MP4 to MP3 (Video+Audio -> Audio)

[Kapitano]

On 8/25/2013 16:48 PM, Shevek wrote:
> After download, you can use ffmpeg to extract the audio
>
> ffmpeg -i file.mp4 -vn -acodec copy file.aac

Can ffmpeg identify which audio and video codecs are used in a given 
file? Is there a way to 'ask' it whether an MP4 has sound encoded in 
aac. mp3, speex etc?

It just seems awkward that I have to play the video in VLC to find out 
its format, just to find the file extension I should give the output 
file when I use ffmpeg to extract it.