Greasy Fork is available in English.
Prevents auto-play HTML5 videos in new tabs on any page (not just YouTube) and pauses videos when leave/switch/change the current tab, to prevent any video playing in the background. This auto play blocker is an alternative to Click-to-Play / click to play. On some times like YouTube, click twice to begin first playback — From Dan Moorehead (xeonx1), developer of PowerAccess™ (http://PowerAccessDB.com)
Works great
This is the only script so far that works for me on youtube and pauses all videos from playing on page load, not just up next.