Greasy Fork is available in English.
Auto-pause any HTML5 videos. Will still preload.
Automatically pauses any HTML5 video element encountered (as soon as it find that it's ready to play).
Works both on page load and whenever a new video element is inserted through code.
Preloading will still happen - it will pause the video whenever it finds it's ready to play. This is beneficial if you want to walk away from the video to find it loaded later on, but it also means that it won't save you any bandwidth.