Do you mean could you have an mp4 video background that had music with text over the top?
Unfortunately, you currently can't output audio from the background content, however, it is something that we are going to have a look at in the near future as it has been requested. We want to make sure we get it right!
Its a bit long winded but I use a Mac that has both Mac & Windows 10 - I create a Keynote slide in Mac with the music track imported (plus any background I want) and then export it as a video. I then transfer this to Freeworship and bring in as a video and it works fine. I realise that not everyone could do this!