Is a multimedia container format from Microsoft, which stores video and audio file streams. Distinctive feature is a the lack of information on the coding data. The container defines the structure of the stream so it can, like AVI, contain videos with different codecs, as well as operate during synchronization of streams.
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.