[FFmpeg-user] Confusion about quality parameters

Ulf Zibis Ulf.Zibis at gmx.de
Tue Jun 25 21:01:49 EEST 2019

Am 25.06.19 um 15:23 schrieb Moritz Barsnick:
> The reason for the size difference is pretty obvious, if you actually
Not to me. With setting q the same value for both builds, i.e. 28.0, the
size and the visual quality is *much different*, even from honoring the
complete output and even libx264 vs. mpeg4.

Question 4.) So why is the default of the dev build set to such bad
quality and why are the q factors such incoherent?

> look at the *complete* output.
> (Which, again - for everyone - is the
> reason we request to see it. ;-))
Obviously you didn't view my post to the end. There it is.

> Your self-compiled binary does not include support for libx264,
> therefore the output format mp4 defaults to the mpeg4 video codec. This
> behaves totally differently to libx264, therefore the sizes (and
> default quality settings, and more perhaps) differ.

This is what I really didn't strike. Thanks for the hint. But I think,
it doesn't answer the above question.

> Otherwise, regarding "-crf" vs "-q" (and everything else): Please see
> what Carl Eugen wrote.

Sorry, I don't see any answer on this in Carl Eugens post.

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?


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