As you already might have noticed, yaydl --sound fails
from time to time when processing youtube videos, i.e. the
resulting file isn't a valid mp3-file, but just raw data. The
reason for this error lies within the file format. Earlier versions
of yaydl always picked the flv version of a video, whereas newer
versions always try to get the higher resolution mp4 files.
Unfortunately, mplayer -dumpaudio doesn't work properly with
these files. Therefore, yaydl from now on uses ffmpeg -vn
-acodec libmp3lame -ab 192k for non-flv videofiles from
youtube. Nevertheless, I still would prefer the usage of mplayer
for this purpose, but I didn't get it work...
So, if you know how to extract the audio track from a mp4-file with
mplayer, just drop me a note.