html5media.js enables HTML5 video and audio tags in all major browsers
html5media.info
html5media.info
If so, it leaves your tags alone. If not, it instead uses the Flash-based Flowplayer.
So, you can use the <video> and <audio> tags without worrying about browser support. I've used it several times and it works well.
Does it work with content dynamically inserted into the DOM? A quick glance at the source indicates otherwise.
The Firefox and Safari controls are rather sweet. The Chrome ones are a little basic at the moment.
html5media aims to be the smallest, fastest solution available. It's a little low on features, but it's great for embedding videos with an absolute minimum of fuss and effort.
It's speed should be one of the best out there, as it's a single tiny javascript file that's heavily cached and shared between all websites.