Author: Tomas Rutkauskas

I'm trying to control the left/ right channel volume of a wave. I've checked with 
WaveOutGetDevCaps that volume and left/ right control is supported. When I try to 
read the volume with WaveOutGetVolume (using "word (Wave_Mapper)" as the device), I 
get MMSysErr_NotSupported. I need the original volume setting in order to restore 
it later. WaveOutSetVolume also returns the same error.

Answer:

The code below worked for me. You will see that it is in message handlers for 
WaveOutOpen etc. messages. The key might be that you need the handle to an open 
wave device rather than simply the constant for wave_mapper.


1   procedure TClockForm.mm_wom_open(var Msg: TMessage);
2   {This code handles the WaveOutOpen message by writing two buffers of data
3   to the wave device.  Plus other miscellaneous housekeeping.}
4   begin
5     waveOutGetVolume(hWave_out, @saved_volumes);
6     waveOutSetVolume(hWave_out, volumes);
7     waveOutPrepareHeader(hWave_out, p_wave_hdr, SizeOf(TWaveHdr));
8     waveOutWrite(hWave_out, p_wave_hdr, SizeOf(TWaveHdr));
9   end;
10  
11  procedure TClockForm.mm_wom_done(var Msg: TMessage);
12  {Handle the wave out done message}
13  begin
14    waveOutSetVolume(hWave_out, saved_volumes);
15    waveOutReset(hWave_out);
16    waveOutClose(hWave_out);
17  end;