VLC Media Player (v1.1 on-wards) can play YouTube videos without affecting the sound pitch and without having to download the video separately.
Here are the steps:
- Go to
File
->Open Network Stream
menu option. - Paste in the main YouTube video URL (Example URL: http://www.youtube.com/watch?v=Ew_tdY0V4Zo).
- Hit the
Play
button. Change the video playback speed of the video using keyboard shortcuts[
to decrease or]
to increase speed.
UPDATE: You can have more control over YouTube's default HTML5 speed settings (without the audio pitch issue). Speed up YouTube Playback?Speed up YouTube Playback?