Safari has easy options to set both a default and per-site preferences (https://support.apple.com/guide/safari/stop-autoplay-videos-...), including a "Never Auto-Play" choice. Despite years of user complaints and a fairly clear resolution to them, Chrome either watered-down their fix or solved the wrong problem entirely.
media.autoplay.enabled = false
media.autoplay.enabled.user-gestures-needed = true
This bit is especially infuriating for me, as there seems to be a High Sierra issue with Chrome and videos (for me, at least - it's hard to figure out how widespread it is). They cause massive browser lag when they're on a page for me, to the point of missed characters while typing.
I tried setting the Autoplay policy at the browser level once but found that it was inconsistent and broke certain players. Iridium works perfectly.
However, it does not seem to do much, if anything, for me. I tend to just use Privacy Badger to block any site that looks like a CDN
That won't fix the problem of auto-playing video on CNN or other sites that are not YT. Trying to read news from CNN is still a matter of waiting for the page to load, then wait for the video to load and start playing, then click on the pause button, and voila you can read in peace.
Go to chrome://flags, search for Autoplay policy, and select Document user action is required.
Note that if you use the Imagus extension, this could block some videos/gifs/etc from playing when you hover over a link.
Quoting the blog post, Google’s decision that ”Muted autoplay is always allowed” is the problem. If any other Chrome users wondered why videos now auto-play without sound (even with this option set), at least based on the relatively minimal docs about this flag, this is why.
I can't seem to find the issue, but in the Safari issue tracker, the point was made that given the way HTML5 video and APIs work, it is impossible to reliably prevent autoplay without breaking some sites. It seems that Firefox went for "reliably prevent autoplay" while Chrome went for "without breaking sites".
FWIW, I switched from Chrome to Firefox because of the autoplay issue.