音频demo：将PCM数据与g726数据的相互转换

R-QWERT2024-07-09 13:56

1、README

前言

本demo是将使用了开源项目EasyAACEncoder里的src/g726.cpp(demo中的已重命名为g726.c)和src/g726.h将16位小字节序的pcm数据和g726进行相互转换。

注：相关测试文件已存放在demo的audio目录下，目前发现pcm转换得到的g726文件用软件Audacity播放不正常（没找到g726，所以选的VOX ADPCM），而将所得到的g726再转换回pcm却播放正常，网上说需要支持g726解码的播放器才能播放，用ffmpeg播放也出错，所以看到本注释时的g726都是播放不了的。

a. 编译
bash 复制代码 
$ make clean && make # 或者`make DEBUG=1`打开调试打印信息，又或者指定`CC=your-crosscompile-gcc`进行编译交叉编译
b. 使用
bash 复制代码 
$ ./pcm_g726_convert
Usage:
   ./pcm_g726_convert -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 16000 -o out_8khz_16kbps.g726
   ./pcm_g726_convert -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 24000 -o out_8khz_24kbps.g726
   ./pcm_g726_convert -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 32000 -o out_8khz_32kbps.g726
   ./pcm_g726_convert -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 40000 -o out_8khz_40kbps.g726
   ./pcm_g726_convert -t g726_2_pcm -i ./audio/test_8khz_16kbps.g726 -r 16000 -o out_8khz_16bit_mono_128kbps-1.pcm
   ./pcm_g726_convert -t g726_2_pcm -i ./audio/test_8khz_24kbps.g726 -r 24000 -o out_8khz_16bit_mono_128kbps-2.pcm
   ./pcm_g726_convert -t g726_2_pcm -i ./audio/test_8khz_32kbps.g726 -r 32000 -o out_8khz_16bit_mono_128kbps-3.pcm
   ./pcm_g726_convert -t g726_2_pcm -i ./audio/test_8khz_40kbps.g726 -r 40000 -o out_8khz_16bit_mono_128kbps-4.pcm
c. 参考文章
d. demo目录架构
bash 复制代码 
$ tree
.
├── audio
│   ├── test_8khz_16bit_mono_128kbps.pcm
│   ├── test_8khz_16kbps.g726
│   ├── test_8khz_24kbps.g726
│   ├── test_8khz_32kbps.g726
│   └── test_8khz_40kbps.g726
├── docs
│   ├── g726算法的一些总结_那年晴天的博客-CSDN博客.mhtml
│   ├── g726转pcm_ybn187的专栏-CSDN博客_g726转pcm.mhtml
│   └── 音频采样及编解码------LPCM 、ADPCM、G711、G726、AAC_夜风的博客-CSDN博客_adpcm.mhtml
├── g726.c
├── g726.h
├── main.c
├── Makefile
└── README.md

2、主要代码片段

g726.c
c 复制代码 
/*
	Copyright (c) 2013-2016 EasyDarwin.ORG.  All rights reserved.
	Github: https://github.com/EasyDarwin
	WEChat: EasyDarwin
	Website: http://www.easydarwin.org
*/

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include "g726.h"

static const int qtab_726_16[1] =
{
    261
};

static const int qtab_726_24[3] =
{
    8, 218, 331
};

static const int qtab_726_32[7] =
{
    -124, 80, 178, 246, 300, 349, 400
};

static const int qtab_726_40[15] =
{
    -122, -16,  68, 139, 198, 250, 298, 339,
     378, 413, 445, 475, 502, 528, 553
};


static __inline int top_bit(unsigned int bits)
{
#if defined(__i386__)  ||  defined(__x86_64__)
	int res;

	__asm__ (" xorl %[res],%[res];\n"
		" decl %[res];\n"
		" bsrl %[bits],%[res]\n"
		: [res] "=&r" (res)
		: [bits] "rm" (bits));
	return res;
#elif defined(__ppc__)  ||   defined(__powerpc__)
	int res;

