音频demo：将PCM数据与alaw、mulaw、g711数据的相互转换

1、README

前言

g711

(截图来源：https://blog.csdn.net/u014470361/article/details/88837776)

我的理解：

首先需要知道的是u-law/a-law是用于脉冲编码的压缩/解压缩算法。而G.711是指在8KHz采样率（单声道）中，使用的u-law或a-law算法对音频进行压缩的一种语音压缩标准。但是，使用这两种压缩算法进行压缩的音频并不一定是G.711，要在8KHz采样率（单声道）的才是，压缩其他采样率和多声道得到的u-law/a-law文件只要设置对应的采样率和声道数照样能解压播放。

a. 编译

demo引用了开源代码g711.c和g711.h，然后在此基础上封装成g711_wraper.c和g711_wraper.h，并编写自己的测试程序main.c进行验证。整个demo程序共5个源文件，可以编译到任意环境下使用（非类Unix系统可能需要简单调整main.c中包含的头文件）：

$ make   # 或者: make CC=your-crosscompile-gcc

b. 使用

examples: ./pcm_alaw_ulaw -h./pcm_alaw_ulaw --help./pcm_alaw_ulaw -m pcm_2_alaw -i ./audio/test_8000_16_1.pcm -o ./test_8000_8_1.g711a./pcm_alaw_ulaw -m pcm_2_ulaw -i ./audio/test_8000_16_1.pcm -o ./test_8000_8_1.g711u./pcm_alaw_ulaw -m alaw_2_pcm -i ./audio/test_8000_8_1.g711a -o ./test_8000_16_1.pcm./pcm_alaw_ulaw -m ulaw_2_pcm -i ./audio/test_8000_8_1.g711u -o ./test_8000_16_1.pcm./pcm_alaw_ulaw -m alaw_2_ulaw -i ./audio/test_8000_8_1.g711a -o ./test_8000_8_1.g711u./pcm_alaw_ulaw -m ulaw_2_alaw -i ./audio/test_8000_8_1.g711u -o ./test_8000_8_1.g711a./pcm_alaw_ulaw --mode pcm_2_ulaw --input_file=./audio/test_8000_16_2.pcm --output_file=./test_8000_8_2.ulaw./pcm_alaw_ulaw --mode pcm_2_ulaw --input_file=./audio/test_22050_16_1.pcm --output_file=./test_22050_8_1.ulaw./pcm_alaw_ulaw --mode pcm_2_alaw --input_file=./audio/test_44100_16_2.pcm --output_file=./test_44100_8_2.alaw...[mode: pcm_2_alaw | pcm_2_ulaw | alaw_2_pcm | ulaw_2_pcm | alaw_2_ulaw | ulaw_2_alaw]

c. demo目录架构

.
├── audio
│   ├── test_22050_16_1.pcm
│   ├── test_22050_8_1.ulaw
│   ├── test_44100_16_2.pcm
│   ├── test_44100_8_2.alaw
│   ├── test_8000_16_1.pcm
│   ├── test_8000_16_2.pcm
│   ├── test_8000_8_1.g711a
│   ├── test_8000_8_1.g711u
│   └── test_8000_8_2.ulaw
├── docs
│   ├── G711编码原理及代码_szfhy的博客-CSDN博客_g711编码.mhtml
│   └── 音频采样及编解码——LPCM 、ADPCM、G711、G726、AAC_夜风的博客-CSDN博客_adpcm.mhtml
├── main.c
├── Makefile
├── pcm_aulaw.c
├── pcm_aulaw.h
├── pcm_aulaw_wraper.c
├── pcm_aulaw_wraper.h
└── README.md

