Successor to mp3, m4a (and mp4) made
popular by iTunes and iPods. mp4 is a
container that can store many sub-formats:
Advanced Audio Compression (AAC), of which are different types:
LC (low complexity), HE (high efficiency) to name a few. To
encode your audio to be compatible with most audio players, use
the LC compression type (used as default by this encoder). High
Efficiency (HE AAC) uses SBR technology (not too different as
mp3PRO) if the player knows about HE the extra frequency
information can be decoded, otherwise half the audio quality
will be missing on playback. A newer standard again for ultra
low bitrates is AAC+ or AAC HE v2, this uses parametric stereo
for even lower bitrates, dBpoweramp is able to decode every AAC
type (excluding iTunes m4p protected).
Apples Lossless format (ALAC) this format is
like Zip for audio and looses no audio quality (audio tracks
purchased from Apples iMS store are lossy aac).
these are identical to .m4a except
the iPod knows to use them as audio books and allow book
.m4v are video files.
.m4p protected audio format (tracks purchased from
iTunes Music Store are protected),
whilst dBpoweramp cannot decode these see Forum for
details on fair use.
- .m4a are audio content only,
- .mp4 can contain both audio and video,
Adding ID tags to mp4 has standardized on the Apple iTunes
format, although a competing Nero tagging
format has emerged.
.mp4, .m4p, .aac Encodes
.m4a (Apple Lossless, AAC: LC, HE & HE v2)