	__asm__ ("cntlzw %[res],%[bits];\n"
		: [res] "=&r" (res)
		: [bits] "r" (bits));
	return 31 - res;
#elif defined(_M_IX86) // Visual Studio x86
	__asm
	{
		xor eax, eax
			dec eax
			bsr eax, bits
	}
#else
	int res;

	if (bits == 0)
		return -1;
	res = 0;
	if (bits & 0xFFFF0000)
	{
		bits &= 0xFFFF0000;
		res += 16;
	}
	if (bits & 0xFF00FF00)
	{
		bits &= 0xFF00FF00;
		res += 8;
	}
	if (bits & 0xF0F0F0F0)
	{
		bits &= 0xF0F0F0F0;
		res += 4;
	}
	if (bits & 0xCCCCCCCC)
	{
		bits &= 0xCCCCCCCC;
		res += 2;
	}
	if (bits & 0xAAAAAAAA)
	{
		bits &= 0xAAAAAAAA;
		res += 1;
	}
	return res;
#endif
}


static bitstream_state_t *bitstream_init(bitstream_state_t *s)
{
	if (s == NULL)
		return NULL;
	s->bitstream = 0;
	s->residue = 0;
	return s;
}

/*
 * Given a raw sample, 'd', of the difference signal and a
 * quantization step size scale factor, 'y', this routine returns the
 * ADPCM codeword to which that sample gets quantized.  The step
 * size scale factor division operation is done in the log base 2 domain
 * as a subtraction.
 */
static short quantize(int d,                  /* Raw difference signal sample */
                        int y,                  /* Step size multiplier */
                        const int table[],     /* quantization table */
                        int quantizer_states)   /* table size of short integers */
{
    short dqm;    /* Magnitude of 'd' */
    short exp;    /* Integer part of base 2 log of 'd' */
    short mant;   /* Fractional part of base 2 log */
    short dl;     /* Log of magnitude of 'd' */
    short dln;    /* Step size scale factor normalized log */
    int i;
    int size;

    /*
     * LOG
     *
     * Compute base 2 log of 'd', and store in 'dl'.
     */
    dqm = (short) abs(d);
    exp = (short) (top_bit(dqm >> 1) + 1);
    /* Fractional portion. */
    mant = ((dqm << 7) >> exp) & 0x7F;
    dl = (exp << 7) + mant;

    /*
     * SUBTB
     *
     * "Divide" by step size multiplier.
     */
    dln = dl - (short) (y >> 2);

    /*
     * QUAN
     *
     * Search for codword i for 'dln'.
     */
    size = (quantizer_states - 1) >> 1;
    for (i = 0;  i < size;  i++)
    {
        if (dln < table[i])
            break;
    }
    if (d < 0)
    {
        /* Take 1's complement of i */
        return (short) ((size << 1) + 1 - i);
    }
    if (i == 0  &&  (quantizer_states & 1))
    {
        /* Zero is only valid if there are an even number of states, so
           take the 1's complement if the code is zero. */
        return (short) quantizer_states;
    }
    return (short) i;
}
/*- End of function --------------------------------------------------------*/


/*
* returns the integer product of the 14-bit integer "an" and
* "floating point" representation (4-bit exponent, 6-bit mantessa) "srn".
*/
static short fmult(short an, short srn)
{
	short anmag;
	short anexp;
	short anmant;
	short wanexp;
	short wanmant;
	short retval;

	anmag = (an > 0)  ?  an  :  ((-an) & 0x1FFF);
	anexp = (short) (top_bit(anmag) - 5);
	anmant = (anmag == 0)  ?  32  :  (anexp >= 0)  ?  (anmag >> anexp)  :  (anmag << -anexp);
	wanexp = anexp + ((srn >> 6) & 0xF) - 13;

	wanmant = (anmant*(srn & 0x3F) + 0x30) >> 4;
	retval = (wanexp >= 0)  ?  ((wanmant << wanexp) & 0x7FFF)  :  (wanmant >> -wanexp);

	return (((an ^ srn) < 0)  ?  -retval  :  retval);
}

/*
* Compute the estimated signal from the 6-zero predictor.
*/
static __inline short predictor_zero(g726_state_t *s)
{
	int i;
	int sezi;

	sezi = fmult(s->b[0] >> 2, s->dq[0]);
	/* ACCUM */
	for (i = 1;  i < 6;  i++)
		sezi += fmult(s->b[i] >> 2, s->dq[i]);
	return (short) sezi;
}
/*- End of function --------------------------------------------------------*/

/*
* Computes the estimated signal from the 2-pole predictor.
*/
static __inline short predictor_pole(g726_state_t *s)
{
	return (fmult(s->a[1] >> 2, s->sr[1]) + fmult(s->a[0] >> 2, s->sr[0]));
}

