Music is an important element in almost all films, so sorting out the subtle differences between music-related genres becomes something of a semantic argument. For a film to fall into the music genre, music must be a primary focus of the movie. Whether that focus involves actual performance of the music or a broader, more conceptual musical theme is less of a crucial question.
Musicals, in which the music and songs in the film play a role in the movie's storytelling, can fit into the music genre, but the music doesn't necessarily have to be essentially a character in the film the way it is in, for example, "The Sound of Music" or "High School Musical."
The musical biopic is an example of a subgenre in which the actual performance of the music isn't necessarily the point. Music biographies may, in fact, include extensive performance sequences, but the life stories of the performers as told through dialogue and non-musical scenes is at least as important as the songs.
Sometimes, however, there's little point to a music movie beyond the performance of the music itself. Concert and performance films have long been favorites of fans of pop and rock stars ranging from Led Zeppelin to One Direction.