interpretor/libsndfile-1.0.25/src/G72x/README.original

   1 The files in this directory comprise ANSI-C language reference implementations
   2 of the CCITT (International Telegraph and Telephone Consultative Committee)
   3 G.711, G.721 and G.723 voice compressions.  They have been tested on Sun
   4 SPARCstations and passed 82 out of 84 test vectors published by CCITT
   5 (Dec. 20, 1988) for G.721 and G.723.  [The two remaining test vectors,
   6 which the G.721 decoder implementation for u-law samples did not pass,
   7 may be in error because they are identical to two other vectors for G.723_40.]
   8
   9 This source code is released by Sun Microsystems, Inc. to the public domain.
  10 Please give your acknowledgement in product literature if this code is used
  11 in your product implementation.
  12
  13 Sun Microsystems supports some CCITT audio formats in Solaris 2.0 system
  14 software.  However, Sun's implementations have been optimized for higher
  15 performance on SPARCstations.
  16
  17
  18 The source files for CCITT conversion routines in this directory are:
  19
  20         g72x.h          header file for g721.c, g723_24.c and g723_40.c
  21         g711.c          CCITT G.711 u-law and A-law compression
  22         g72x.c          common denominator of G.721 and G.723 ADPCM codes
  23         g721.c          CCITT G.721 32Kbps ADPCM coder (with g72x.c)
  24         g723_24.c       CCITT G.723 24Kbps ADPCM coder (with g72x.c)
  25         g723_40.c       CCITT G.723 40Kbps ADPCM coder (with g72x.c)
  26
  27
  28 Simple conversions between u-law, A-law, and 16-bit linear PCM are invoked
  29 as follows:
  30
  31         unsigned char           ucode, acode;
  32         short                   pcm_val;
  33
  34         ucode = linear2ulaw(pcm_val);
  35         ucode = alaw2ulaw(acode);
  36
  37         acode = linear2alaw(pcm_val);
  38         acode = ulaw2alaw(ucode);
  39
  40         pcm_val = ulaw2linear(ucode);
  41         pcm_val = alaw2linear(acode);
  42
  43
  44 The other CCITT compression routines are invoked as follows:
  45
  46         #include "g72x.h"
  47
  48         struct g72x_state       state;
  49         int                     sample, code;
  50
  51         g72x_init_state(&state);
  52         code = {g721,g723_24,g723_40}_encoder(sample, coding, &state);
  53         sample = {g721,g723_24,g723_40}_decoder(code, coding, &state);
  54
  55 where
  56         coding = AUDIO_ENCODING_ULAW    for 8-bit u-law samples
  57                  AUDIO_ENCODING_ALAW    for 8-bit A-law samples
  58                  AUDIO_ENCODING_LINEAR  for 16-bit linear PCM samples
  59
  60
  61
  62 This directory also includes the following sample programs:
  63
  64         encode.c        CCITT ADPCM encoder
  65         decode.c        CCITT ADPCM decoder
  66         Makefile        makefile for the sample programs
  67
  68
  69 The sample programs contain examples of how to call the various compression
  70 routines and pack/unpack the bits.  The sample programs read byte streams from
  71 stdin and write to stdout.  The input/output data is raw data (no file header
  72 or other identifying information is embedded).  The sample programs are
  73 invoked as follows:
  74
  75         encode [-3|4|5] [-a|u|l] <infile >outfile
  76         decode [-3|4|5] [-a|u|l] <infile >outfile
  77 where:
  78         -3      encode to (decode from) G.723 24kbps (3-bit) data
  79         -4      encode to (decode from) G.721 32kbps (4-bit) data [the default]
  80         -5      encode to (decode from) G.723 40kbps (5-bit) data
  81         -a      encode from (decode to) A-law data
  82         -u      encode from (decode to) u-law data [the default]
  83         -l      encode from (decode to) 16-bit linear data
  84
  85 Examples:
  86         # Read 16-bit linear and output G.721
  87         encode -4 -l <pcmfile >g721file
  88
  89         # Read 40Kbps G.723 and output A-law
  90         decode -5 -a <g723file >alawfile
  91
  92         # Compress and then decompress u-law data using 24Kbps G.723
  93         encode -3 <ulawin | deoced -3 >ulawout
  94