[FFmpeg-user] FFmpeg and libx264 presets and Constant Rate Factor (CRF)
wsc4 at optusnet.com.au
Mon Aug 9 06:37:22 EEST 2021
>> If I choose a CRF of 20, and I use the "veryslow" preset, the quality
>> still be the same if I choose a CRF of 20 and use the "superfast" preset?
>> The same with this. If I choose a CRF of 10, and I use the "veryslow"
>> preset, the quality will still be the same if I choose a CRF of 10 and
>> the "superfast" preset?
>> The quality will be (very) similar in both cases, it will not be 100%
>> Carl Eugen
> It will not be 100% identical?
> Do you mean the "very slow" compared to the "superfast" at a CRF is not
> 100%? Or, a CRF of 20 compared to a CRF of 10 is not 100%?
> The quality will be (very) similar in both cases, it will not be 100%
I ran a test of a Blu-ray video segment that goes for 2 minutes and 30
seconds and converted down to 1280 x 720 res.
-c:v libx264 -preset (superfast or veryslow) -crf 20
superfast time = 1:10
" bit rate = 6093 kb/s
" bytes = 118 MB
" CRF = 20
veryslow time = 15:37
" bit rate = 4157 kb/s
" bytes = 84 MB
" CRF = 20
I looked at both playing together and I could not see any difference in
quality. Even frame stepping to clear images and both looked the same. I
did notice superfast bframes are 3 and veryslow bframes are 8. This, and
the bit rate comparison, indicates that superfast should have the better
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