AFC (Mass Effect Audio File Container) is an audio container format developed by Canadian video game development company BioWare for their Mass Effect science fiction video game series based on the Unreal 3 Engine.
Being a container format, an AFC file can contain one or multiple audio streams. The audio data stored in AFC files may represent either speech, background music and/or sound effects used in the game.
In its essence, an AFC file is just a regular OGG file with audio data encoded as RIFF WAVE via the WaveWorks Interactive Sound Engine (Wwise). The only thing that makes AFC files different from regular OGG files is the file header, which is slightly different.
AFC files usually have a sampling rate of about 32000Hz at a variable bit rate (VBR) ranging from 75 to about 105kbps. There are currently no desktop media players that provide AFC playback natively. However, there is a good number of independently developed AFC conversion tools such as afc2ogg or the Gibbed Mass Effect 3 Audio Extractor, which allow users to easily convert AFC files to OGG and play them back in any OGG-compatible desktop media player.