My wife and I were watching Mr. Palfrey of Westminster on Acorn, and the aspect ratio on s2e1 was 11% off. It was really annoying me (especially before I realized it was just that one episode that was bad). So I wrote a little bookmarklet to adjust the aspect ratio of all html5 videos in a web page.
Here it is: Stretch Video.
To use it, drag it from the above link to your browser’s bookmark bar (which you can show and hide in Chrome with shift-ctrl-b). Then when you have the video on your screen, click on the bookmark and enter the horizontal and vertical stretch ratios, or the correct aspect ratio.
For full-screen video, try first resizing and then switching to full-screen (on some websites, like YouTube, there will be a one second delay before the video stretches on full-screen toggle). (On Firefox, you can also pull up bookmarks in full-screen mode with shift-ctrl-b, which helps.)
To cancel the effect, just reload your video page.
And for fun, here is a Video Rate bookmarklet (we wouldn't want to treat space very differently from time, would we?).
Public domain source code is here.
