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