2、主要代码片段

pcm_aulaw.c

/** This source code is a product of Sun Microsystems, Inc. and is provided* for unrestricted use.  Users may copy or modify this source code without* charge.** SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING* THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR* PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.** Sun source code is provided with no support and without any obligation on* the part of Sun Microsystems, Inc. to assist in its use, correction,* modification or enhancement.** SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE* INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE* OR ANY PART THEREOF.** In no event will Sun Microsystems, Inc. be liable for any lost revenue* or profits or other special, indirect and consequential damages, even if* Sun has been advised of the possibility of such damages.** Sun Microsystems, Inc.* 2550 Garcia Avenue* Mountain View, California  94043*/
/** December 30, 1994:* Functions linear2alaw, linear2ulaw have been updated to correctly* convert unquantized 16 bit values.* Tables for direct u- to A-law and A- to u-law conversions have been* corrected.* Borge Lindberg, Center for PersonKommunikation, Aalborg University.* bli@cpk.auc.dk**/
/** Downloaded from comp.speech site in Cambridge.**/#include "pcm_aulaw.h"/** pcm_aulaw.c** u-law, A-law and linear PCM conversions.* Source: http://www.speech.kth.se/cost250/refsys/latest/src/g711.c*/
#define	SIGN_BIT	(0x80)		/* Sign bit for a A-law byte. */
#define	QUANT_MASK	(0xf)		/* Quantization field mask. */
#define	NSEGS		(8)		/* Number of A-law segments. */
#define	SEG_SHIFT	(4)		/* Left shift for segment number. */
#define	SEG_MASK	(0x70)		/* Segment field mask. */static short seg_aend[8] = {0x1F, 0x3F, 0x7F, 0xFF,0x1FF, 0x3FF, 0x7FF, 0xFFF};
static short seg_uend[8] = {0x3F, 0x7F, 0xFF, 0x1FF,0x3FF, 0x7FF, 0xFFF, 0x1FFF};/* copy from CCITT G.711 specifications */
unsigned char _u2a[128] = {			/* u- to A-law conversions */1,	1,	2,	2,	3,	3,	4,	4,5,	5,	6,	6,	7,	7,	8,	8,9,	10,	11,	12,	13,	14,	15,	16,17,	18,	19,	20,	21,	22,	23,	24,25,	27,	29,	31,	33,	34,	35,	36,37,	38,	39,	40,	41,	42,	43,	44,46,	48,	49,	50,	51,	52,	53,	54,55,	56,	57,	58,	59,	60,	61,	62,64,	65,	66,	67,	68,	69,	70,	71,72,	73,	74,	75,	76,	77,	78,	79,
/* corrected:81,	82,	83,	84,	85,	86,	87,	88, should be: */80,	82,	83,	84,	85,	86,	87,	88,89,	90,	91,	92,	93,	94,	95,	96,97,	98,	99,	100,	101,	102,	103,	104,105,	106,	107,	108,	109,	110,	111,	112,113,	114,	115,	116,	117,	118,	119,	120,121,	122,	123,	124,	125,	126,	127,	128};unsigned char _a2u[128] = {			/* A- to u-law conversions */1,	3,	5,	7,	9,	11,	13,	15,16,	17,	18,	19,	20,	21,	22,	23,24,	25,	26,	27,	28,	29,	30,	31,32,	32,	33,	33,	34,	34,	35,	35,36,	37,	38,	39,	40,	41,	42,	43,44,	45,	46,	47,	48,	48,	49,	49,50,	51,	52,	53,	54,	55,	56,	57,58,	59,	60,	61,	62,	63,	64,	64,65,	66,	67,	68,	69,	70,	71,	72,
/* corrected:73,	74,	75,	76,	77,	78,	79,	79,should be: */73,	74,	75,	76,	77,	78,	79,	80,80,	81,	82,	83,	84,	85,	86,	87,88,	89,	90,	91,	92,	93,	94,	95,96,	97,	98,	99,	100,	101,	102,	103,104,	105,	106,	107,	108,	109,	110,	111,112,	113,	114,	115,	116,	117,	118,	119,120,	121,	122,	123,	124,	125,	126,	127};static short search(short val,short *table,short size)
{short i;for (i = 0; i < size; i++) {if (val <= *table++)return (i);}return (size);
}/** linear2alaw() - Convert a 16-bit linear PCM value to 8-bit A-law** linear2alaw() accepts an 16-bit integer and encodes it as A-law data.**		Linear Input Code	Compressed Code*	------------------------	---------------*	0000000wxyza			000wxyz*	0000001wxyza			001wxyz*	000001wxyzab			010wxyz*	00001wxyzabc			011wxyz*	0001wxyzabcd			100wxyz*	001wxyzabcde			101wxyz*	01wxyzabcdef			110wxyz*	1wxyzabcdefg			111wxyz** For further information see John C. Bellamy's Digital Telephony, 1982,* John Wiley & Sons, pps 98-111 and 472-476.*/
unsigned char
linear2alaw(short pcm_val)	/* 2's complement (16-bit range) */
