Naked Afternoon" (1976)
Perhaps the first "meta" porn movie, "Naked Afternoon" stars the beautiful and innocent-looking Abigail Clayton as an aspiring actress who ends up making adult films. It earns its place on the list of the top 10 best adult movies of all time due to her enthusiastic and realistic performance.
Blue Movie (1995)
A young reporter is given the assignment of covering an adult video-shoot, hoping to dig up some dirt on its mysterious transvestite director. A director who also happens to be her favourite. Stars Jenna Jameson.
I do know there was another 70s movie where the plot was a camera girl or assistant who takes over the lead role during the filming of an adult movie....the title just escapes me.
I also remember Ashlyn Gere made a movie along those line...
[Link]