[FFmpeg-devel] [PATCH 3/3] [RFC] avcodec/ffv1: Better rounding for slice positions

[Jerome Martinez]

On 07/10/2023 02:14, Michael Niedermayer wrote:
> This fixes green lines in some odd dimensions with some slice configurations
> like Ticket 5548
>
> This also changes the encoder and whats encoded, and would require an
> update to the specification. This change attempts to limit the change
> to configurations that have missing lines currently.

It changes a lot the count of pixels per slice, and , e.g. with 4:2:2 and 4 slices per direction (16 slices in total), 13 pixel width:
before: 3/3/3/4 for luma, 2/2/2/2 for chroma (so 1 chroma too much)
after: 4/4/2/3 for luma, 2/2/1/2 for chroma

Wouldn't it easier for spec and maths to keep the previous behavior for luma and consider extra chroma as to be not encoded?
Something like 3/3/3/4 for luma, 2/2/2/1 for chroma
Actually maybe not really a change for spec in that case, more making a part more explicit while considering the patch as a bug fix rather than a spec change.

Or did I miss another issue? I'll check more a bit later.