I was watching some of the videos the other day and trying to take notes and trying to rewind 10 to 20 seconds (especially on mobile) can be tough and having a jump back button would be pretty helpful.
I dunno about you but my iPhone has a built in skip back 15 seconds button. And I use it a lot.
My phone doesn’t have it, though I wish it did.
Mirai is limited to the functionality in the player they use, but for the Chrome browser, there’s an extension called Video Speed Controller that allows you to control the speed the video plays (say if you want to cruise through an old Q&A at 1.2 speed), but it has a handy skip back and skip forward button. This one is only for Chrome on a desktop/laptop, but there may be other versions for the browser of your choice. Video Speed Controller - Chrome Web Store
On mobile, iPhone is the only one with the skip back/forward option. I’ve looked for things on Android but haven’t found any options.