AC-3 is the most common version containing up to 6 total channels of sound, with 5 channels of full-bandwidth of 20 Hz - 20 kHz-normal range for speakers (front left and right, center, front, right rear and left rear) and one dedicated output channel for low frequency sounds known as low frequency Effect, or subwoofer. The Dolby Digital format also supports the use of Mono and Stereo. The AC-3 is one of the so-called perceptual compression formats. What it does, basically, is to remove all parts of the original sound, encoded analog, which can not be perceived by the human ear. In this way, it is achieved that the same information is smaller and therefore take up much less physical space. Once achieved compression of the original wave, you can add more information that was not previously possible.
Ogg is a free, open container format, developed and maintained by the Xiph.Org Foundation is unrestricted by software patents and is designed to provide efficient flow diffusion and manipulation of high quality digital multimedia. The Ogg container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata. In the Ogg multimedia framework, Theora provides a layer of lossy video. The audio layer is most commonly provided by the music-oriented Vorbis format but other options include compression codecs Opus, FLAC lossless audio OggPCM.