This tool is used to convert MPEG-4 Audio (m4a) to Ogg Vorbis (ogg).

M4A is a file extension for an audio file encoded with advanced audio coding (AAC) which is a lossy compression. M4A was generally intended as the successor to MP3, which had not been originally designed for audio only but was layer III in an MPEG 1 or 2 video files.

Ogg is a free, open container format maintained by the Xiph.Org Foundation. The creators of the Ogg format claim that it is unrestricted by software patents and is designed to provide for efficient streaming and manipulation of high-quality digital multimedia.