/*
* Computes the quantization step size of the adaptive quantizer.
*/
static int step_size(g726_state_t *s)
{
	int y;
	int dif;
	int al;

	if (s->ap >= 256)
		return s->yu;
	y = s->yl >> 6;
	dif = s->yu - y;
	al = s->ap >> 2;
	if (dif > 0)
		y += (dif*al) >> 6;
	else if (dif < 0)
		y += (dif*al + 0x3F) >> 6;
	return y;
}
/*- End of function --------------------------------------------------------*/

/*
* Returns reconstructed difference signal 'dq' obtained from
* codeword 'i' and quantization step size scale factor 'y'.
* Multiplication is performed in log base 2 domain as addition.
*/
static short reconstruct(int sign,    /* 0 for non-negative value */
						 int dqln,    /* G.72x codeword */
						 int y)       /* Step size multiplier */
{
	short dql;    /* Log of 'dq' magnitude */
	short dex;    /* Integer part of log */
	short dqt;
	short dq;     /* Reconstructed difference signal sample */

	dql = (short) (dqln + (y >> 2));  /* ADDA */

	if (dql < 0)
		return ((sign)  ?  -0x8000  :  0);
	/* ANTILOG */
	dex = (dql >> 7) & 15;
	dqt = 128 + (dql & 127);
	dq = (dqt << 7) >> (14 - dex);
	return ((sign)  ?  (dq - 0x8000)  :  dq);
}
/*- End of function --------------------------------------------------------*/

/*
* updates the state variables for each output code
*/
static void update(g726_state_t *s,
				   int y,       /* quantizer step size */
				   int wi,      /* scale factor multiplier */
				   int fi,      /* for long/short term energies */
				   int dq,      /* quantized prediction difference */
				   int sr,      /* reconstructed signal */
				   int dqsez)   /* difference from 2-pole predictor */
{
	short mag;
	short exp;
	short a2p;        /* LIMC */
	short a1ul;       /* UPA1 */
	short pks1;       /* UPA2 */
	short fa1;
	short ylint;
	short dqthr;
	short ylfrac;
	short thr;
	short pk0;
	int i;
	int tr;

	a2p = 0;
	/* Needed in updating predictor poles */
	pk0 = (dqsez < 0)  ?  1  :  0;

	/* prediction difference magnitude */
	mag = (short) (dq & 0x7FFF);
	/* TRANS */
	ylint = (short) (s->yl >> 15);            /* exponent part of yl */
	ylfrac = (short) ((s->yl >> 10) & 0x1F);  /* fractional part of yl */
	/* Limit threshold to 31 << 10 */
	thr = (ylint > 9)  ?  (31 << 10)  :  ((32 + ylfrac) << ylint);
	dqthr = (thr + (thr >> 1)) >> 1;            /* dqthr = 0.75 * thr */
	if (!s->td)                                 /* signal supposed voice */
		tr = 0;
	else if (mag <= dqthr)                      /* supposed data, but small mag */
		tr = 0;                             /* treated as voice */
	else                                        /* signal is data (modem) */
		tr = 1;

	/*
	* Quantizer scale factor adaptation.
	*/

	/* FUNCTW & FILTD & DELAY */
	/* update non-steady state step size multiplier */
	s->yu = (short) (y + ((wi - y) >> 5));

	/* LIMB */
	if (s->yu < 544)
		s->yu = 544;
	else if (s->yu > 5120)
		s->yu = 5120;

	/* FILTE & DELAY */
	/* update steady state step size multiplier */
	s->yl += s->yu + ((-s->yl) >> 6);

	/*
	* Adaptive predictor coefficients.
	*/
	if (tr)
	{
		/* Reset the a's and b's for a modem signal */
		s->a[0] = 0;
		s->a[1] = 0;
		s->b[0] = 0;
		s->b[1] = 0;
		s->b[2] = 0;
		s->b[3] = 0;
		s->b[4] = 0;
		s->b[5] = 0;
	}
	else
	{
		/* Update the a's and b's */
		/* UPA2 */
		pks1 = pk0 ^ s->pk[0];

