It remembers your preferred volume, though that feature isn't very discoverable. You could set it to zero and all videos would start muted. Ideas on making that more discoverable?
Perhaps have a separate url for "proper" video? Or an option to turn off the mute by default (as opposed to having it turn off automatically the first time you unmute a video.)
Or just require videos with sound to click to play. It's the combination of sound and autoplay that is annoying.
1. Start off muted. 2. If the user views a video that has sound and is muted, put some small verbiage under the video saying it's muted.