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I've read lots of articles on starting an application with a specific affinity This works as expected and I see the the affinity is showing as expected: start /affinity 3 notepad

However, when I try to do the same with ffmpeg, it sets all cores as active. I can then change the cores manually but that defeats the purpose. What am I missing?

start /affinity 3 ffmpeg -i "title.mp4" -c:v libx265 -vtag hvc1 "Title-HEVC.mp4"
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  • I agree with you that affinity settings should be absolute but ffmpeg is highly tuned to deal with this on it's own. Use the 'threads' command to control it's use of other processors. Know that limiting it's access to procs can also influence the quality of the output (depending on codec). I don't understand why so please don't shoot the messenger.
    – Señor CMasMas
    Commented Feb 28, 2023 at 17:13
  • Thanks! I'll look into the threading. I'd rather not have the degradation in converting. Since it's not stopping me from doing things by really bogging the system down...i'll leave it as it is.
    – Phil.G
    Commented Mar 1, 2023 at 15:51
  • If you know how to program (especially c#), controlling affinity from code is rather simple to do.
    – Señor CMasMas
    Commented Mar 1, 2023 at 16:07
  • Its been a really long time since I've coded. I'll look into it though.
    – Phil.G
    Commented Mar 5, 2023 at 15:22

1 Answer 1

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The issue is more with libx265 than ffmpeg itself. For an example if you use libsvtav1 you can use /start /affinity xxx and it works fine.

What you can do is first limit amount of cores used by libx265 by adding option -x265-params pools= Then when ffmpeg is running, set the right affinity

My complete set of 2 scripts to do that, i use 3 cores and keep core 0 unused to keep the system responsive : pack.bat

@set fname=%*
@set fname=%fname:"=%

@rem define various constants
@set scale1440=-vf "scale=-1:1440:flags=lanczos"
@set scale1080=-vf "scale=-1:1080:flags=lanczos"
@set scale720=-vf "scale=-1:720:flags=lanczos"
@set scale540=-vf "scale=-1:540:flags=lanczos"
@set scale360=-vf "scale=-1:360:flags=lanczos"

@set b10=yuv420p10le
@set b8=yuv420p

@set a_copy=-acodec copy
@set a_aac128=-acodec aac -b:a 128k
@set a_aac160=-acodec aac -b:a 160k

@set svt_params=-svtav1-params tune=0:enable-overlays=1:scd=1:lp=3:film-grain=
@set hevc_params=-x265-params strong-intra-smoothing=0:rect=0:aq-mode=1:pools=3

@rem define output here
@set pix_fmt=%b8%
@set audio=%a_copy%
@set scale=%scale1080%

@set grain=0
@set preset=slow
@set crf=20

@rem some calculations
@set av1=-vcodec libsvtav1 -preset %preset% -crf %crf% %svt_params%%grain%
@set hevc=-vcodec libx265 -preset %preset% -crf %crf% %hevc_params%

@rem pick encoder here
@set video=%hevc%

%ComSpec% /c start /b "ffmpeg fix" powershell.exe .\fix_affinity.ps1

%ComSpec% /c start "title" /b /Low /wait /Affinity E /d "." ffmpeg.exe -n -i "%fname%" %scale% %audio% %video% -pix_fmt %pix_fmt% "%fname%_p%preset%c%crf%g%grain%_%pix_fmt%.mkv"

and fix_affinity.ps1

start-sleep -seconds 5
$ffmpeg_process = get-process ffmpeg
$ffmpeg_process.processoraffinity=14
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