Bob has written a short piece of music and realized that it brilliantly fits certain sequences from a certain famous, copyrighted movie. He cuts essentially a music video from those sequences which appears quite fun and entertaining.
On the one hand, Bob's derivative work may be regarded as:
- joke/prank on the particular scenes from the movie that Bob used: his music may change how the scenes are perceived (e.g. make them look fun where they did not), or make them look much more fun/amusing than they were;
- tribute to the movie (which is not just famous but actually cult);
Also, there may be actual dancing and the actors' movements may look as if they indeed danced to Bob's music (rather than to what was used in the movie).
Overall, it would be hard to imagine a way in which Bob's clip would cause any detriment to the movie's copyright holders. In fact, if it causes any effect on the movie at all that would be a spike in its DVD/Bluray/streaming sales.
But on the other hand, the clip could be seen as employing the fame of the movie to promote the piece of music Bob has written. Although Bob will not be monetizing the clip itself, he could by all means benefit from selling the music only through other channels.
Could there be any defenses for Bob against copyright infringement (e.g. fair use) if he posts the clip on Youtube but otherwise does not aim to directly make any money out of it? What tests would courts apply to determine if these defenses stand?
(Closely related but different: Large YouTuber: Copyright Lawsuit vs Fair Use)