95 lines
3.1 KiB
Plaintext
95 lines
3.1 KiB
Plaintext
The files in this directory comprise ANSI-C language reference implementations
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of the CCITT (International Telegraph and Telephone Consultative Committee)
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G.711, G.721 and G.723 voice compressions. They have been tested on Sun
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SPARCstations and passed 82 out of 84 test vectors published by CCITT
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(Dec. 20, 1988) for G.721 and G.723. [The two remaining test vectors,
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which the G.721 decoder implementation for u-law samples did not pass,
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may be in error because they are identical to two other vectors for G.723_40.]
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This source code is released by Sun Microsystems, Inc. to the public domain.
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Please give your acknowledgement in product literature if this code is used
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in your product implementation.
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Sun Microsystems supports some CCITT audio formats in Solaris 2.0 system
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software. However, Sun's implementations have been optimized for higher
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performance on SPARCstations.
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The source files for CCITT conversion routines in this directory are:
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g72x.h header file for g721.c, g723_24.c and g723_40.c
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g711.c CCITT G.711 u-law and A-law compression
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g72x.c common denominator of G.721 and G.723 ADPCM codes
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g721.c CCITT G.721 32Kbps ADPCM coder (with g72x.c)
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g723_24.c CCITT G.723 24Kbps ADPCM coder (with g72x.c)
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g723_40.c CCITT G.723 40Kbps ADPCM coder (with g72x.c)
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Simple conversions between u-law, A-law, and 16-bit linear PCM are invoked
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as follows:
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unsigned char ucode, acode;
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short pcm_val;
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ucode = linear2ulaw(pcm_val);
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ucode = alaw2ulaw(acode);
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acode = linear2alaw(pcm_val);
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acode = ulaw2alaw(ucode);
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pcm_val = ulaw2linear(ucode);
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pcm_val = alaw2linear(acode);
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The other CCITT compression routines are invoked as follows:
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#include "g72x.h"
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struct g72x_state state;
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int sample, code;
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g72x_init_state(&state);
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code = {g721,g723_24,g723_40}_encoder(sample, coding, &state);
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sample = {g721,g723_24,g723_40}_decoder(code, coding, &state);
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where
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coding = AUDIO_ENCODING_ULAW for 8-bit u-law samples
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AUDIO_ENCODING_ALAW for 8-bit A-law samples
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AUDIO_ENCODING_LINEAR for 16-bit linear PCM samples
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This directory also includes the following sample programs:
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encode.c CCITT ADPCM encoder
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decode.c CCITT ADPCM decoder
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Makefile makefile for the sample programs
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The sample programs contain examples of how to call the various compression
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routines and pack/unpack the bits. The sample programs read byte streams from
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stdin and write to stdout. The input/output data is raw data (no file header
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or other identifying information is embedded). The sample programs are
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invoked as follows:
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encode [-3|4|5] [-a|u|l] <infile >outfile
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decode [-3|4|5] [-a|u|l] <infile >outfile
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where:
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-3 encode to (decode from) G.723 24kbps (3-bit) data
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-4 encode to (decode from) G.721 32kbps (4-bit) data [the default]
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-5 encode to (decode from) G.723 40kbps (5-bit) data
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-a encode from (decode to) A-law data
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-u encode from (decode to) u-law data [the default]
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-l encode from (decode to) 16-bit linear data
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Examples:
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# Read 16-bit linear and output G.721
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encode -4 -l <pcmfile >g721file
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# Read 40Kbps G.723 and output A-law
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decode -5 -a <g723file >alawfile
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# Compress and then decompress u-law data using 24Kbps G.723
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encode -3 <ulawin | deoced -3 >ulawout
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