Подключить внешнюю аудиодорожку к фильму

Video play external audio track

(SMPlayer/MPlayer звук бывает рассинхронизирован)

vlc movie.avi --input-slave sound.ac3

Alternatively in the Qt4 (normal) interface go to:
Media >> Advanced Open File...

Select you video file. Tick "Show more options" then "Play another media synchronously..." and select the *.ac3 file.

Then when playing the video go to "Audio >> Audio Track >> Track 2" to select the second (or whichever it is) audio track.