I have an AVI clip with joint-stereo MP3 audio stream, the problem is that there's sound in right channel only, left one is silent. I demuxed that MP3 and now want to losslessly extract right channel from it and mux back so I'll have sound in both speakers. Is there a tool for that? I know it's possible with MP2, so I guess it would be possible with MP3 too...

Audacity

Edit: Eh, it's not lossless! (But it is free!) Better try....

Data Becker mp3 Editor
Mayah Edit Pro
MPEG Audio Scissors

Technically it's not possible, how do you split a JOINT-stereo file?

It's like spiltting a cojoined twins without killing one/all of them!!

well, rutra80's joint stereo stream will be of lr coded frames only, due to the fact that the left channel is silent. if this is the case, then it is possible to demux it into a mono stream, but I don't know any tool for such a task.

It might even be possible if there are M/S frames somehow, since M = L+R and S = L-R, and L is silent, M would be the same as R...

well, it would not be so easy:

What's the purpose of the constant multiplier? Anyhow, it may still be possible - the program could twaddle the gain value for the block the way mp3gain does.

In my first post of this topic I gave a link to the thread about such a tool for MP2, it was developed by S_O (HA member) and is called mp2chext (source included). It can extract one channel of a dual-channel, stereo or joint-stereo MP2 and copy it to a mono or a joint-stereo MP2, losslessly. BeSplit has similar functionality too. That's why I think it would be possible to do something like that for MP3 too.

Hmm, along these lines I have been wondering if it would be possible to change the framerate (playback rate) of an mp3 file without having to transcode. For example, take an mp3 audio track, and speed it up 4% (23976->25000) so that it will match the film sped up to work with a PAL TV system. Having to transcode here really hurts the audio quality, but video can be told to playback at any arbitrary rate without a recompression.