{short	 mask;short	 seg;unsigned char aval;pcm_val = pcm_val >> 3;if (pcm_val >= 0) {mask = 0xD5;		/* sign (7th) bit = 1 */} else {mask = 0x55;		/* sign bit = 0 */pcm_val = -pcm_val - 1;}/* Convert the scaled magnitude to segment number. */seg = search(pcm_val, seg_aend, 8);/* Combine the sign, segment, and quantization bits. */if (seg >= 8)		/* out of range, return maximum value. */return (unsigned char) (0x7F ^ mask);else {aval = (unsigned char) seg << SEG_SHIFT;if (seg < 2)aval |= (pcm_val >> 1) & QUANT_MASK;elseaval |= (pcm_val >> seg) & QUANT_MASK;return (aval ^ mask);}
}/** alaw2linear() - Convert an A-law value to 16-bit linear PCM**/
short
alaw2linear(unsigned char	a_val)
{short t;short seg;a_val ^= 0x55;t = (a_val & QUANT_MASK) << 4;seg = ((unsigned)a_val & SEG_MASK) >> SEG_SHIFT;switch (seg) {case 0:t += 8;break;case 1:t += 0x108;break;default:t += 0x108;t <<= seg - 1;}return ((a_val & SIGN_BIT) ? t : -t);
}#define	BIAS		(0x84)		/* Bias for linear code. */
#define CLIP            8159/*
* linear2ulaw() - Convert a linear PCM value to u-law
*
* In order to simplify the encoding process, the original linear magnitude
* is biased by adding 33 which shifts the encoding range from (0 - 8158) to
* (33 - 8191). The result can be seen in the following encoding table:
*
*	Biased Linear Input Code	Compressed Code
*	------------------------	---------------
*	00000001wxyza			000wxyz
*	0000001wxyzab			001wxyz
*	000001wxyzabc			010wxyz
*	00001wxyzabcd			011wxyz
*	0001wxyzabcde			100wxyz
*	001wxyzabcdef			101wxyz
*	01wxyzabcdefg			110wxyz
*	1wxyzabcdefgh			111wxyz
*
* Each biased linear code has a leading 1 which identifies the segment
* number. The value of the segment number is equal to 7 minus the number
* of leading 0's. The quantization interval is directly available as the
* four bits wxyz.  * The trailing bits (a - h) are ignored.
*
* Ordinarily the complement of the resulting code word is used for
* transmission, and so the code word is complemented before it is returned.
*
* For further information see John C. Bellamy's Digital Telephony, 1982,
* John Wiley & Sons, pps 98-111 and 472-476.
*/
unsigned char
linear2ulaw(short pcm_val)	/* 2's complement (16-bit range) */
{short         mask;short	 seg;unsigned char uval;/* Get the sign and the magnitude of the value. */pcm_val = pcm_val >> 2;if (pcm_val < 0) {pcm_val = -pcm_val;mask = 0x7F;} else {mask = 0xFF;}if ( pcm_val > CLIP ) pcm_val = CLIP;		/* clip the magnitude */pcm_val += (BIAS >> 2);/* Convert the scaled magnitude to segment number. */seg = search(pcm_val, seg_uend, 8);/** Combine the sign, segment, quantization bits;* and complement the code word.*/if (seg >= 8)		/* out of range, return maximum value. */return (unsigned char) (0x7F ^ mask);else {uval = (unsigned char) (seg << 4) | ((pcm_val >> (seg + 1)) & 0xF);return (uval ^ mask);}}/** ulaw2linear() - Convert a u-law value to 16-bit linear PCM** First, a biased linear code is derived from the code word. An unbiased* output can then be obtained by subtracting 33 from the biased code.** Note that this function expects to be passed the complement of the* original code word. This is in keeping with ISDN conventions.*/
short
ulaw2linear(unsigned char	u_val)
{short t;/* Complement to obtain normal u-law value. */u_val = ~u_val;/** Extract and bias the quantization bits. Then* shift up by the segment number and subtract out the bias.*/t = ((u_val & QUANT_MASK) << 3) + BIAS;t <<= ((unsigned)u_val & SEG_MASK) >> SEG_SHIFT;return ((u_val & SIGN_BIT) ? (BIAS - t) : (t - BIAS));
}/* A-law to u-law conversion */
unsigned char
alaw2ulaw(unsigned char	aval)
{aval &= 0xff;return (unsigned char) ((aval & 0x80) ? (0xFF ^ _a2u[aval ^ 0xD5]) :(0x7F ^ _a2u[aval ^ 0x55]));
}/* u-law to A-law conversion */
unsigned char
ulaw2alaw(unsigned char	uval)
{uval &= 0xff;return (unsigned char) ((uval & 0x80) ? (0xD5 ^ (_u2a[0xFF ^ uval] - 1)) :(0x55 ^ (_u2a[0x7F ^ uval] - 1)));
}/* ---------- end of pcm_aulaw.c ----------------------------------------------------- */

