No, I haven't. I was just passing this part of the forum and saw the thread title and felt like having a look.
Your post made me remember seeing this [
http://hacks.mozilla.org/2011/06/jsm...t-mp3-decoder/], and I think it's the only pure JS solution for what you're trying to achieve.
As for documentation etc, it seems you're on your own there. (I'll assume that any documentation for libmad could be of help, as jsmad is a port of it.)
But yeah, it was just a passing "oh this could help!".