Document size of mp4 with looping gif and song track

Hi there,

I'm creating an mp4, where the video itself only loops around 6 seconds, but the music track is 3 minutes.

What is the best way to keep the size down of the file?

At the moment, I am coping all layers and spreading them out over 3 minutes, but 30% of them are moving, and the rest static layers - think of a comic page, where some parts of the page will move, but most don't.

Is there anything smarter I can do with the layers rather than spread them out over 3 mins? Some of them have opactiy and movement changes, and these when duplicated really add to the file size.