[FFmpeg-user] Minimize CPU use with QuickSync?

[Li, Zhong]

> -----Original Message-----
> From: ffmpeg-user [mailto:ffmpeg-user-bounces at ffmpeg.org] On Behalf Of
> Jason Coleman
> Sent: Friday, July 6, 2018 11:33 PM
> To: FFmpeg user questions <ffmpeg-user at ffmpeg.org>
> Subject: Re: [FFmpeg-user] Minimize CPU use with QuickSync?
> 
> I didn't have a specific reason to utilize the software decoder. I didn't realize
> I still was. In retrospect, it makes sense that I would have to specify the
> decoder as well, I'd chalk it up to lack of familiarity with how ffmpeg works. I
> made the changes you suggested, which really makes for a much simpler
> looking command, so that's nice. I had built my command based on
> information I scraped together doing a lot of reading of out-dated posts and
> a lot of searching online.
> 
> 
> In any event, I'm still seeing around 20% CPU usage, but I'm not sure from
> where, but I'm really pleased with the change because on the GPU end, I'm
> seeing around 75% utilization now, and in particular where my transcode was
> running around 4x before, it's running around 16x now, so that's fantastic.
> I'm not 100% sure that the CPU usage isn't just from more network overhead
> from everything running so much faster.

Glad to see it works. There are still some tasks are done by CPU
(e.g, video muxer, demuxer, audio copy, video frame header parser for qsv decoder, video frame header generated in qsv encoder and so on).

> 
> I've also run into the occasional file that fails to transcode because it looks
> like something in the stream is breaking the QS decoder, actually. Some
> entries on the ffmpeg bug list suggest it's a problem in how QuickSync is
> handling some frame types? Anyway, different problem, but I'm keeping my
> original line around as well, so that for the files I have problems with, I can
> switch back to the software decoder.

If you find any clips can't be decoded by QSV decoder, please file a bug on https://trac.ffmpeg.org/ 

> 
> Thank you, that was very helpful!
> 
> 
> 
> 
> ________________________________
> From: ffmpeg-user <ffmpeg-user-bounces at ffmpeg.org> on behalf of Li,
> Zhong <zhong.li at intel.com>
> Sent: Thursday, July 5, 2018 10:16 AM
> To: FFmpeg user questions
> Subject: Re: [FFmpeg-user] Minimize CPU use with QuickSync?
> 
> > -----Original Message-----
> > From: ffmpeg-user [mailto:ffmpeg-user-bounces at ffmpeg.org] On Behalf
> Of
> > Jason Coleman
> > Sent: Friday, June 29, 2018 4:49 AM
> > To: ffmpeg-user at ffmpeg.org
> > Subject: [FFmpeg-user] Minimize CPU use with QuickSync?
> >
> > Hello,
> >
> >
> > I recently picked up a computer with a Kaby Lake processesor, and I'm
> > trying to setup ffmpeg transcodes to minimize impact to the CPU and
> > maximize use of QuickSync during transcodes. I am going by indirect
> > indicators (CPU use and GPU use, as indicated in the Windows 10 task
> > manager) + what ffmpeg output says. I thought I had the entire
> > pipeline (decode/scale-resize/encode) being performed by Quicksync,
> > but I'm still getting a lot of CPU use, call it 70-90%.
> 
> This is not an "entire" Quciksync pipeline as your command line below.
> You are using a software decoder output to system memory, then upload as
> qsv surface and use qsv to do scaling and encoding.
> So high CPU usage is normal IMHO.
> 
> Maybe my expectations are out of line and I need to adjust those?
> > Am I missing anything that would cause operations to happen on the CPU
> > instead? I'm currently using a zeranoe 64 bit build, on Win10 home,
> > with the current Intel drivers. So this is an example encoding line, I
> > don't have an output from ffmpeg in front of me, apologies, I can put one
> up later:
> >
> >
> > C:\ffmpeg\ffmpeg.exe -hwaccel qsv -init_hw_device
> > qsv=qsv:MFX_IMPL_hw_any -filter_hw_device qsv -i "testvid.mp4" -vf
> > "format=nv12,hwupload=extra_hw_frames=100,scale_qsv=640:360" -b:v
> 800k
> > -c:v h264_qsv -c:a copy -y "testoutput.mp4"
> 
> Is there any reason to use software decoder? If no, you can try to add "-c:v
> h264_qsv" to specify qsv decoder (then "-init_hw_device
> qsv=qsv:MFX_IMPL_hw_any -filter_hw_device qsv" is not necessary, and
> also remove "hwupload"):
> C:\ffmpeg\ffmpeg.exe -hwaccel qsv -c:v h264_qsv -i "testvid.mp4" -vf
> "scale_qsv=640:360" -b:v 800k -c:v h264_qsv -c:a copy -y "testoutput.mp4"
> 
> <I haven't set up QSV on windows yet. If this doesn't work, please let me
> know>
> 
> >
> > Thank you!
> >
> > Jason
> 
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