aifccompress(1) aifccompress(1)
NAME
aifccompress - compress the audio data in an AIFF-C file
SYNOPSIS
aifccompress [-v] [-c algorithm] [options] infile.aifc outfile.aifc
DESCRIPTION
aifccompress is a command-line program which reads an AIFF-C digital
audio input file, and copies the header information and sample data to a
compressed AIFF-C digital audio output file.
The output file will contain copies of all the AIFF-C chunks in the
original input file. The chunks may not appear in exactly the same order
as in the original file.
aiffccompress offers compression algorithms which are supported by the
SGI audio file library. They are selected with the -c option. Be sure
to audition to the results before deleting the original sound file. Note
that a signal will degrade with each compression/decompression cycle.
Sound files may have already been subjected to multiple lossy
compressions before they reach your hands. Your next compression may
degrade the signal intolerably. Keep in mind that signal processing
operations such as frequency equalization and reverberation that modify
frequency or phase characteristics may expose the previously masked
(inaudible) heavily quantized portions of the compressed signal when the
significant but mildly quantized portions of the signal are removed or
relatively attenuated.
none No compression. This is the default.
g722 CCITT G.722 ADPCM 4:1 compression recommended for 16-kHz, 16-
bit mono or stereo data. The compression algorithm currently
cannot handle more than two channels. This algorithm is lossy.
ulaw CCITT G.711 mu-law 2:1 compression recommended for 8-kHz, 16-
bit (mono or multichannel) data. This algorithm is lossy.
alaw CCITT G.711 A-law 2:1 compression recommended for 8-kHz, 16-bit
(mono or multichannel) data. This algorithm is lossy.
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awmpeg1 MPEG-1 audio layer 1. Supports single or dual channel 16-bit
input at 32 kHz, 44.1 kHz, or 48 kHz. This algorithm is lossy.
awmpeg2 MPEG-1 audio layer 2. Supports single or dual channel 16-bit
input at 32 kHz, 44.1 kHz, or 48 kHz. This algorithm is lossy.
awmulti Aware MultiRate near-lossless compression typically yielding
compression ratios from 2:1 to 4:1. Supported for single or
dual channel, 16 bit input at 8, 11.025, 16, 22.05, 32, 44.1,
or 48 kHz. This algorithm is lossy.
awlsls Aware MultiRate true lossless compression typically yielding
compression ratios from 1.5:1 to 3:1. Supported for single or
dual channel, 16 bit input at 8, 11.025, 16, 22.05, 32, 44.1,
or 48 kHz. This algorithm is lossless.
The MPEG and Aware MultiRate algorithms take the following additional
options:
-awchanpol
chooses how multiple channels should be treated:
stereo (default for MultiRate)
indicates that the channels are part of a single multi-
channel signal. This includes 4-channel, etc.;
joint (default for MPEG)
indicates that the algorithm may attempt to exploit
redundancy between channels for greater coding gain; Not
valid for MultiRate.
indep
indicates that the separate channels are unrelated and
should be processed separately, such as multilingual sound
tracks.
Note that all of these settings are equivalent for single
channel input.
-awtarg
specifies the desired bitrate for all channels of compressed
data, in bits per second. The following is a list of valid
bitrates for MPEG.
Layer 1:
32000, 64000, 96000, 128000, 160000, 192000, 224000,
256000, 288000, 320000, 352000, 384000, 416000, and
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448000.
Layer 2:
32000, 48000, 56000, 64000, 80000, 96000, 112000, 128000,
160000, 192000, 224000, 256000, 320000, and 384000.
Default value is 192 kbps / channel for layer 1 and 128 kbps /
channel for layer 2. This parameter is not used for Aware's
MultiRate algorithm.
-awbitpol
Provides for different modes of bit assignment: The valid
values depend on the algorithm, as indicated below.
MPEG:
fixed (default)
Fixed bitrate per second.
The Compression ratio is determined by value of
-awtarg.
constqual
Bitrate is driven by the psychoacoustic model.
Enough bits are assigned so that a constant Mask to
Noise ratio is attained. See -awnmr.
Aware MultiRate:
constqual
Enough bits are assigned so that the signal is 90+ dB
above the quantization noise.
Compression ratios are typically between 2.5:1 and
4:1.
lossless
Enough bits are assigned to provide for perfect
reconstruction.
Compression ratios are typically between 2:1 and 3:1.
-awnmr
Not used in the Aware MultiRrate algorithm. For MPEG with -
awbitpol constqual sets the constant quality mode noise-to-
mask ratio in dB. Zero yields a theoretic psychoacoustic
imperceptible compression. Positive values provide more
compression and noise becomes audible. Negative values cause
less compression and less perceptible noise.
with no errors, aifccompress returns 0. If there is an error,
aifccompress returns 1.
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If invoked with no arguments, aifccompress displays help.
If the -v verbose option is specified, aifccompress periodically prints
messages as sample data is copied from the input file to the output file.
The AIFF and AIFF-C file format specifications are published by Apple
Computer Inc.
AUTHOR
Silicon Graphics Inc.
SEE ALSO
playaifc(1), recordaifc(1),
aiff2aifc(1), aifcdecompress(1), aifcresample(1),
dmconvert(1), mediaconvert(1),
MPEG(4), Aware(5)
AIFF-C File Format Specification
AFintro(3A), Introduction to the Audio File Library
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