i heard about the issue of missing audio (no sound)
when playing video-files containing mp4a-audio
and was surprised to hear
that some users recommend to use another player
or install additional codecs or plug-ins (also in other forums).
there is a small failure within vlc (fe 1.00-1.05)
that i wanted to tell you about:
if in preferences "inputs & codecs" you choose
"use system codecs" and save this setting,
the above error will occur, if the system-codec is
not able to play mp4a-sound, which obviously
sometimes is the case.
if you uncheck this setting again and save that,
surprisingly, no change to the better will occur,
i lovingly call that the "obama-behaviour"
hoewever, you can clear the situation by
"re-setting the preferences" on the lower end
of the page.
vlc will then play the audio again!
hoping to have been of help, dw.