Im building an admin interface for a site, and it would be a great benefit if I could play mkv files in the browser, instead of downloading and then playing them. This doesn't have to be a mainstream technology, since only 3 people will be using the interface.
VLC can also be embedded in a web browser ! For the moment, this function is only available with Mozilla under GNU/Linux. An experimental plugin is also available for Mac OS X and Microsft Windows.