The full understanding of my bachelor's thesis requires the reader to watch a movie, how do I deal with that?
I don't think I see a problem here.

If you were writing a literary analysis of Jane Eyre, you wouldn't include the full text of the novel in your paper, and it'd be entirely reasonable to expect the reader to read the novel in order to understand your paper.  I don't see why a film should be any different.  

Your professor can, and should, watch the film, and any others they find necessary in order to make sense of your analysis.  That's not an unreasonable thing to expect, it's just part of their job, like any other background reading they might need to do.  If you can lend them your DVD, or tell them how to otherwise get it, that would be a nice courtesy.

Other readers will have to make out as best they can.  It might be nice to list on your website some ways they could acquire the film (Amazon link, Netflix availability, etc) but again this is more a courtesy than an academic requirement.

But to really cut the knot: Just ask your professor. They are in the best position to advise you, both on the academic standards of your field as to the content of the thesis, and as to what resources would be helpful to them personally in evaluating it.