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
GSM 06.10 Lossy Speech Compression. A lossy format for compressing speech which is used in the Global Standard for Mobile telecommunications (GSM). It’s good for its purpose, shrinking audio data size, but it will introduce lots of noise when a given audio signal is encoded and decoded multiple times. This format is used by some voice mail applications. It is rather CPU intensive.