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diff --git a/src/audio/README_G711 b/src/audio/README_G711 new file mode 100644 index 0000000..23b0e7d --- /dev/null +++ b/src/audio/README_G711 @@ -0,0 +1,94 @@ +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 + |