I don't think I would class films such as "Help" and "Summer Holiday", where all the songs are performed by the same people, as musicals. ie, any of the films issued by pop groups are just films containing music and not musicals.
Tiggs - //Most musicals have song written specifically for the film.//
Although there has been a habit of adapting an specific artist's back catalogue to build a story around, such as Mamma Mia, We Will Rock You, Our House etc.
tiggs, older musicals were often collections of back numbers. Singin' in the Rain wasn't written for Singin' in the Rain, it was in a film 20 years before.
You are right IMO otherwise musical becomes too broad a term, and would include the Elvis Presley and Beatles vehicles for example. Aren't those Jukebox Musicals?
Elvis sings in his films. The Beatles sing live at the end of Let it Be, but the rest of their films, though they're not necessarily mouthing the words, they're in the accompanying image, like many music videos. It's not like the music is just soundtrack from someone else as in Easy Rider, for instance.