Xlights 3.x allowed ogg,wav,mo3 and MP4 as the sound track. Xlights 4.x only allows MP3. This happened with the complete rewrite in 4.x to allow a waveform to be drawn, click in waveform to play ,etc.
It has not been high on our list to fix since audacity allows easy conversion. We have lots of other things on the todo list that will take us into next year
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