This has nothing to do with the MP4 files. Player controls are handled by the program, in this case PowerPoint. And MP4 doesn't support transparency, anyway, so this approach is wrong on all accounts. If you realyl need transparency and it needs to work in PP, your only option would be to use a suitable AVI CoDec. Otherwise simply include the proper background in the animation. I would strongly suggest you read up on this stuff and by that I don't just mean Adobe. Your lack of knowledge of PowerPoint seems just as severe (no offense).
Well....thank you for the information, sir.
I didn't realize my question highlighted my "severe lack of knowledge". You comment, in fact, did greatly offend me.
I misjudged the safety of asking questions here.
I won't make that mistake again.
You can't get a transparent background in an MP4, but you can try to match the background color of your PowerPoint project! MP4's compression is pretty famous for messing with color accuracy though, but it's worth a shot!