[FFmpeg-user] Intel Transcoding: Vaapi or QSV

[Wang, Fei W]

On Wed, 2024-10-23 at 19:45 +0000, Shane Warren wrote:
> I decided to start a new thread since I have done a lot of testing
> and patching on qsv and vaapi transcoding since last week.
> 
> First, I decided to try to use QSV decoding and QSV encoding, but I
> noticed a53 captions were being stripped out, and I narrowed this
> down to the qsv decoders not passing the a53 captions on. I noticed
> there was a patch for SEI parsing for QSV decoders that was never
> merged into mainline ffmpeg. The patchset can be seen here:
> https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=&submitter=&state=&q=+Implement+SEI+parsing+for+QSV+decoders&archive=&delegate=
>  I applied that patchset up to v6 of the patch. I had to fix a lot of
> API changes from that older version up to my mostly recent version
> but after that patch, QSV decode -> QSV encode passed a53 captions
> and they looked correct in my extensive testing (at least for h264).
> 
> I'm trying to replace our use of nvidia cards and replace them with
> intel cards for transcoding. We make use of overlays, so I was trying
> to use overlay_qsv to allow: h264_qsv -> vpp_qsv=deinterlace,scale ->
> overlay_qsv but a53 captions were getting slightly garbled. I then
> tried a lot of combinations and a53 captions get garbled in all
> these:
> 
> 1. QSV decode -> vpp_qsv -> overlay_qsv -> h264_qsv = bad closed
> captions
> 2. QSV decode -> overlay_qsv -> h264_qsv = bad closed captions
> 3. Software decode -> overlay_qsv -> h264_qsv = bad closed captions
> 4. Software decode -> overlay -> h264_qsv = bad closed captions

Could you share your patch/clip/cmdline to me? I can help to check it.

Thanks
Fei

> 
> I then decided apparently h264_qsv can mess up captions itself, but
> strangely not if using qsv decoding.
> 
> I then settled on: vaapi_h264 -> deinterlace_vaapi -> scale_vaapi ->
> overaly_vaapi and a53 captions worked great and cpu usage (5-8%) was
> the lowest of any overlay I've seen, which means it's almost entirely
> in the gpu.
> 
> Now I'm wondering if I should go back to using vaapi decoding and
> encoding for everything, I had started out this project wanting to
> use qsv since it in theory was the newest and had more features.
> 
> Are there any downsides to using vaapi over qsv? I just want
> something that works and produces good quality transcoding.
> 
> Thanks,
> Shane Warren
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