Video file recorded by Windows Media Center, a program used to play multimedia content and record TV shows; encodes video using MPEG-2 compression and audio using MPEG-1 Layer II or Dolby Digital AC-3 compression; may also include descriptive metadata and digital rights management (DRM) information. The WTV Windows Media Center video format is successor of the DVR-MS Windows Media Center video format and was introduced in Windows 7
this format is free, which apparently is one of the reasons for its popularity. The used codecs supports variable bit rates (as a default), and .ogg files usually play back easily on all platforms. All things being equal, the sound quality exceeds that of mp3 somewhat.