Ask HN: How do you deal with encoding HTML5 videos?

I'm working on an iOS app that lets you record video and share it with friends. The videos are currently encoded as MP4 files, which means they play in Chrome and Safari. However, this leaves us with the issue of them not playing in Firefox or other browsers which don't support MP4.

My question is this: How do you deal with this problem? Do you re-encode the videos on the server into a format that works in Firefox/other browsers? Or is there a better way to get more support without having multiple copies of each video?