Hi,
I think that you should first clearly define your needs. You are talking about some (parts of) solutions that seem to correspond to very different needs, so I don't know exactly what you want to do...
Ideally it would involve creating an ibay, dropping in some scripts and mp4 files and creating user accounts.
If this is what you want, where is the problem ? Just do it

Seems that you just want some web page with a video viewer, as in Youtube ? It's easy to do with basic html. Think also that maybe you don't need a web viewer, as people could just click on a link and they will have a dialog box asking if they want to save the video on their disk or see it in their video player.
But you talk also about users accounts. It's possible to do that with ibays properties, but maybe you don't want to have many ibays. If so, you'll have to do that with some PHP scripts. Not difficult, and you have a lot of samples and tutos on the web.
And if you don't want to do that yourself, there is surely some GPL-licenced solutions ready to use. Galleryserverpro seems to be a ready to use solution, but not a free (as a free speach, not as a free beer) one (I never used it and even not know what it is, just had a very quick look at their home page). Just remember that it's
necessary and
sufficient that it covers your needs.
Don't take things the bad way : the good way is to list your needs, clearly define what you want (including the accessibility, the presentation etc.), and then only look for the possible solutions. The bad way is to choose a solution, and try to adapt it to your needs.
[you say mp4, but...]
It's always better to use open standards, even if they are less known. Not only it's better for accessibility, but it's often easier to find GPL-licenced solutions using open formats.
[/you say mp4, but...]
As says RequestedDeletion, you could be interrested by owncloud. Depends on your needs...