I had a somewhat similar issue. VLC was attempting to play videos but in a very very 'slow-motion' fashion (like 1 frame / 15 sec).
Problem was some stray processes still running from earlier playback attempts.
1) exit out of VLC and other video/audio players.
2) use 'ps ax' to review processes and identify any sound/video related ones.
3) use 'kill xxxx' to end related process #s.
4) try vlc again
5) optionally reboot and see if problem is reproducible.