At a bit rate similar to MP3, M4A encoding (based on Advanced Audio Coding, AAC) provides superior sound quality. That's why I decided to use this audio format for the preview and free tracks delivered on this site. The audio quality is the same as what you find on iTunes. M4A format is also natively supported on Apple devices, any modern web browser, and popular video editing software but may require an app to play on specific mobile devices.
You will find more exhaustive information about the m4a format on the Wikipedia page dealing with this subject.
