In Russian does this mean "your" in the sense or ownership (do you own the rights, I suppose) or does it mean 'the film that you star in' ?
In English both of these would be phrased "your film/ play/ etc."
In Russian, it can mean both too.
I dont understand why i write a question is this your film and i get an error
What is the difference between это and этот? And are they used for both neutral and masculine in the nominative case?
A good explanation is here: https://www.duolingo.com/comment/11536858
Why not vashe
"Ваше" is neuter gender. "Ваш" should be accepted.
Is the gender of "your" in sentences like this determined by the gender of the noun or the person being addressed?
For this purpose think of "your" as an adjective, modifying the next word. It must agree in grammatical gender with that word.
Фильм is masculine. Why use зто instead of зтот?
Because "это" refers to "it", which in Russian is omitted but still has a sort of implied presence. Such "it" is always in the neuter gender.