Speedifier is a native Safari 10 extension that lets you control the playback speed of every HTML5 video in Safari. This way, you can watch your favorite videos in double speed or half the speed. If you have an HTML5 video playing on any website, you just need to press right and select the Speedifier option you want to slow down or speed up the playback speed of the video. On some popular pages, Speedifier adds a dedicated button to the video player to control the playback speed.
