There is no good on the fly conversion format that a browser can simply play out of the box, like mentioned above, Browsers are actually pretty bad video players. Thats why you need a JavaScript web player around it like we have in Panel that manages the playback, ie. a website that embeds the player.
Thus, there is no URL we can generate that "just plays" right now without several deficits. The streaming conversion is focused on actual players on the users end, like it exists inside JRemote2, or even inside Panel, but its not something a browser can just play without help.
This doesn't mean it can't be done, it just requires a bunch more work. Thats why I suggested involving Brad above, since he made this for Panel and has experience with providing a web site through MC.
If we intend the share feature to primarily be for something you are supposed to play, and not download, then a player page that comes up might make sense for all media types, as it avoids hoping that the browser does the right thing even with eg. audio.