		/* Update predictor pole a[1] */
		a2p = s->a[1] - (s->a[1] >> 7);
		if (dqsez != 0)
		{
			fa1 = (pks1)  ?  s->a[0]  :  -s->a[0];
			/* a2p = function of fa1 */
			if (fa1 < -8191)
				a2p -= 0x100;
			else if (fa1 > 8191)
				a2p += 0xFF;
			else
				a2p += fa1 >> 5;

			if (pk0 ^ s->pk[1])
			{
				/* LIMC */
				if (a2p <= -12160)
					a2p = -12288;
				else if (a2p >= 12416)
					a2p = 12288;
				else
					a2p -= 0x80;
			}
			else if (a2p <= -12416)
				a2p = -12288;
			else if (a2p >= 12160)
				a2p = 12288;
			else
				a2p += 0x80;
		}

		/* TRIGB & DELAY */
		s->a[1] = a2p;

		/* UPA1 */
		/* Update predictor pole a[0] */
		s->a[0] -= s->a[0] >> 8;
		if (dqsez != 0)
		{
			if (pks1 == 0)
				s->a[0] += 192;
			else
				s->a[0] -= 192;
		}
		/* LIMD */
		a1ul = 15360 - a2p;
		if (s->a[0] < -a1ul)
			s->a[0] = -a1ul;
		else if (s->a[0] > a1ul)
			s->a[0] = a1ul;

		/* UPB : update predictor zeros b[6] */
		for (i = 0;  i < 6;  i++)
		{
			/* Distinguish 40Kbps mode from the others */
			s->b[i] -= s->b[i] >> ((s->bits_per_sample == 5)  ?  9  :  8);
			if (dq & 0x7FFF)
			{
				/* XOR */
				if ((dq ^ s->dq[i]) >= 0)
					s->b[i] += 128;
				else
					s->b[i] -= 128;
			}
		}
	}

	for (i = 5;  i > 0;  i--)
		s->dq[i] = s->dq[i - 1];
	/* FLOAT A : convert dq[0] to 4-bit exp, 6-bit mantissa f.p. */
	if (mag == 0)
	{
		s->dq[0] = (dq >= 0)  ?  0x20  :  0xFC20;
	}
	else
	{
		exp = (short) (top_bit(mag) + 1);
		s->dq[0] = (dq >= 0)
			?  ((exp << 6) + ((mag << 6) >> exp))
			:  ((exp << 6) + ((mag << 6) >> exp) - 0x400);
	}

	s->sr[1] = s->sr[0];
	/* FLOAT B : convert sr to 4-bit exp., 6-bit mantissa f.p. */
	if (sr == 0)
	{
		s->sr[0] = 0x20;
	}
	else if (sr > 0)
	{
		exp = (short) (top_bit(sr) + 1);
		s->sr[0] = (short) ((exp << 6) + ((sr << 6) >> exp));
	}
	else if (sr > -32768)
	{
		mag = (short) -sr;
		exp = (short) (top_bit(mag) + 1);
		s->sr[0] =  (exp << 6) + ((mag << 6) >> exp) - 0x400;
	}
	else
	{
		s->sr[0] = (short) 0xFC20;
	}

	/* DELAY A */
	s->pk[1] = s->pk[0];
	s->pk[0] = pk0;

	/* TONE */
	if (tr)                 /* this sample has been treated as data */
		s->td = 0;      /* next one will be treated as voice */
	else if (a2p < -11776)  /* small sample-to-sample correlation */
		s->td = 1;       /* signal may be data */
	else                    /* signal is voice */
		s->td = 0;

	/* Adaptation speed control. */
	/* FILTA */
	s->dms += ((short) fi - s->dms) >> 5;
	/* FILTB */
	s->dml += (((short) (fi << 2) - s->dml) >> 7);

	if (tr)
		s->ap = 256;
	else if (y < 1536)                      /* SUBTC */
		s->ap += (0x200 - s->ap) >> 4;
	else if (s->td)
		s->ap += (0x200 - s->ap) >> 4;
	else if (abs((s->dms << 2) - s->dml) >= (s->dml >> 3))
		s->ap += (0x200 - s->ap) >> 4;
	else
		s->ap += (-s->ap) >> 4;
}

/*
* Decodes a 2-bit CCITT G.726_16 ADPCM code and returns
* the resulting 16-bit linear PCM, A-law or u-law sample value.
*/
static short g726_16_decoder(g726_state_t *s, unsigned char code)
{
	short sezi;
	short sei;
	short se;
	short sr;
	short dq;
	short dqsez;
	int y;

