[FFmpeg-user] Trying to solve drop in quality

John Harlow johnrharlow at mac.com
Tue Nov 3 23:54:07 EET 2020


I figured it out. Pointing out that it was the GOP set me on the right path


I eliminated -g and changed:
-x264-params "nal-hrd=cbr:scenecut=0:ref=2:cabac=1:force-cfr=1"
to
-x264-params "nal-hrd=cbr:scenecut=0:ref=1:b-pyramid=0:force-cfr=1"


thanks everyone!



On November 3, 2020 at 4:45 PM, Eduardo Alarc├│n <ealarcong at gmail.com> wrote:


El mar., 3 nov. 2020 a las 18:36, John Harlow via ffmpeg-user (<
ffmpeg-user at ffmpeg.org>) escribi├│:


The -g is definitely the quality problem. I tried setting it various to
30*1000/1001, 60*1000/1001 120*1000/1001, 180*1000/1001, 360/1000/1001and
even 15*1000/1001.






Any of those changes show up in mediainfo as:


Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames






I would have thought the interval for the ref frames was either 2 seconds
(60*1000/1001) or 2 per ts segment


which would be (basically) 180*1000/1001.




I'm not sure how to get to Reference Frames 2.


-g is the gop size in frames, integer, not time, if you want a key frame
every 2 seconds you should use -g 60, when using 30fps.
With gop 2, you are getting a keyframe every 2 frames, so basically your
video is a huge collection of jpeg images
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