M4A: Unprotected audio file
M4A is a file extension for an audio file encoded with advanced audio coding (AAC) which is a loss 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. M4A stands for MPEG 4 Audio. M4A is an unprotected audio file.