It's never going to happen on XP.

Depends on whether XP outlasts the H.264 patents (currently 2028 but they like to keep adding new patents to these pools to extend the time they have lock in for).

So I'd say it's 50/50.

2028? Its incredible how we're using 18th century understanding of intellectual property in the modern age. The monied interests have really figured out how to game this broken system.