[FFmpeg-devel] [PATCH] avcodec/h264_slice: compute and export film grain seed

[James Almer]

On 8/12/2021 9:08 AM, Niklas Haas wrote:
> On Wed, 04 Aug 2021 19:00:48 +0200 Niklas Haas <ffmpeg at haasn.xyz> wrote:
>> +    if ((sd = av_frame_get_side_data(cur->f, AV_FRAME_DATA_FILM_GRAIN_PARAMS))) {
>> +        AVFilmGrainParams *fgp = (AVFilmGrainParams *) sd->data;
>> +        fgp->seed = cur->poc + h->poc_offset << 5;
>> +    }
> 
> The order on this is wrong, it must be be (h->poc_offset << 5).
> 
> I'll submit a new patch when I can verify that I actually get the
> correct output. I'm not sure if my grain synthesis code is bugged or if
> the seed value is just wrong. (The grain I get looks visually similar,
> but completely different)

Did you try with only one frame thread? I recall Derek noticed that 
trying to attach something (like SEI derived values) to a frame long 
after slice contexts are initialized was not working for frame threaded 
scenarios.
If the output is bitexact regardless of amount of threads, it should be 
fine.