	/* Mask to get proper bits */
	code &= 0x03;
	sezi = predictor_zero(s);
	sei = sezi + predictor_pole(s);

	y = step_size(s);
	dq = reconstruct(code & 2, g726_16_dqlntab[code], y);

	/* Reconstruct the signal */
	se = sei >> 1;
	sr = (dq < 0)  ?  (se - (dq & 0x3FFF))  :  (se + dq);

	/* Pole prediction difference */
	dqsez = sr + (sezi >> 1) - se;

	update(s, y, g726_16_witab[code], g726_16_fitab[code], dq, sr, dqsez);

	return (sr << 2);
}
/*- End of function --------------------------------------------------------*/


/*
 * Encodes a linear PCM, A-law or u-law input sample and returns its 3-bit code.
 */
static unsigned char g726_16_encoder(g726_state_t *s, short amp)
{
    int y;
    short sei;
    short sezi;
    short se;
    short d;
    short sr;
    short dqsez;
    short dq;
    short i;
    
    sezi = predictor_zero(s);
    sei = sezi + predictor_pole(s);
    se = sei >> 1;
    d = amp - se;

    /* Quantize prediction difference */
    y = step_size(s);
    i = quantize(d, y, qtab_726_16, 4);
    dq = reconstruct(i & 2, g726_16_dqlntab[i], y);

    /* Reconstruct the signal */
    sr = (dq < 0)  ?  (se - (dq & 0x3FFF))  :  (se + dq);

    /* Pole prediction difference */
    dqsez = sr + (sezi >> 1) - se;
    
    update(s, y, g726_16_witab[i], g726_16_fitab[i], dq, sr, dqsez);
    return (unsigned char) i;
}

/*
* Decodes a 3-bit CCITT G.726_24 ADPCM code and returns
* the resulting 16-bit linear PCM, A-law or u-law sample value.
*/
static short g726_24_decoder(g726_state_t *s, unsigned char code)
{
	short sezi;
	short sei;
	short se;
	short sr;
	short dq;
	short dqsez;
	int y;

	/* Mask to get proper bits */
	code &= 0x07;
	sezi = predictor_zero(s);
	sei = sezi + predictor_pole(s);

	y = step_size(s);
	dq = reconstruct(code & 4, g726_24_dqlntab[code], y);

	/* Reconstruct the signal */
	se = sei >> 1;
	sr = (dq < 0)  ?  (se - (dq & 0x3FFF))  :  (se + dq);

	/* Pole prediction difference */
	dqsez = sr + (sezi >> 1) - se;

	update(s, y, g726_24_witab[code], g726_24_fitab[code], dq, sr, dqsez);

	return (sr << 2);
}
/*- End of function --------------------------------------------------------*/


/*
 * Encodes a linear PCM, A-law or u-law input sample and returns its 3-bit code.
 */
static unsigned char g726_24_encoder(g726_state_t *s, short amp)
{
    short sei;
    short sezi;
    short se;
    short d;
    short sr;
    short dqsez;
    short dq;
    short i;
    int y;
    
    sezi = predictor_zero(s);
    sei = sezi + predictor_pole(s);
    se = sei >> 1;
    d = amp - se;

    /* Quantize prediction difference */
    y = step_size(s);
    i = quantize(d, y, qtab_726_24, 7);
    dq = reconstruct(i & 4, g726_24_dqlntab[i], y);

    /* Reconstruct the signal */
    sr = (dq < 0)  ?  (se - (dq & 0x3FFF))  :  (se + dq);

    /* Pole prediction difference */
    dqsez = sr + (sezi >> 1) - se;
    
    update(s, y, g726_24_witab[i], g726_24_fitab[i], dq, sr, dqsez);
    return (unsigned char) i;
}


/*
* Decodes a 4-bit CCITT G.726_32 ADPCM code and returns
* the resulting 16-bit linear PCM, A-law or u-law sample value.
*/
static short g726_32_decoder(g726_state_t *s, unsigned char code)
{
	short sezi;
	short sei;
	short se;
	short sr;
	short dq;
	short dqsez;
	int y;

	/* Mask to get proper bits */
	code &= 0x0F;
	sezi = predictor_zero(s);
	sei = sezi + predictor_pole(s);

	y = step_size(s);
	dq = reconstruct(code & 8, g726_32_dqlntab[code], y);

