Great, watching a movie to the sound of people munching.
I've watched movies at Alamo Drafthouse with people eating around me multiple times and have never noticed anyone chewing.
I'm pretty sure YouTube doesn't send you an unencrypted stream (anyone know for sure?). I've always assumed you run their EULA-bound, DMCA-protected software in order to decrypt that stream and watch it. Easy enough to save that, of course, but you have to bypass the DRM.
Depending on the quality, but at HD+ for sure, the videos are downloaded as video and audio streams separately from public sources, without any kind of DRM. It's possible to manually grab those files and mux them locally (that's what the player is doing in real time). I used to do that before I found an acceptable local downloader program that handles that for me.
Quark! Quark! Beware the quantum duck!