[FFmpeg-user] Confusion about quality parameters

[Carl Eugen Hoyos]

Am Di., 25. Juni 2019 um 14:15 Uhr schrieb Ulf Zibis <Ulf.Zibis at gmx.de>:

> my input is a 1.5 minute mp4 video with 19.5 MB
>
> When I use (with build from dev):
>     ./ffmpeg in.mp4 -c:a copy out.mp4

You do not specify an encoder here, mp4 defaults to x264.

>     ffmpeg version N-93873-g6276b4db97 Copyright (c) 2000-2019
> the FFmpeg developers
>       built with gcc 7 (Ubuntu 7.4.0-1ubuntu1~18.04)
> in the output lines e.g.
>    frame=   51 fps=0.0 q=31.0 size=     256kB time=00:00:02.05
> bitrate=1018.9kbits/
> I see q=31.0. (the output file is only 5.9 MB)
> In the first view this seems to correspond to:
>     2 Codec Options

>     qmax integer (encoding,video)
>         Set max video quantizer scale (VBR). Must be included
> between -1 and 1024, default value is 31.

This option only applies to (some) internal encoders, not x264.

Carl Eugen