[jholman]

I wrote a bookmarklet. Works on all non-iframe audio and video.

javascript:void%20function(){document.querySelector(%22video,audio%22).playbackRate=parseFloat(prompt(%22Set%20the%20playback rate%22))}();

Here's a non-interactive version

javascript:void%20function(){document.querySelector(%22audio,video%22).playbackRate=2.7}();