Is a media data format created by Apple. Named 'Quicktime' and is opened by a program with the same name. This format contains several tracks, each of which can store audio, video or text. Supported by a large number of encodings and in a single file, each element can use its own codec.
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.