From: "Monty Montgomery"
<xiphmont(a)gmail.com>
The audio track in a youtube file *is* Vorbis (in an mkv container).
Don't have ffmpeg reencode it, just de/remux it.
... I don't have a command like handy though :-| Can't be too hard
with gst-launch though.
ffmpeg ... -acodec copy ...
should do the trick (so remove all output settings for the audio track)