	/* Reconstruct the signal */
	se = sei >> 1;
	sr = (dq < 0)  ?  (se - (dq & 0x3FFF))  :  (se + dq);

	/* Pole prediction difference */
	dqsez = sr + (sezi >> 1) - se;

	update(s, y, g726_32_witab[code], g726_32_fitab[code], dq, sr, dqsez);

	return (sr << 2);
}
/*- End of function --------------------------------------------------------*/

/*
 * Encodes a linear input sample and returns its 4-bit code.
 */
static unsigned char g726_32_encoder(g726_state_t *s, short amp)
{
    short sei;
    short sezi;
    short se;
    short d;
    short sr;
    short dqsez;
    short dq;
    short i;
    int y;
    
    sezi = predictor_zero(s);
    sei = sezi + predictor_pole(s);
    se = sei >> 1;
    d = amp - se;

    /* Quantize the prediction difference */
    y = step_size(s);
    i = quantize(d, y, qtab_726_32, 15);
    dq = reconstruct(i & 8, g726_32_dqlntab[i], y);

    /* Reconstruct the signal */
    sr = (dq < 0)  ?  (se - (dq & 0x3FFF))  :  (se + dq);

    /* Pole prediction difference */
    dqsez = sr + (sezi >> 1) - se;

    update(s, y, g726_32_witab[i], g726_32_fitab[i], dq, sr, dqsez);
    return (unsigned char) i;
}

/*
* Decodes a 5-bit CCITT G.726 40Kbps code and returns
* the resulting 16-bit linear PCM, A-law or u-law sample value.
*/
static short g726_40_decoder(g726_state_t *s, unsigned char code)
{
	short sezi;
	short sei;
	short se;
	short sr;
	short dq;
	short dqsez;
	int y;

	/* Mask to get proper bits */
	code &= 0x1F;
	sezi = predictor_zero(s);
	sei = sezi + predictor_pole(s);

	y = step_size(s);
	dq = reconstruct(code & 0x10, g726_40_dqlntab[code], y);

	/* Reconstruct the signal */
	se = sei >> 1;
	sr = (dq < 0)  ?  (se - (dq & 0x7FFF))  :  (se + dq);

	/* Pole prediction difference */
	dqsez = sr + (sezi >> 1) - se;

	update(s, y, g726_40_witab[code], g726_40_fitab[code], dq, sr, dqsez);

	return (sr << 2);
}
/*- End of function --------------------------------------------------------*/


/*
 * Encodes a 16-bit linear PCM, A-law or u-law input sample and retuens
 * the resulting 5-bit CCITT G.726 40Kbps code.
 */
static unsigned char g726_40_encoder(g726_state_t *s, short amp)
{
    short sei;
    short sezi;
    short se;
    short d;
    short sr;
    short dqsez;
    short dq;
    short i;
    int y;
    
    sezi = predictor_zero(s);
    sei = sezi + predictor_pole(s);
    se = sei >> 1;
    d = amp - se;

    /* Quantize prediction difference */
    y = step_size(s);
    i = quantize(d, y, qtab_726_40, 31);
    dq = reconstruct(i & 0x10, g726_40_dqlntab[i], y);

    /* Reconstruct the signal */
    sr = (dq < 0)  ?  (se - (dq & 0x7FFF))  :  (se + dq);

    /* Pole prediction difference */
    dqsez = sr + (sezi >> 1) - se;

    update(s, y, g726_40_witab[i], g726_40_fitab[i], dq, sr, dqsez);
    return (unsigned char) i;
}

g726_state_t *g726_init(g726_state_t *s, int bit_rate)
{
	int i;

	if (bit_rate != 16000  &&  bit_rate != 24000  &&  bit_rate != 32000  &&  bit_rate != 40000)
		return NULL;

	s->yl = 34816;
	s->yu = 544;
	s->dms = 0;
	s->dml = 0;
	s->ap = 0;
	s->rate = bit_rate;

