ac3 Files with the .ac3 filename extension refer to the proprietary audio file format Dolby digital AC-3, developed by Dolby Laboratories. The AC-3 format is from the lossy family of audio compression formats. It supports a variety of audio channel configurations and was the first of its kind to support the full surround sound experience. Because of this, the format has been commonly used in the development of motion picture features designed for theaters and in consumer homes through DVDs and surround sound home theater systems. The AC-3 format is one of the supported audio codecs of the ATSC standard ' a set of standards developed for digital television transmission in several affiliated countries.
ogg The OGG file format and .ogg file extension refer to the open source container format developed and maintained by the Xiph.Org Foundation. The format has been in development since the early 90's and initially was designed as an open format for audio compression. Later iterations has seen the format revised into a full audio and video container format with compression codec support of different standards. OGG can be used both in compressed or uncompressed ways and is compatible with different lossy and lossless codecs both for audio and for video. Text can also be added into OGG files as an overlay, all packaged within a single file.