在用解码器解码音频数据得到PCM音频数据块之后，可以在将数据送给声卡播放之前调节其音量大小，具体的实现函数如下：
- void RaiseVolume(char* buf, UINT32 size, UINT32 uRepeat, double vol)//buf为需要调节音量的音频数据块首地址指针，size为长度，uRepeat为重复次数，通常设为1，vol为增益倍数,可以小于1
- {
- if (!size)
- {
- return;
- }
- for (int i = 0; i < size;)
- {
- signed long minData = -0x8000; //如果是8bit编码这里变成-0x80
- signed long maxData = 0x7FFF;//如果是8bit编码这里变成0xFF
- signed short wData = buf[i + 1];
- wData = MAKEWORD(buf[i], buf[i + 1]);
- signed long dwData = wData;
- for (int j = 0; j < uRepeat; j++)
- {
- dwData = dwData * vol;
- if (dwData < -0x8000)
- {
- dwData = -0x8000;
- }
- else if (dwData > 0x7FFF)
- {
- dwData = 0x7FFF;
- }
- }
- wData = LOWORD(dwData);
- buf[i] = LOBYTE(wData);
- buf[i + 1] = HIBYTE(wData);
- i += 2;
- }
- }
