Media Players are most often iPod Touches. Break down Mobile Device Type by Mobile Device to see.
For our site we also see traffic from Televisions (Samsung, LG, etc.), Set-top Boxes (Amazon FireTV, Google TV, etc.) and EReaders (Amazon Kindle).
As to why you see hits ... believe it or not, users are coming to your site from these devices (or using some kind of emulator or something that makes them look like those devices). It should be a tiny percentage of traffic though.