QuickTime 4 Reference

Constants for Additional Audio Compression Formats

QuickTime 3 defines constants for several additional audio compression formats. These include kFloat32Format and kFloat64Format for single and double precision (i.e., big endian IEEE) floating-point audio. It also defines 'alaw' for aLaw audio. All DV audio from NTSC (format 60) DVC streams is 'dvca', regardless of the format of the data in the frame. In addition, a standard mapping for audio formats present in the Windows Audio Compression Manager is defined.

All ACM audio formats are defined with a 16-bit integer. These are mapped into a QuickTime four-character code by putting 'ms' in the first two characters and the ACM 16-bit value in the second two characters. So the Microsoft ADPCM algorithm (ACM value of 1) has a QuickTime audio compression code of (('MS' << 16) | 1). This enables standard mapping of ACM audio into the QuickTime movie format.

QuickTime has built-in support to decompress the following additional audio formats:

single-precision floating point
double-precision floating point
Microsoft ADPCM (ACM code 1)
Intel/DVI IMA (ACM code 7), DV
aLaw

Both floating-point decompressors support the type siSlopeAndIntercept atom to provide scaling and DC-offset support. QuickTime has the ability to compress the following additional audio formats:

single-precision floating point
double-precision floating point
aLaw

QuickTime 3 and later correctly imports compressed audio from AVI (.avi ) and WAVE (.WAV ) files. The AU file importer has also been enhanced to import aLaw, 8- and 16-bit uncompressed, and single- and double-precision floating point audio in addition to the uLaw that it handled previously. A Sound Designer II file importer has been added. An AU file exporter has been added which can generate aLaw, uLaw, single and double precision floating point, and uncompressed AU files. (Note that most other readers can only handle uLaw, however).

QuickTime 4 is able to import compressed audio in "MP3" format (MPEG 1, layer 3).