So, let's say you have a bunch of DivX 5.0-encoded AVI files of a live concert. And you really like these files, and have them playing all of the time -- not so much so that you can watch, but so that you can listen to the music. Well, at that point, it sure would be a lot more convienant if these files were mp3 files, instead of DivX video files.

And let's further suppose that this very situation happened to a certain someone who owns this blog, and that he decided to hack his way out of it. This is what you might do:

ffmpeg -acodec copy -i Denali02-Blackcat-Apr2003.avi 02.mp3 -map 0.1:0

The 'ffmpeg' command is an open source project for recording, encoding, and slicing video and audio files. I had a vague notion of this program (I remembered installing the FreeBSD port as a dependency for something more interesting, like VLC I think). But a little googling brought be back to this program, and the above command line (applied to each of my video files) was exactly what I wanted.

I know that I could have used some program like "Audio Hijack" in order to get the raw audio, but then I would have had to re-compress it into mp3 format, and that would have been too lossy for my tastes. Instead, I wanted to simply demux the video files, stripping off the audio stream and saving it to a separate file. Which is exactly what the "-acode copy" flag did -- it specified that the audio codec to be used in the transcode should be a straight copy. The other bit of magic is the "-map" flag, which performs a one-to-one mapping from a stream in the input file to a stream in the output file. VLC said that the audio stream was stream #1, but according to ffmpeg, it was stream #0.1. Go figure.

But anyway, now I have my mp3 files, and they are in iTunes, and based on the lyrics, I am figuring out which song is which. Awesome!

-Andy.