[FFmpeg-user] Problems with nvdec/cuvid

[Boris Petrov]

Hi all,

I have a few questions/issues with nVidia's hardware acceleration of
ffmpeg. I originally posted them as an issue in the bugtracker:

https://trac.ffmpeg.org/ticket/7537

I'll copy and paste them here also for reference:

Why are there two separate implementations of nvidia hardware
acceleration? As far as I understand nvdec is simply a rebranding of
cuvid. Yet in FFmpeg they coexist and exhibit different behaviors.

1. Is either of nvdec/cuvid the recommended one to use? Is either one
deprecated?
2. cuvid does not auto-detect the decoder. This works correctly: "ffmpeg
-hwaccel cuvid -c:v h264_cuvid -i ...", and so does "ffmpeg -hwaccel
nvdec -i ...", but this does not: "ffmpeg -hwaccel cuvid -i ..."
3. cuvid is noticably (although not drastically) faster. Maybe around 15-20%
4. "ffmpeg -decoders" displays some cuvid-related things, but nothing
nvdec-related
5. nvdec is not displayed when running "ffmpeg -hwaccels"
6. When using scale_npp with cuvid it can be used with just "-vf
scale_npp=..." whereas nvdec requires "-vf hwupload_cuda,scale_npp=..."

I'm not sure which of those are bugs, which are by design, which are
normal. I'll appreciate any insight on each of them.

Thanks,

Boris Petrov

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