the syntax table.

Technical aspects:

• Aspect 1: Replace the syntax elements gfv_chroma_key_thr_present_flag[ i ] and gfv_chroma_key_thr_value[ i ] and associated semantics with syntax elements gfv_chroma_key_thr_lower and gfv_chroma_key_thr_upper_delta_minus1 and associated semantics as proposed in JVET-AM0091.
• Aspect 2: Add missing aspects of the process used to generate a video picture when gfv_chroma_key_info_present_flag is equal to 1
• Aspect 3: Added several constraints as proposed in JVET-AM0091.
• Aspect 4: Add syntax element gfv_base_pic_no_display_flag to enable a base picture to not be displayed when chroma key information is used for background replacement, for example.

It was commented that the proposed updates completely remove alpha blending.

V3 attachment was discussed.

Regarding proposed NOTE 2, it was asked which entity determines the usage of chroma keying as per the example.

There are some other technical change which may not be summarized above.

Also in v3 syntax table an opening brace was unintentionally removed.

Due the the lateness of the document more time was requested for study.

It was suggested that some offline activity should be considered by the proponents of this document and JVET-AM0091 authors.

Discussed again 1 July 2025 chaired by S. Deshpande during 11:55-12:10. Further discussion requested. See notes under JVET-AM0334.