It's one thing to advise someone that the market for epub3 books is currently pretty limited; in case they didn't know. However... given that the OP seems perfectly OK with building this epub for personal use—and possible future distribution—and given that ePub3 is a perfectly valid and documented format, why should they have to put up with hearing unrelated reasons for why you don't personally want to have anything to do with ePub3's audio/video features? That's not relevant.
I don't know the answer to the question, but I certainly hope someone who does can help the OP out. Because it appears to be a valid question that deserves a straight answer instead of format-proselytizing.