The .M4A file extension identifies as a MPEG-4 Audio Layer file. MPEG-4 encoding is a video streaming file format developed by Apple Corporation and can be played in multimedia players such as Apple's QuickTime. This is a compressed video format which can be used to encode videos without significant quality loss. Since MPEG-4 Part 14 is a container format, MPEG-4 files may contain any number of audio, video, and even subtitle streams, making it impossible to determine the type of streams in an MPEG-4 file based on its filename extension alone. M4A file extension branched out of this concept in order to alleviate the confusion caused by the MP4 file extension, which could be video, or just audio without video, or both.
Many people have questions about M4A, since it is relatively new. M4A stands for MPEG 4 Audio, and it is a popular file extension used to represent audio files. Most people are familiar with MP3 and how it shrinks down the file size of songs and other audio files. M4A and MP4 do the same thing as MP3 does, but even better. Quality is better and file sizes are usually smaller than MP3 files. But unlike MP3, no licenses or payments are required to be able to stream or distribute content in M4A format (unlike MP3 which requires you to pay royalties on content you distribute in MP3 format). This fact alone, is more than enough reason (due to the extreme cost savings) to use M4A files instead of MP3 files. In addition, M4A files tend to sound much better than MP3 files encoded at the same bitrate since it is less "lossy" as an audio compression format.
So what is the difference between M4A and MP4 files? a'ight, no worries! I can hear you !
This is the most popular question we get and seems to cause the most confusion to people who are relatively unaware of the new generation of audio file extensions in use today. I agree with you on this point though that the existence of 2 different file extensions to represent MPEG 4 audio files is rather unfortunate and ultimately unnecessary. Files ending with .MP4 may or may not contain MPEG 4 Audio. On the other hand if you see an M4A file you can deduce that it has to contain MPEG 4 Audio.
MP4 can be used for MPEG 4 video files, combined video and audio files, or just plain MPEG 4 audio. Apple Computer started using and popularizing the M4A file extension denoting that the file has no digital rights management capability. They did this because MP4 was too general (video, video/audio or audio) and could confuse some media players. It is recommended that you use the .m4a file extension rather than .mp4 on your audio files.
Almost all audio players will now play back files using either the .m4a or .mp4 file extension for maximum compatibility. After all, both the .m4a and .mp4 container file formats are the same, they just have different file extensions. If your software program doesn't recognize your file extension, you can rename the file extension to the other one and it should work.
Source by Jon Buchanon