This is a repeat of my earlier post except this is hopefully clearer and a more precise problem description.
See the diagram attached. Essentially what I want to do seems quite simple but I haven't been able to achieved it yet, the stumbling block being getting an output movie (Save Frames to Movie) with the same number of frames and frame rate of the input movie.
I want to take a QT movie and create another QT movie with the same frame rate and the same audio track. I want to do some image processing on the input movie frames where sometimes the processing may be fast (taking less than 1/fps) but more likely slow (taking more time than 1/fps).