Fast(er) transcoding from aac to mp3.

bat guano batguano999 at
Fri Mar 18 08:52:02 EDT 2011

I sometimes download BBC radio shows to listen on my mp3 player.
It looks like I'm going to have to start transcoding them from aac to mp3.

Using Ubuntu I did some tests to see just how long it takes to transcode these things.

I downloaded a 3-hour show (Steve Wright in the Afternoon*) and calculated the time taken
to convert it using ffmpeg.
This is the command:-
time ffmpeg -i filename.aac -acodec libmp3lame -ab 128k test1.mp3

The result:-
real    20m42.369s
user    17m40.318s
sys    0m56.812s

That's over 20 minutes!
During the test I wasn't running any other heavy programs. I kept checking the System Monitor, it was
always up there at 98%, 99%, 100%. There's nothing wrong with my ffmpeg, it's a new one from git.
Doing the best it can on my Celeron D 2.26GHz computer.

Then I repeated the test using GOGO-no-coda encoder, a turbocharged version of LAME.
It needs wav as input so I piped it through ffmpeg.

I converted the same show using this command:-
time ffmpeg -i filename.aac -f wav - | gogo -b 128 -q 0 stdin test2.mp3

The result:-
real    10m30.195s
user    8m12.411s
sys    0m31.382s

That's about half the time.

If any of you feel like trying GOGO-no-coda it's available in Ubuntu's repo.
Install it like this:- sudo apt-get install gogo
Or download a deb from somewhere.

For Windows users it's available from and other places.

I suppose, if the programmes are talk-shows then it will be OK to reduce the q setting for gogo
and also maybe reduce the bitrate to 96Kbps or 64Kbps. That would speed things up even more.

If any of you have experience using different mp3 encoders it would be good to know how they compare with gogo.

* I didn't listen to the show. For test purposes only. :-)

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