I have tried these kinds of extensions before, and it always seems easier to just press "<" on my keyboard to slow down the video and ">" to speed it up, which is supported by default on YouTube.
People need to use tamper monkey. Not that you can just find tons of scripts that just do the trick, sometimes it's rather easy to get things done:<p>Just create a new script on Youtube and add:<p><pre><code> document.getElementsByTagName('video')[0].playbackRate=1.5
</code></pre>
Set the start to "document-end" et voila.
I'm a heavy user of Video Speed Controller [1] but it requires you alter the speed from 1x for every video. When exercising, doing housework, or anything away from the computer, I usually want informational content to continue humming along at ~1.5x speed. This tiny extension adjusts the speed to 1.5x speed without you needing to do anything.<p><a href="https://chromewebstore.google.com/detail/video-speed-controller/nffaoalbilbmmfgbnbgppjihopabppdk?hl=en" rel="nofollow">https://chromewebstore.google.com/detail/video-speed-control...</a>