I have yet to see a convincing mime of instrument playing but Forest Whitaker's Sax. synch. was terrible. His acting of a drink and drug dependant musician was as unconvincing and uninteresting as you could possibly imagine for such an otherwise talented actor.
A film biography of a drug addict is a difficult undertaking, it hard to think of how it could have been done better but the result is underwhelming. The jazz tracks are great and a beautiful thing to listen to, it's just the rest that fails.
I have read that Clint is a big 50's jazz fan. If you are too then this is probably a good film for you. I am only averagely interested in club jazz and so this film, even with the massive talent of Forest Whitaker, is pedestrian.