[FFmpeg-user] Why _COPYing_ a variable encoded audio (AAC) channel will produce a variably encoded one?

[Carl Eugen Hoyos]

2018-02-28 13:40 GMT+01:00 Sophoklis Goumas <olspookishmagus at gmail.com>:

> I have a .3gp file containing a video and an audio channel.
>
> I'm trying to get the audio channel in a separate m4a file but when I issue:
> ffmpeg -i foo.3gp -vn -c:a copy foo.m4a

Complete, uncut console output missing.

> I get a constantly encoded AAC audio channel
> while the original was a variably encoded one.

Why is that an issue?

Carl Eugen