	for (i = 0; i < 2; i++)
	{
		s->a[i] = 0;
		s->pk[i] = 0;
		s->sr[i] = 32;
	}
	for (i = 0; i < 6; i++)
	{
		s->b[i] = 0;
		s->dq[i] = 32;
	}
	s->td = 0;
	switch (bit_rate)
	{
	case 16000:
		s->enc_func = g726_16_encoder;
		s->dec_func = g726_16_decoder;
		s->bits_per_sample = 2;
		break;
	case 24000:
		s->enc_func = g726_24_encoder;
		s->dec_func = g726_24_decoder;
		s->bits_per_sample = 3;
		break;
	case 32000:
	default:
		s->enc_func = g726_32_encoder;
		s->dec_func = g726_32_decoder;
		s->bits_per_sample = 4;
		break;
	case 40000:
		s->enc_func = g726_40_encoder;
		s->dec_func = g726_40_decoder;
		s->bits_per_sample = 5;
		break;
	}
	bitstream_init(&s->bs);
	return s;
}

int g726_decode(g726_state_t *s,
				short amp[],
				const unsigned char g726_data[],
				int g726_bytes)
{
	int i;
	int samples;
	unsigned char code;
	int sl;

	for (samples = i = 0;  ;  )
	{
		if (s->bs.residue < s->bits_per_sample)
		{
			if (i >= g726_bytes)
				break;
			s->bs.bitstream = (s->bs.bitstream << 8) | g726_data[i++];
			s->bs.residue += 8;
		}
		code = (unsigned char) ((s->bs.bitstream >> (s->bs.residue - s->bits_per_sample)) & ((1 << s->bits_per_sample) - 1));

		s->bs.residue -= s->bits_per_sample;

		sl = s->dec_func(s, code);

		amp[samples++] = (short) sl;
	}
	return samples;
}


int g726_encode(g726_state_t *s,
                unsigned char g726_data[],
                const short amp[],
                int len)
{
    int i;
    int g726_bytes;
    short sl;
    unsigned char code;

    for (g726_bytes = i = 0;  i < len;  i++)
    {
		sl = amp[i] >> 2;

        code = s->enc_func(s, sl);

		s->bs.bitstream = (s->bs.bitstream << s->bits_per_sample) | code;
		s->bs.residue += s->bits_per_sample;
		if (s->bs.residue >= 8)
		{
			g726_data[g726_bytes++] = (unsigned char) ((s->bs.bitstream >> (s->bs.residue - 8)) & 0xFF);
			s->bs.residue -= 8;
		}
		
    }
	
    return g726_bytes;
}
main.c
c 复制代码 
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>

#include "g726.h"

// 编译时Makefile里控制
#ifdef ENABLE_DEBUG
	#define DEBUG(fmt, args...)     printf(fmt, ##args)
#else
	#define DEBUG(fmt, args...)
#endif

#define BUF_SIZE 	2048	


void print_Usage(char *processName)
{
	printf("Usage: \n"
		   "   %s -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 16000 -o out_8khz_16kbps.g726\n"
		   "   %s -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 24000 -o out_8khz_24kbps.g726\n"
		   "   %s -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 32000 -o out_8khz_32kbps.g726\n"
		   "   %s -t pcm_2_g726 -i ./audio/test_8khz_16bit_mono_128kbps.pcm -r 40000 -o out_8khz_40kbps.g726\n"
		   "   %s -t g726_2_pcm -i ./audio/test_8khz_16kbps.g726 -r 16000 -o out_8khz_16bit_mono_128kbps-1.pcm\n"
		   "   %s -t g726_2_pcm -i ./audio/test_8khz_24kbps.g726 -r 24000 -o out_8khz_16bit_mono_128kbps-2.pcm\n"
		   "   %s -t g726_2_pcm -i ./audio/test_8khz_32kbps.g726 -r 32000 -o out_8khz_16bit_mono_128kbps-3.pcm\n"
		   "   %s -t g726_2_pcm -i ./audio/test_8khz_40kbps.g726 -r 40000 -o out_8khz_16bit_mono_128kbps-4.pcm\n",
		   processName, processName, processName, processName, processName, processName, processName, processName);
}


int main(int argc, char *argv[])
{
	unsigned int bitRates = 0;
	unsigned char *inBuf = (unsigned char *)malloc(BUF_SIZE);
	unsigned char *outBuf = (unsigned char *)malloc(BUF_SIZE);
	char convertType[128];
	char inputFileName[128];
	char outputFileName[128];
	FILE *fpInput = NULL;
	FILE *fpOutput = NULL;
	g726_state_t *g726Handler = NULL; // g726操作句柄

