I don’t really see a reason to have a composite key in your subtitles table. Unless of course, you want to have something fancy like “The first subtitle line of movie 1023 is to be found at (1023, 1)”. It is debatable if that is really a good reason, though.
If you insist on using composite primary keys: Outside of linking tables, gii isn’t handling them too well. See giix for that.
Composite keys can be handled but imho should be avoided, if you can modify the database schema. That makes developing client apps much easier.
And normally composite PKs are ONLY used in join tables for MANY_MANY relations, which are not directly referenced in the application. If they are, the relation should be split into two HAS_MANY and BELONGS_TO relations and an id column should be added to the join table.