I've been working all day on firefox bug 517363. This bug is to fix video poster frame scaling. For example, if you have a video with a 4:3 aspect ratio, but you set the video element to be 500px high and wide, the poster image will be stretched to fit the entire video element, while the video is scaled to maintain its aspect ratio. Clearly, the poster frame should also be scaled.
At this point, I'm no closer to understanding what to do than when I started. I've identified places where poster image things are happening in the code. I'm not entirely sure how the poster frame gets displayed though. I need a deeper understanding of how a video element goes through the steps leading up to when the poster is displayed. Probably a task for tomorrow.
I've managed to get the image to appear with the correct aspect ratio by deleting code :P
Unfortunately its being not being drawn in the center... that I'll need to work on some more..