OGG (file format)

Ogg is a patent-free, fully open multimedia bitstream container format designed for efficient streaming and file compression (storage).

The name “Ogg” hence refers to the file format which includes a number of separate independent open source codecs for both audio and video. Files ending in the .ogg extension may be of any Ogg media filetype, and because the format is free, Ogg’s various codecs have been incorporated into a number of different free and commercial media players.

The term “ogg” sometimes refers to the audio file format Ogg Vorbis, that is Vorbis encoded audio in an Ogg container. Other prominent components of Ogg are its video codec Theora, and the human speech audio compression format, Speex.

OGG is very much used by Doom 3, just look in Pak003.pk4 and you see.