The compressionType field of the
common chunk is a case-sensitive
four-character code. There is no public complete register: this list gathers what Apple,
McGill University’s notes, libsndfile and FFmpeg document. Apple defined the first five;
software since has added its own.
Uncompressed PCM
| Type | Name | Audio | Listed by |
|---|---|---|---|
NONE | not compressed | PCM, big-endian | Apple |
twos | PCM, big-endian | libsndfile, FFmpeg | |
sowt | not compressed | PCM, little-endian (the type’s name is “twos” backwards) | Apple |
raw | 8-bit unsigned PCM | libsndfile, FFmpeg | |
in24 | 24-bit PCM, big-endian | libsndfile, FFmpeg | |
in32 | 32-bit PCM, big-endian | libsndfile, FFmpeg | |
ni24 | 24-bit PCM, little-endian | libsndfile | |
ni32 | 32-bit PCM, little-endian | libsndfile |
Floating point
| Type | Name | Audio | Listed by |
|---|---|---|---|
fl32 | 32-bit floating point | IEEE 32-bit float | Apple |
FL32 | Float 32 | IEEE 32-bit float | SoundHack, Csound |
fl64 | 64-bit floating point | IEEE 64-bit float | Apple |
FL64 | IEEE 64-bit float | libsndfile |
Apple’s floats are normalised to a full scale of 1.
Companded
| Type | Name | Audio | Listed by |
|---|---|---|---|
alaw | ALaw 2:1 | 8-bit G.711 A-law | Apple |
ALAW | CCITT G.711 A-law | 8-bit G.711 A-law | SGI |
ulaw | µLaw 2:1 | 8-bit G.711 µ-law | Apple |
ULAW | CCITT G.711 u-law | 8-bit G.711 µ-law | SGI |
QuickTime recognises only the Apple spellings.
Codecs
| Type | Name | Audio | Listed by |
|---|---|---|---|
ACE2 | ACE 2-to-1 | Apple IIGS ACE | Apple |
ACE8 | ACE 8-to-3 | Apple IIGS ACE | Apple |
MAC3 | MACE 3-to-1 | MACE | Apple |
MAC6 | MACE 6-to-1 | MACE | Apple |
ima4 | IMA 4:1 | IMA ADPCM | Apple, libsndfile, FFmpeg |
ADP4 | 4:1 Intel/DVI ADPCM | IMA ADPCM, Audio Convert/Player on AmigaOS | Wikipedia, FFmpeg |
DWVW | Delta with variable word width | TX16W Typhoon | Wikipedia, libsndfile |
GSM | GSM 6.10 | libsndfile, FFmpeg | |
G722 | G.722 ADPCM | FFmpeg | |
G726 | G.726 ADPCM | FFmpeg | |
G728 | G.728 | FFmpeg | |
Qclp | Qualcomm PureVoice | QCELP | Wikipedia, FFmpeg |
QDMC | QDesign Music | QDesign | Wikipedia, FFmpeg |
QDM2 | QDesign Music 2 | FFmpeg | |
rt24 | RT24 50:1 | Voxware | Wikipedia |
rt29 | RT29 50:1 | Voxware | Wikipedia |
SDX2 | Square-Root-Delta | SDX2 DPCM, big-endian | Wikipedia, FFmpeg |
CBD2 | CBD2 DPCM | FFmpeg | |
VAPC | Nintendo 64 VADPCM | FFmpeg |
Apple also maps Microsoft ACM codecs to codes of the form ms??, with the
last two bytes the ACM code, so Microsoft ADPCM (ACM code 1) is the four bytes
ms\0\1.
The details of each codec are outside this format. A reader that does not know a type cannot play the audio, but it can still read the other chunks.