音頻混音算法的實現
1、線性疊加後求平均
優點:不會產生溢出,噪音較小;
缺點:衰減過大,影響通話質量;
short remix(short buffer1,short buffer2)
{
int value = buffer1 + buffer2;
return (short)(value/2);
}
2、歸一化混音(自適應加權混音算法)
思路:使用更多的位數(32 bit)來表示音頻數據的一個樣本,混完音後在想辦法降低其振幅,使其仍舊分佈在16 bit所能表示的範圍之內,這種方法叫做歸一法;
方法:爲避免發生溢出,使用一個可變的衰減因子對語音進行衰減。這個衰減因子也就代表語音的權重,衰減因子隨着音頻數據的變化而變化,所以稱爲自適應加權混音。當溢出時,衰減因子較小,使得溢出的數據在衰減後能夠處於臨界值以內,而在沒有溢出時,又讓衰減因子慢慢增大,使數據較爲平緩的變化。
void Mix(char sourseFile[10][SIZE_AUDIO_FRAME],int number,char *objectFile)
{
//歸一化混音
int const MAX=32767;
int const MIN=-32768;
double f=1;
int output;
int i = 0,j = 0;
for (i=0;i<SIZE_AUDIO_FRAME/2;i++)
{
int temp=0;
for (j=0;j<number;j++)
{
temp+=*(short*)(sourseFile[j]+i*2);
}
output=(int)(temp*f);
if (output>MAX)
{
f=(double)MAX/(double)(output);
output=MAX;
}
if (output<MIN)
{
f=(double)MIN/(double)(output);
output=MIN;
}
if (f<1)
{
f+=((double)1-f)/(double)32;
}
*(short*)(objectFile+i*2)=(short)output;
}
}
if( data1 < 0 && data2 < 0)
date_mix = data1+data2 - (data1 * data2 / -(pow(2,16-1)-1));
else
date_mix = data1+data2 - (data1 * data2 / (pow(2,16-1)-1));
4、切割時間片,重採樣算法
可以把各個通道的聲音疊到一起,讓聲音的採樣率按倍增加,如果提高聲音的播放頻率,聲音可以正常的播放,聲音實現了疊加;如果不想修改聲音的播放輸出頻率,可以通過聲音的重採樣後輸出自己想要的輸出頻率;
5、下面是上面的混音的測試代碼:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define IN_FILE1 "1.wav"
#define IN_FILE2 "2.wav"
#define OUT_FILE "remix.pcm"
#define SIZE_AUDIO_FRAME (2)
void Mix(char sourseFile[10][SIZE_AUDIO_FRAME],int number,char *objectFile)
{
//歸一化混音
int const MAX=32767;
int const MIN=-32768;
double f=1;
int output;
int i = 0,j = 0;
for (i=0;i<SIZE_AUDIO_FRAME/2;i++)
{
int temp=0;
for (j=0;j<number;j++)
{
temp+=*(short*)(sourseFile[j]+i*2);
}
output=(int)(temp*f);
if (output>MAX)
{
f=(double)MAX/(double)(output);
output=MAX;
}
if (output<MIN)
{
f=(double)MIN/(double)(output);
output=MIN;
}
if (f<1)
{
f+=((double)1-f)/(double)32;
}
*(short*)(objectFile+i*2)=(short)output;
}
}
int main()
{
FILE * fp1,*fp2,*fpm;
fp1 = fopen(IN_FILE1,"rb");
fp2 = fopen(IN_FILE2,"rb");
fpm = fopen(OUT_FILE,"wb");
short data1,data2,date_mix;
int ret1,ret2;
char sourseFile[10][2];
while(1)
{
ret1 = fread(&data1,2,1,fp1);
ret2 = fread(&data2,2,1,fp2);
*(short*) sourseFile[0] = data1;
*(short*) sourseFile[1] = data2;
if(ret1>0 && ret2>0)
{
Mix(sourseFile,2,(char *)&date_mix);
/*
if( data1 < 0 && data2 < 0)
date_mix = data1+data2 - (data1 * data2 / -(pow(2,16-1)-1));
else
date_mix = data1+data2 - (data1 * data2 / (pow(2,16-1)-1));*/
if(date_mix > pow(2,16-1) || date_mix < -pow(2,16-1))
printf("mix error\n");
}
else if( (ret1 > 0) && (ret2==0))
{
date_mix = data1;
}
else if( (ret2 > 0) && (ret1==0))
{
date_mix = data2;
}
else if( (ret1 == 0) && (ret2 == 0))
{
break;
}
fwrite(&date_mix,2,1,fpm);
}
fclose(fp1);
fclose(fp2);
fclose(fpm);
printf("Done!\n");
}