	if(argc == 1)
	{
		print_Usage(argv[0]);
		return -1;
	}

	// 解析命令行参数 -- start --
	char option = 0;
	int option_index = 0;
	const char *short_options = "ht:i:o:r:";
	struct option long_options[] =
	{
		{"help",         no_argument,       NULL, 'h'},
		{"convert_type", required_argument, NULL, 't'},
		{"input_file", 	 required_argument, NULL, 'i'},
		{"output_file",  required_argument, NULL, 'o'},
		{"bit_rates",    required_argument, NULL, 'r'},
		{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 't':
				strncpy(convertType, optarg, 128);
				break;
			case 'i':
				strncpy(inputFileName, optarg, 128);
				break;
			case 'o':
				strncpy(outputFileName, optarg, 128);
				break;
			case 'r':
				bitRates = atoi(optarg);
				break;
			defalut:
				printf("Unknown argument!\n");
				break;
		}
	}
	// 解析命令行参数 -- end --
	printf("\n**************************************\n"
		   "convert type: %s\n"
		   "input file name: %s\n"
		   "output file name: %s\n"
		   "g726 bit rates: %d bps\n"
		   "**************************************\n\n",
		   !strcmp(convertType, "pcm_2_g726") ? "pcm -> g726" : "g726 -> pcm",
		   inputFileName, outputFileName, bitRates);


	fpInput  = fopen(inputFileName, "rb");
	fpOutput = fopen(outputFileName, "wb");
	if(!fpInput || !fpOutput)
	{
		printf("Open Input/Output file failed!\n");
		return -1;
	}

	// step 1: 先分配内存空间给操作句柄
	g726Handler = (g726_state_t *)malloc(sizeof(g726_state_t));
	if(g726Handler == NULL)
	{
		printf("Alloc memory for g726 handler failed!\n");
		return -1;
	}

	// step 2: 根据比特率（码率）进行初始化得到句柄
	g726Handler = g726_init(g726Handler, bitRates);

	// 按一"帧"160个采样点进行操作
	#define SAMPLES_PER_FRAME 	(160)

	if(strcmp(convertType, "pcm_2_g726") == 0) // encode
	{
		int readBytes = -1;
		int ret = -1;

		while(1)
		{
			readBytes = fread(inBuf, 1, SAMPLES_PER_FRAME*(16/8), fpInput);
			if(readBytes <= 0)
				break;

			/* 参数：句柄、g726缓存（传出）、pcm缓存（传入）、pcm的采样点个数；
			 * 返回值：编码得到的g726数据长度
			 */
			ret = g726_encode(g726Handler, (unsigned char*)outBuf, (const short*)inBuf, readBytes/2); // 记得读到的字节数要除以2
			DEBUG("[g726_encode]  read pcm bytes: %d  ->  encode g726 bytes: %d\n", readBytes, ret);
			if(ret != readBytes * bitRates / 128000)
			{
				printf("PCM encode to G726 failed!\n");
				printf("\033[31mFailed!\033[0m\n");
				break;
			}

			fwrite(outBuf, 1, ret, fpOutput);
		}
	}
	else if(strcmp(convertType, "g726_2_pcm") == 0) // decode
	{
		int readBytes = -1;
		int ret = -1;

		while(1)
		{
			readBytes = fread(inBuf, 1, SAMPLES_PER_FRAME * (16/8) * bitRates / 128000, fpInput);
			if(readBytes <= 0)
				break;

			/* 参数：句柄、pcm缓存（传出）、g726缓存（传入）、g726数据长度；
			 * 返回值：pcm的采样点个数，注意不是字节数！！！所以字节数是要x2
			 */
			ret = g726_decode(g726Handler, (short*)outBuf, inBuf, readBytes);
			DEBUG("[g726_decode] read g726 bytes: %d  ->  decode pcm bytes: %d\n", readBytes, ret*2);
			if(ret*2 * bitRates / 128000 != readBytes)
			{
				printf("G726 decode to PCM failed!\n");
				printf("\033[31mFailed!\033[0m\n");
				break;
			}

			fwrite(outBuf, 2, ret, fpOutput);
		}
	}
	else
	{
		printf("Unknown convert type!\n");
		printf("\033[31mFailed!\033[0m\n");
		return -1;
	}

	printf("\033[32msuccess!\033[0m\n");

	// step : 释放句柄的内存
	free(g726Handler);

	free(inBuf);
	free(outBuf);
	fclose(fpInput);
	fclose(fpOutput);

	return 0;
}

3、demo下载地址（任选一个）

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