What is OGG file?
The Ogg bitstream format, spearheaded by the Xiph.Org Foundation, has been created as the framework of a larger initiative aimed at developing a set of components for the coding and decoding of multimedia content, which are available free of charge and freely re-implementable in software.
The Ogg container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata. The format consists of chunks of data each called an Ogg Page. Each page begins with the "OggS" string to identify the file as Ogg format.
In the Ogg multimedia framework, Theora provides a lossy video layer. The audio layer is most commonly provided by the music-oriented Vorbis format but other options include the human speech compression codec Speex, the lossless audio compression codec FLAC, and OggPCM.