Fade (out) Audio in avconv

Question

I'm trying to cut and fade out the last 4 seconds of a mp3 file:

avconv -i SPEX_pilot_02.mp3 -t 0:0:25 -filter:a fade=t=out:st=21:d=4 preteach-words.mp3

There is no error, but there is no fade out effect applied. ):

My version is avconv 0.8.10-6:0.8.10-0ubuntu0.13.10.1

avconv -filters | grep fade gives me

fade             Fade in/out input video

On the Official LibAV documentation the fade filter is only listed in the video filters section and is using frames as parameters.

Answer 1

avconv can do a video fade out, but doesn't appear to fade out audio. I'd recommend you use sox instead. The syntax is:

sox song.mp3 faded.mp3 fade 5 240 8

In this example, song.mp3 is your source, faded.mp3 is the output, 5 is the fade-in time (you can leave that at zero if you only need a fade out), 240 is the length of the audio, and 8 is the fade-out time. So, for your specific example, you would use:

sox SPEX_pilot_02.mp3 preteach-words.mp3 fade 0 25 4

Source: http://archive09.linux.com/feature/57897