I created a nice movie layout using only the Node editor. I added an mp3 audio file via the video sequence editor. Selected Both compositing and sequence in post processing under render properties and clicked the animation button and got a nice mp4 movie.
When I replace my mp3 file with a movie clip (containing both audio and video) in the video sequence editor and hide the movie by clicking the eye and set opacity to zero + moving the clip outside the start and end frame interval, I get an undesired result. The generated output movie does not contain any video, only audio.