g711 压缩出问题

matthewsq 2008-07-06 12:56:33

传说中g711 压缩是很不错的但是我用他压一个wav文件出现很多杂音（wav格式 8000Hz, 16位 , 立体声）虽然原来的声音还是能听见的。请大家帮我看看问题出在哪里

原代码很简单就是从文件中读取数据 -》压缩-》解压-》播放

			

CG711 g_711[1];

unsigned char g_compressbuff[80000];//从麦克风里获得的然后压缩后的数据

int           g_decompressbuff[80000];//从socket获得然后解压缩后的数据

                  



                  LPVOID lplockbuf;

		DWORD len;

		DWORD dwRead;



		g_pDSBuffer8->Lock(0,0,&lplockbuf,&len,NULL,NULL,DSBLOCK_ENTIREBUFFER);

		g_pWaveFile->Read((BYTE*)lplockbuf,len,&dwRead);



		//压缩 解压

		int *pint=(int *)lplockbuf;

		for(int i=0;i<dwRead/4;i++)//肯定能除以4

		{

			g_compressbuff[i]=g_711[0].linear2alaw(*pint++);//*pint++ 取值然后位置偏移1

		}

		for(int x=0;x<dwRead/4;x++)

		{

			g_decompressbuff[x]=g_711[0].alaw2linear(g_compressbuff[x]);

		}

		memcpy(lplockbuf,(unsigned char*)g_decompressbuff,dwRead);

		g_pDSBuffer8->Unlock(lplockbuf,dwRead,NULL,0);



		//g_pDSBuffer8->Unlock(lplockbuf,len,NULL,0);

		g_pDSBuffer8->SetCurrentPosition(0);

                g_pDSBuffer8->Play(0,0,0/*DSBPLAY_LOOPING*/);

G711类 .cpp
short G_seg_end[8] = {0xFF, 0x1FF, 0x3FF, 0x7FF,0xFFF, 0x1FFF, 0x3FFF, 0x7FFF};
unsigned char G_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,
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, 128};

unsigned char G_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,
73, 74, 75, 76, 77, 78, 79, 79,
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};

.H
#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. */
#define BIAS (0x84) /* Bias for linear code. */

extern short G_seg_end[8];
extern unsigned char G_u2a[128];
extern unsigned char G_a2u[128];

class CG711
{
public :

CG711()
{
memcpy(seg_end,G_seg_end,sizeof(short)*sizeof(seg_end));
memcpy(_u2a ,G_u2a ,sizeof(unsigned char)*sizeof(G_u2a));
memcpy(_a2u ,G_a2u ,sizeof(unsigned char)*sizeof(G_a2u));
}

short seg_end[8];
unsigned char _a2u[128];
unsigned char _u2a[128];
int search(int val,short *table,int size)
{
int i;
for (i = 0; i < size; i++) {
if (val <= *table++)
return (i);
}
return (size);
}

unsigned char linear2alaw(int pcm_val) /* 2's complement (16-bit range) */
{
int mask;
int seg;
unsigned char aval;

if (pcm_val >= 0) {
mask = 0xD5; /* sign (7th) bit = 1 */
} else {
mask = 0x55; /* sign bit = 0 */
pcm_val = -pcm_val - 8;
}

/* Convert the scaled magnitude to segment number. */
seg = search(pcm_val, seg_end, 8);

/* Combine the sign, segment, and quantization bits. */

if (seg >= 8) /* out of range, return maximum value. */
return (0x7F ^ mask);
else {
aval = seg << SEG_SHIFT;
if (seg < 2)
aval |= (pcm_val >> 4) & QUANT_MASK;
else
aval |= (pcm_val >> (seg + 3)) & QUANT_MASK;
return (aval ^ mask);
}
}

int alaw2linear(unsigned char a_val)
{
int t;
int 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);
}
};

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