[FFmpeg-user] Confusion about quality parameters

Ulf Zibis Ulf.Zibis at gmx.de
Wed Jun 26 13:51:08 EEST 2019

Am 26.06.19 um 09:58 schrieb Moritz Barsnick:
> This has nothing to do with the dev branch, only with your particular
> build. It uses different codecs, and these behave totally differently -
> both by nature, and by default settings.

> The mpeg4 encoder encodes differently than the x264 encoder. You *may*
> find settings where both achieve the same quality at the same video
> bitrate, but that would take a lot of experimenting. (Note: encoding is
> mostly a trade-off between bitrate/stream size, quality, and encoding
> time. And the actual codec used.) Usually, an MPEG4 stream at approx.
> the same quality as an H.264 stream will use significantly more
> size/bandwith/bitrate. (Very generally speaking.)
> That your mpeg4 video turned out much smaller is due to the fact that
> ffmpeg's mpeg4 setting defaults to "200kbit/s CBR with best effort",
> regardless of resolution. ffmpeg's x264 default is "CRF 23, VBR", which
> tends to (well, almost always will) result in much higher quality at
> sane resolutions, e.g. 480p upwards.
Much thanks, as this is more than I wanted to know.
Now I fully understand :-)

>> Please have a thought on my question 1.)
>> Where in the documentation I find, which quality is used by default and
>> how to change it?
>> In other words, wouldn't it make sense to add this, if this information
>> is missing?
> IMHO it would make sense, especially as "ffmpeg -h encoder=blafoo"
> cannot tell you.

Thanks! Here my report: https://trac.ffmpeg.org/ticket/7973#ticket


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