I run the flash blocker extension in Chrome. So I expect, the next extension I'll be running is a <video> tag blocker with an option to enable on demand. (edit: known as "click to play" mode)
fyi you dont need an extension, Chrome has native click to play support
Or just use an adblocker and you don't have to worry what format the ads are in.
Adblockers don't catch everything, and also on some sites I am happy to support via Ads but I cannot stand being interrupted with auto-play video. I've really enjoyed the complete silence from ads in Flash format and am not looking forward to a repeat of the early 2000s.
+1, I starting using click-to-play _years_ ago as a quick way to make sure that YouTube didn't autoplay when I opened it in a new tab. I don't use ad blockers for ethical reasons, so a pleasant side effect turned out to be neutralizing the most egregious behavior that ads would display (by and large autoplay etc tend to be Flash ads).
Running an adblocker when using Chrome on Android is non-trivial.