Hi there
Just a WAG here, but what if you had just a hyperlink that opened the MP4? Sounds like you are trying to play it from inside a topic and something about that is clobbering things.
Or, perhaps use an Inline Frame? Instead of configuring an HTML file as the source, perhaps configure the MP4?
Sorry, no way for me to test as well, as I don't have wealthy lineage and have never had an iPad.
Cheers... Rick