This m4a codec handles:
- Apple Lossless:
audio compression, encoding and decoding supported (16 & 24 bit)
- Advanced Audio Compression
also known as AAC: a lossy compression like mp3,
decoding supported (installed on demand). To encode AAC install the
m4a Nero AAC Encoder.
m4a is a container, it can contain
either Apple Lossless or AAC.
Portions of the ALAC codec are (c) Apple and are
licensed under the Apache License.
Supported by this Codec
- Encoding: Yes
[.m4a (Apple Lossless, for AAC see m4a Nero AAC Encoder) ]
- Multi-processor Encoding: Yes
(with dBpoweramp reference)
- Decoding: Yes
[.m4a, .mp4, .m4b]
- ID Tag Reading: Yes
- ID Tag Writing: Yes
- Unicode Tagging:
- Supports Album Art: Yes
- Gapless Encoding & Decoding: Yes
- Explorer Audio Popup Information:
- Explorer Columns: Yes
- Unicode Filenames: Yes
Windows 98 or newer, dBpoweramp
R12 or newer required.
Lossless Compression Options
Apple Lossless does not have many options, it does not
need any (being lossless).
After Encoding Verify.... will read
back the compressed file and compare it with source audio ensuring error
free compression (both hardware & codec are verified).
mp3, m4a (and mp4) is a container that can store many sub-formats:
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).
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 HEv2, this uses parametric stereo for even lower bitrates,
dBpoweramp is able to decode every AAC type (excluding iTunes m4p
- .m4a are audio content only,
- .mp4 can contain both audio and video,
identical to .m4a except the iPod knows to use them as audio books
and allow book marking,
- .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
Adding ID tags to mp4 has standardized on the Apple iTunes format,
although a competing (read, non-compatible) Nero tagging format has
dBpoweramp Configuration offers advanced options for
this codec (dBpoweramp Configuration >> Codecs >> Advanced Options):
m4a / mp4 Tagging
can be 'Optimized for
Streaming' (where the audio details and tags are placed before audio
data), or 'Streaming Incompatible' where audio data appears first.
by using a
padding, minor tag changes save the whole file being shuffled (as
tags are generally before the audio)
Compatibility Sony and Nokia
players require an id3v1 tag, whilst strictly breaking the m4a
standard, this option will write those for compatibility.
m4a / mp4 Decoder
Output (AAC) 16 bit, 24 or 32 bit gives the
option to select the output from the decoder, 32 bit is
automatically selected when an encoder can use the higher
resolution. AAC stores internally encodings as floating point, but
generally speaking encoding a 16 bit audio CD to Ogg Vorbis then
back to 32 bit point wave will not yield extra bit depth. This
option requires dBpoweramp Reference.
Corrupt AAC File gives the option to continue
decoding an aac file after a stream error has been detected (ie
corrupt audio file), or stop on such an error.
Complete Version Changes
Huge thanks go to David Hammerton, for his work on reverse
engineering the Apple Lossless format.