Thanks, SRH! That is really cool! I'll get my son to try it out!Hey, I just found this today: Google provides free a YouTube looper extension for the Chrome browser.
You add the extension here:
Auto replay videos with ONE-CLICK, able to customise features such as AUTO LOOP toggle, setting loop counts and loop portion.chrome.google.com
Then when you're on a YouTube video you get an extra Loop button where you can select the section to loop.
You can use the built-in Playback Speed setting already available in YouTube to set the speed.
It works pretty well, is built-in and free. Not bad.
Here's what it looks like in operation: