I remember 12 years ago, while the Flash vs Html war was still raging on (pre-html5), I created a framework to create web video playback using CSS and JPEGs. It would expect a set of big JPEGs, each containing the frames of the video in a grid (a "reel"), and play it by changing the css background position (and swap out the background with the next jpeg once a "reel" was complete).

It worked really well, and I also cloned the (at the time) Youtube player UI. Seeking, keyframes, flexible framerate, etc were all supported out of the box thanks to the simple underlying architecture.

https://github.com/VAS/animite