Excellent art-house film in projector (7)
I believe the answer is:
acetate
'film in projector' is the definition.
'acetate' can be an answer for 'film' (type of material). I am unsure of the 'in projector' bit.
'excellent art-house' is the wordplay.
'excellent' becomes 'ace' (ace can informally mean very good).
'art house' becomes 'tate' (I can't explain this - if you can you should give a lot more credence to this answer).
'ace'+'tate'='ACETATE'
Can you help me to learn more?
(Other definitions for acetate that I've seen before include "Artificial textile fibre" , "It once covered records" , "Material in old record" , "(Chemical used in production of) clear film" , "Recording" .)