YouTube now defaults to an HTML5 player in modern browsers. While you can choose some varying playback rates from within their interface, this bookmarklet allows you to enter a decimal amount between 0.3
- 3.0
(or slightly wider if you don't mind losing audio).
Add this to the url of your bookmark: javascript: (function(){document.getElementsByTagName('video')[0].playbackRate=prompt('Playback Rate:');})();
Try it with 0.5
on this video for a drunk DHH 🍻
Also works beautifully with @vzaar, and probably many other HTML5 players.