Video support for studies

[Siderite]

So the Chessmood site (and probably many others) have a video, followed by some puzzles based on that video. Since Lichess does allow YouTube videos (hopefully in study pages as well) then it would be great if we could encode "video chapters"

[Siderite]

Suggestion:

• replace URLs in the embed format (https://www.youtube.com/embed/AaV3Oun5PDE?autoplay=1&autohide=0&showinfo=0&rel=0&disablekb=1) which allows creators to specify parameters
• the fullscreen option will be disabled if possible, since lichess doesn't allow it
• the origin and widget_referrer will be set automatically by the code
• what about autoplay?
• where to replace the URL (not everywhere in Lichess, right?)
• take into account a study you contribute to, Preview mode and study you don't contribute to and non interactive chapter
• take into account desktop and mobile
• what's the actual flow: show board and video? video replaces board? Can you start a video and then continue to other moves with it picture-in-picture? do you show the image in the interactive bubble? Maybe a video per chapter or too restrictive?

More about parameters: https://developers.google.com/youtube/player_parameters

[Siderite]

Example of a working iframe:

<iframe 
  title="Bobby Fischer's 21-move brilliancy" 
  width="100%"
  height="100%" 
  frameborder="0" 
  allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" 
  allowfullscreen=""
  src="https://www.youtube.com/embed/AaV3Oun5PDE?autoplay=1&amp;state=1&amp;start=2&amp;autoplay=1&amp;autohide=0&amp;showinfo=0&amp;rel=0"
  credentialless=""
/>

[Siderite]

What about enablejsapi? Could a video be connected to specific moves at different times or something?