The VideoLAN Forums

Posted: **21 Sep 2016 19:50**

Hi,

few days ago I found weird behavior with FFMpeg. While encoding into h264, if you use constant quality setting and veryfast preset, it takes less time and produces smaller file than with faster preset. I filled a bug (https://trac.ffmpeg.org/ticket/5854), but I didn't realize it was problem of libx264, not FFMpeg, so it got closed.

I have since tested it on VLC with very similar results:

Code: Select all

vlc.exe --no-repeat --no-loop -I dummy newmobcal1920_12mbps.ts --sout=#transcode{vcodec=x264,venc=x264{preset=faster,crf=23}}:standard{access=file,mux=mkv,dst="result-faster.mkv"} vlc://quit
vlc.exe --no-repeat --no-loop -I dummy newmobcal1920_12mbps.ts --sout=#transcode{vcodec=x264,venc=x264{preset=veryfast,crf=23}}:standard{access=file,mux=mkv,dst="result-veryfast.mkv"} vlc://quit

result-faster.mkv has 90.4 MB
result-veryfast.mkv has 76.5 MB

I consider the results very counter-intuitive and I think many people would automatically use preset which takes longer (e. g. faster preset) and expected smaller file size with same quality in return. In reality, they would just waster their CPU time, because the result file is bigger.

Do you think it is worth filling a bug? If yes, where can I post bug for libx264?

Best Regards
Milan

Posted: **23 Sep 2016 10:35**

This can happen, this is normal. It depends on the input.

Posted: **23 Sep 2016 20:35**

I have tried inputs in H.264, MJPEG and MPEG-2 (each completely different video) and with each one there was this problem, so I find it pretty suspicious.
Do you know about video with which faster preset outputs smaller file size than veryfast preset?

Posted: **24 Sep 2016 05:31**

Hi Everyone,
I am looking for a 8K-SDI video test signal generator that outputs SDI and HDMI. It should have all the typical 'old' standard multi color bars, cross hatch SMPTE 259M,SMPTE 292M/SMPTE 424/425M and timer etc.
I have QuestTel 3G-SDI Pattern Generator that can handle HDTV NTSC or PAL and 16:9 formats to 720p and 1080p.
While I have been able to find a myriad of stand alone units, which is fine I am looking for recommendations, or stay away from's.
I also would be interested in a USB option if available for true portability (something I can throw in my laptop case).
Any help would be appreciated!
Thanks all.
Dan

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H.264 encoding - veryfast preset produces smaller file than faster preset

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Re: H.264 encoding - veryfast preset produces smaller file than faster preset