In French, when you have a mixed gender situation, the default is masculine. If both the films and the music are international, then international must be masculine plural. Alternately, you could make your life easy, and just call the festival itself "international."
I think you're right, cropje_jnr.
Here the link is between "musique" (fem. sg) and "internationale" (fem. sg)
So, you can understand it like : "festival du film" et "festival de la musique internationale"... which looks a bit weird !
I assume there is a mistake in the writing and we've better understand :
"Festival de la musique et du film internationaux".
"film" beeing a masculine word sounds better near "internationaux" than "musique".
Actually, I think Garou22 is asking how to write International Film and Music Festival in French.
As I understood it, both the "film" and the "music" are international... hence the question about what ending is required for international(e)/aux to make proper agreement when one noun is masculine and the other is feminine.
Assuming I've understood the question correctly, then (as I suggested in post #2) "internationaux" is the required form, because we need masculine plural. I like itka's solution: