Controlling YouTube Replay Speedby Alan Sembera
You can speed up or slow down the playback speed of almost any YouTube video using YouTube's own alternative HTML5 Video Player. The player contains a playback-speed option not found in Adobe Flash player used by YouTube. You can make the HTML5 player your default player from YouTube's website, or you can enable the player only for the videos for which you want to control the playback speed.
Navigate to YouTube's HTML5 Video Player page (link in Resources) and then click "Request the HTML5 Player" to enable the player in your browser.
Navigate to the YouTube page containing the video for which you want to change the playback speed. If you already have the video open, reload the page to load the video using the HTML5 player.
Click the gear icon at the bottom of the video and then change the "Speed" setting to the desired playback speed. You can slow down the video to a quarter of half its original speed, or you can speed it up to twice its normal speed. If you don't see the Speed option, it means YouTube hasn't enabled the video to automatically load in the HTML5 player; however, you can work around this.
Insert the "popup" parameter in the page's URL to load the video in a larger version of the HTML5 Video Player. Replace "watch" in the URL with "watch_popup", so that the final URL looks like "www.youtube.com/watch_popup?v=xXxXXXxXxxX". After you load the video with the new URL, you can access the Speed options from the gear menu in the larger player, just as in the smaller version.