The video player of YouTube supports quite a few keyboard shortcuts to help you quickly skip forward or backward in a video.
For instance, while a video is playing, you can press the ’0′ key to move the play head to the beginning of a video. Press the left or right arrow keys will let you go back or forward in a video by 10%. Alternatively, you may use number keys to jump to specific sections of a video – the key ’1′ will move you to the 10% mark, ’2′ to the 20% mark and so on.
Other than supporting shortcuts, the YouTube player now also lets you alter the playback speed of a video so that you may fast-forward, or slow-down, the video with a click (screenshot).
You may increase the video playback speed by 2x (a 4 minute video will play back in two minutes) or slow it down by a factor of .25 so that the same 4 minute clip takes 16 minutes to play back. Increase the play speed if the video presentation is boring or decrease when you are transcribing what’s being said in the video.
This new option is still being rolled out and may not be available across all YouTube videos.
Also see: Change Playback Speed in QuickTime