pcm_aulaw_wraper.c

#include "pcm_aulaw.h"
#include "pcm_aulaw_wraper.h"void pcm_2_alaw(const short *src_16lepcm, unsigned char *dst_alaw, unsigned int sample_cnt)
{for (int i = 0; i < sample_cnt; i++){dst_alaw[i] = linear2alaw(src_16lepcm[i]);}
}void alaw_2_pcm(const unsigned char *src_alaw, short *dst_16lepcm, unsigned int sample_cnt)
{for (int i = 0; i < sample_cnt; i++){dst_16lepcm[i] = alaw2linear(src_alaw[i]);}
}void pcm_2_ulaw(const short *src_16lepcm, unsigned char *dst_ulaw, unsigned int sample_cnt)
{for (int i = 0; i < sample_cnt; i++){dst_ulaw[i] = linear2ulaw(src_16lepcm[i]);}
}void ulaw_2_pcm(const unsigned char *src_ulaw, short *dst_16lepcm, unsigned int sample_cnt)
{for (int i = 0; i < sample_cnt; i++){dst_16lepcm[i] = ulaw2linear(src_ulaw[i]);}
}void alaw_2_ulaw(const unsigned char *src_alaw, char *dst_ulaw, unsigned int sample_cnt)
{for (int i = 0; i < sample_cnt; i++){dst_ulaw[i] = alaw2ulaw(src_alaw[i]);}
}void ulaw_2_alaw(const unsigned char *src_ulaw, char *dst_alaw, unsigned int sample_cnt)
{for (int i = 0; i < sample_cnt; i++){dst_alaw[i] = ulaw2alaw(src_ulaw[i]);}
}

