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实现PCM和ALAW间的转换 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] outfile decode [-3|4|5] [-a|u|l] 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 g721file # Read 40Kbps G.723 and output A-law decode -5 -a alawfile # Compress and then decompress u-law data using 24Kbps G.723 encode -3 ulawout ...展开收缩
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