If you browse to "www.dolby.com", you will find a lot of useful information on Dolby Digital, and you will be surprised to know that when the theaters received a Dolby Digital 5.1 movies, the sound is stored on the film sprockets, simply because there is no location for them. And that's 35MM!!!

Image the 0.5 inch wide VHS tape. There would be no room for them either, in analog or digital...