From the specification information:
Media RSS extends enclosures to handle other media types, such as short films or TV, as well as provide additional metadata with the media. Media RSS enables content publishers and bloggers to syndicate multimedia content such as TV and video clips, movies, images, and audio.
Yahoo is continuing to pump out great user enhancing tools – even more facsinating, Yahoo worked with organizations like Creative Commons and Ourmedia on the specification. Users were able to get involved with the development of the specification through the rss-media group.
Yahoo has gone through alot of effort to produce tools that we can extend for our own needs. By placing the control and initiative into our hands – Yahoo is allowing us to catalog and extend metadata for our media.