| Alexandre Lision | 7c6f4a6 | 2013-09-05 13:27:01 -0400 | [diff] [blame] | 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 | |