waveOutSetVolume

MSDN上说：

MMRESULT waveOutSetVolume(
  HWAVEOUT hwo,  
  DWORD dwVolume 
);

Parameters

hwo

Handle to an open waveform-audio output device. This parameter can also be a device identifier.

dwVolume

New volume setting. The low-order word contains the left-channel volume setting, and the high-order word contains the right-channel setting. A value of 0xFFFF represents full volume, and a value of 0x0000 is silence.

If a device does not support both left and right volume control, the low-order word of dwVolume specifies the volume level, and the high-order word is ignored.

 

{
    waveOutSetVolume(hwo, dwVolume);
    waveOutClose(hwo);
    break;
}

而VLC里面有这么两句：

static int VolumeGet( aout_instance_t * p_aout, audio_volume_t * pi_volume )
{
    DWORD i_waveout_vol;

#ifdef UNDER_CE
    waveOutGetVolume( 0, &i_waveout_vol );
#else
    waveOutGetVolume( p_aout->output.p_sys->h_waveout, &i_waveout_vol );
#endif

    i_waveout_vol &= 0xFFFF;
    *pi_volume = p_aout->output.i_volume =
        (i_waveout_vol * AOUT_VOLUME_MAX + 0xFFFF /*rounding*/) / 2 / 0xFFFF;
    return 0;
}

static int VolumeSet( aout_instance_t * p_aout, audio_volume_t i_volume )
{
    unsigned long i_waveout_vol = i_volume * 0xFFFF * 2 / AOUT_VOLUME_MAX;
    i_waveout_vol |= (i_waveout_vol << 16);

#ifdef UNDER_CE
    waveOutSetVolume( 0, i_waveout_vol );
#else
    waveOutSetVolume( p_aout->output.p_sys->h_waveout, i_waveout_vol );
#endif

    p_aout->output.i_volume = i_volume;
    return 0;
}