Scripts for controlling youtube videos. Now maintained at https://github.com/fent/dotfiles/tree/master/scripts

youtube_next.applescript

# If in a playlist, play the next video.
tell application "Google Chrome"
  repeat with t in tabs of windows
    tell t
      if URL starts with "http://www.youtube.com/watch" or URL starts with "https://www.youtube.com/watch" then
        execute javascript "
        var player =
          document.getElementById('movie_player') ||
          document.getElementsByTagName('embed')[0];
        var next = document.getElementsByClassName('yt-uix-button-icon-playlist-bar-next')[0];
        if (player && next) {
          next.click();
        }
        "
        exit repeat
      end if
    end tell
  end repeat
end tell

youtube_pause_all.applescript

# Pause all youtube videos in all youtube tabs.
tell application "Google Chrome"
  repeat with t in tabs of windows
    tell t
      if URL starts with "http://www.youtube.com/watch" or URL starts with "https://www.youtube.com/watch" then
        execute javascript "
        var player =
          document.getElementById('movie_player') ||
          document.getElementsByTagName('embed')[0];
        if (player) {
          player.pauseVideo();
        }
        "
      end if
    end tell
  end repeat
end tell

youtube_play_pause.applescript

# Play or pause a video.
tell application "Google Chrome"
  repeat with t in tabs of windows
    tell t
      if URL starts with "http://www.youtube.com/watch" or URL starts with "https://www.youtube.com/watch" then
        execute javascript "
        var player =
          document.getElementById('movie_player') ||
          document.getElementsByTagName('embed')[0];
        if (player) {
          if (player.getPlayerState() === 1) {
            player.pauseVideo();
          } else {
            player.playVideo();
          }
        }
        "
        exit repeat
      end if
    end tell
  end repeat
end tell

youtube_previous.applescript

# If in a playlist and the current video time is <= 5 seconds,
# play the previous video,
# otherwise, rewind to the beginning of the current video and play.
tell application "Google Chrome"
  repeat with t in tabs of windows
    tell t
      if URL starts with "http://www.youtube.com/watch" or URL starts with "https://www.youtube.com/watch" then
        execute javascript "
        var player =
          document.getElementById('movie_player') ||
          document.getElementsByTagName('embed')[0];
        if (player) {
          var prev = document.getElementsByClassName('yt-uix-button-icon-playlist-bar-prev')[0];
          if (player.getCurrentTime() <= 5 && prev) {
            prev.click();
          } else {
            player.seekTo(0, true);
            if (player.getPlayerState() !== 1) {
              player.playVideo();
            }
          }
        }
        "
        exit repeat
      end if
    end tell
  end repeat
end tell

Does this still work for you with the latest Chrome version? I had a bunch of utility scripts which are all now failing as the js invocation appears to be sandboxed to the vanilla dom api's (no access to page scripts or variables).

These will not work with the latest chrome version anymore. I have created some updated scripts to use with the new chrome version which can be found here https://gist.github.com/zachloubier/9b07fd21292a7dfb92d9.

I used these scripts as inspiration and just replaced the youtube api with vanilla js.

Can you make a script that set a timer to automatically pause on YouTube? On Firefox?