What is MP3?
MP3 stands for MPEG Audio Layer 3, which revolutionized digital music. Derived from the audio sections of the MPEG-1 and MPEG-2 video specifications, MP3 compresses CD-quality sound by a factor of roughly 10, while retaining most of the original fidelity. MP3 files are played on the computer via media player software, such as Apple's iTunes and Microsoft's Windows Media Player, as well as in countless iPods and other handheld players. While 128 Kbps (kilobits per second) is considered the norm for MP3 files, MP3s can be encoded to bit rates from 8Kbps to 320 Kbps. The higher the bit rate, the better the sound and the larger the file.

What is M4A?
M4A stands for MPEG-4 Audio, and it is a popular audio file format. Most people are familiar with MP3 and how it shrinks down the file size of songs and other audio files. M4A does the same thing as MP3 does, but even better. Quality is better and file sizes are usually smaller than MP3 files.

What is the difference between M4A and MP4 files?
The existance of 2 different file extensions that can be used to represent MPEG 4 Audio files is unfortunate. MP4 files may or may not contain MPEG 4 Audio. If you see a M4A file you always know that it contains only MPEG 4 Audio. MP4 can be used for MPEG 4 video files, combined video and audio files, or just plain MPEG 4 audio. It is recommended that you use the .m4a file extension rather than .mp4 on your audio files.