i took an mp4 (frozen), loaded it into audacity, exported out the audio as an mp3.
i then sequenced xlights with the mp3 (we do not recognize mp4's)
after finishing, i send the fseq and the mp4 to the fpp.
When the fpp plays the mp4 i had audio and video and lights perfectly sequenced.
http://nutcracker123.com/nutcracker/releases/Lame_v3.99.3_for_Windows.exe
is the ffmpeg plugin for audacity that lets you open mp4 files in audacity