Comment 4 for bug 1075497

What I found at this point:
- xingmux tries to compute the number of frames from a sum of their duration. And this is wrong, as I've found several rounding errors in the calculation.
- IMHO it's incredibly easier to just count the frames. I've yet to search if using the duration is really needed.

But! With my test vbr-mp3 files, containing 8700 frames, gstreamer is wrong at 8699, but mp3val's 8701 frames are wrong too.
I think mp3val count the frames including empty ones? The file does have an empty first frame, containing the xing header. I'm not sure about what to do with that, I must check how lame generates its xing header.