[FFmpeg-user] Help with extracting audio from MP4

[Moritz Barsnick]

On Thu, Jan 19, 2017 at 17:18:55 +1100, Peter wrote:
> > Maybe you are searching for something like the following?
> > $ ffmpeg -i 16187821_363927127308754_4400528164682465280_n.mp4
> > -acodec copy out.aac
> 
> Thanks, I tried that. The sound is okay.

No, the sound is not "okay", it should be *exactly* as the original.
ffmpeg can't help you make it any "better" than this (unless you want
to apply filters to change the original).

> For mp3 output, I used an example ..
> 
> ffmpeg -i 16187821_363927127308754_4400528164682465280_n.mp4 -codec:a 
> libmp3lame -qscale:a 2 output.mp3
> 
> Not sure if I'm using the correct parametrs though. We require the output to 
> be an mp3 file.

Basically yes. When trancoding, you will always be trading off file
size versus quality, you can't have the best of both. And whether the
quality setting you choose is sufficient depends heavily on your
requirements, your ears, and your input material. "-q:a 2" is "usually"
sufficient though, while ffmpeg's default of 128 kbit/s constant bit
rate may be too low for most needs.

Moritz