Basically, if you want to stop most all auto playing web videos, you need to not only block Flash and Javascript, but also disable HTML5 auto-play. There are a number of browser plugins for the former, not so much so for the latter.
In Firefox, it's very easy. Just go into
about:config, and type
media.autoplay.enabled in search. Double click to set to
false. Close and re-start Firefox.
Chrome has a free browser extension available
Stop HTML5 Video Autoplay.
I don't know of a direct way of disabling HTML5 auto-play in IE?