How to stop auto start of videos

The above trick from Macintouch worked for me, stopping annoying autoplay of video on news websites:

open Terminal app, paste and enter these two lines of code...

defaults write com.apple.Safari "com.apple.Safari.ContentPageGroupIdentifier.WebKit2RequiresUserGestureForMedia Playback" -bool true

defaults write com.apple.Safari WebKitVideoPlaybackRequiresUserGesture -bool true

That is a function of the website, so there isn't much you can do.

The easiest way I have found is the use Chrome or Firefox, both have extensions that will stop autoplay. I use Disable HTML5 Autoplay in Chrome and used to have a similar one for Flash but have all Flash plugins turned off or deleted. I tried Safari 10 after updating to Sierra and found the autoplay intolerable and searched the web unsuccessfully for solutions. Unfortunately Safari always seems to lag years behind the other main browsers in the kind of extension functionality I need to control the internet annoyances.

At least for some sites (CNN, MacWorld) this solution worked for me:

https://www.macintouch.com/forums/showthread.php?pid=6359#pid6359

Restart Safari after running these particular Terminal commands.