main.c

#include <stdio.h>
#include <string.h>
#include <getopt.h>
#include <unistd.h>#include "pcm_aulaw_wraper.h"void print_usage(const char *process)
{printf("examples: \n""\t %s -h\n""\t %s --help\n""\t %s -m pcm_2_alaw -i ./audio/test_8000_16_1.pcm -o ./test_8000_8_1.g711a\n""\t %s -m pcm_2_ulaw -i ./audio/test_8000_16_1.pcm -o ./test_8000_8_1.g711u\n""\t %s -m alaw_2_pcm -i ./audio/test_8000_8_1.g711a -o ./test_8000_16_1.pcm\n""\t %s -m ulaw_2_pcm -i ./audio/test_8000_8_1.g711u -o ./test_8000_16_1.pcm\n""\t %s -m alaw_2_ulaw -i ./audio/test_8000_8_1.g711a -o ./test_8000_8_1.g711u\n""\t %s -m ulaw_2_alaw -i ./audio/test_8000_8_1.g711u -o ./test_8000_8_1.g711a\n""\t %s --mode pcm_2_ulaw --input_file=./audio/test_8000_16_2.pcm --output_file=./test_8000_8_2.ulaw\n""\t %s --mode pcm_2_ulaw --input_file=./audio/test_22050_16_1.pcm --output_file=./test_22050_8_1.ulaw\n""\t %s --mode pcm_2_alaw --input_file=./audio/test_44100_16_2.pcm --output_file=./test_44100_8_2.alaw\n""\t ...\n""\t [mode: pcm_2_alaw | pcm_2_ulaw | alaw_2_pcm | ulaw_2_pcm | alaw_2_ulaw | ulaw_2_alaw]\n\n",process, process, process, process, process, process, process, process, process, process, process);
}#define 	BUF_LEN 	(160)int main(int argc, char **argv)
{/* 输入/输出文件 */FILE *fpInput = NULL;FILE *fpOutput = NULL;char inputFileName[128] = {0};char outputFileName[128] = {0};	char inputBuf[BUF_LEN*2] = {0};char outputBuf[BUF_LEN*2] = {0};/* 输入文件与输出文件的转换模式 */	char convert_mode[128] = {0};	if (argc == 1){print_usage(argv[0]);return 0;}/* 解析命令行参数 */char option = 0;int option_index = 0;char *short_options = "hm:i:o:";struct option long_options[] ={{"help",        no_argument,       NULL, 'h'},{"mode",        required_argument, NULL, 'm'},{"input_file",  required_argument, NULL, 'i'},{"output_file", required_argument, NULL, 'o'},{NULL,          0,                 NULL,  0 },};while((option = getopt_long_only(argc, argv, short_options, long_options, &option_index)) != -1){switch(option){case 'h':print_usage(argv[0]);return 0;case 'm':strncpy(convert_mode, optarg, 128);break;case 'i':strncpy(inputFileName, optarg, 128);break;case 'o':strncpy(outputFileName, optarg, 128);break;defalut:printf("Unknown argument!\n");break;}}fpInput = fopen(inputFileName, "rb");if (fpInput == NULL){perror("Open input file error");return -1;}fpOutput = fopen(outputFileName, "wb");if (fpOutput == NULL){perror("Open output file error");return -1;}while(1){/* read data */int readBytes = fread(inputBuf, 1, BUF_LEN, fpInput);if (readBytes <= 0){break;}/* convert and write data */if(0 == strcmp(convert_mode, "pcm_2_alaw")){pcm_2_alaw((const short *)inputBuf, outputBuf, readBytes/2);fwrite(outputBuf, 1, readBytes/2, fpOutput);}else if(0 == strcmp(convert_mode, "pcm_2_ulaw")){pcm_2_ulaw((const short *)inputBuf, outputBuf, readBytes/2);fwrite(outputBuf, 1, readBytes/2, fpOutput);}else if(0 == strcmp(convert_mode, "alaw_2_pcm")){alaw_2_pcm(inputBuf, (short *)outputBuf, readBytes);fwrite(outputBuf, 1, readBytes*2, fpOutput);}else if(0 == strcmp(convert_mode, "ulaw_2_pcm")){ulaw_2_pcm(inputBuf, (short *)outputBuf, readBytes);fwrite(outputBuf, 1, readBytes*2, fpOutput);}else if(0 == strcmp(convert_mode, "alaw_2_ulaw")){alaw_2_ulaw(inputBuf, outputBuf, readBytes);fwrite(outputBuf, 1, readBytes, fpOutput);}else if(0 == strcmp(convert_mode, "ulaw_2_alaw")){ulaw_2_alaw(inputBuf, outputBuf, readBytes);fwrite(outputBuf, 1, readBytes, fpOutput);}else{printf("The convert mode is not supported!\n");goto error_exit;}}printf("\033[32m %s ==> %s Success!\033[0m\n", inputFileName, outputFileName);error_exit:fclose(fpInput);fclose(fpOutput);return 0;
}