Commons uses the freely-licensed Ogg and WebM formats http://commons.wikimedia.org/wiki/Commons:File_types#Sound for media files; unfortunately these are not supported by default in Safari and Internet Explorer, as Apple and Microsoft favor a competing format. Manual codec installation goes against modern user expectations, and isn't possible in some environments.

I've spent some research time working on ogv.js https://github.com/brion/ogv.js, which uses Mozilla's emscripten http://emscripten.org/ and Adobe's CrossBridge http://adobe-flash.github.io/crossbridge/ to cross-compile the Ogg Vorbis and Theora codecs to JavaScript and Flash. This allows decoding and playing Ogg media in the browser without additional software installation.

Here's a live demo wiki with ogv.js embedded into the player widget: http://ogvjs-testing.wmflabs.org/wiki/Demo

On Firefox, Chrome, or Opera you'll continue to get native Ogg or WebM playback; on Safari 6.1/7 and iOS 7 Mobile Safari you get the JavaScript Ogg player, and on IE 9/10/11 you get the Flash Ogg player. (Microsoft lists Web Audio as "in development http://status.modern.ie/webaudioapi" for future IE versions, which will enable use of the pure JS version there as well.)

This is very much a work in progress, but I'm pretty confident this is something we can deploy later this year to get basic A/V playback to "just work" for another chunk of our users.

I'll be presenting some further status updates & related topics at my Wikimania talk.

Note that the Flash code used for IE is entirely open-source and uses none of the proprietary multimedia codecs built into Flash. I consider this a delightfully subversive use of Flash, and it would please me no end to get it deployed on Wikimedia. :)

-- brion