Hello! I've been a user of zenphoto for a while now, and I just wrote a quick plugin to support HTML5 video and audio tags. It's quite basic, but it's functional and hopefully will be useful to a number of people.
I'm hosting the project on github, here: https://github.com/rlaskey/zenphoto-html5media so please let me know if you run into any troubles or if there are ways in which you'd like it developed further. In its current version, you just download the .php file and put it in your plugins directory.