How does one play multiple sounds simultaneously on XAudio2? - c++

Question

I am currently trying to make a game app in Windows with XAudio2 and I cannot figure out how to make the application not block when playing a sound. I tried calling a new thread in the samples in this repository.
But it will just cause an error. I tried passing a reference to the mastering voice in the function but then it just raises a "XAudio2: Must create a mastering voice first" error. Am I missing something? I am just trying to make it play two sounds at once and build from there. I went over the documentation but it's very vague.

Answer 1

XAudio2 is a non-blocking API. To play two sounds simultaneously, you need two 'source voices' and one 'mastering voice' at a minimum.
DX::ThrowIfFailed(
CoInitializeEx( nullptr, COINIT_MULTITHREADED )
);
Microsoft::WRL::ComPtr<IXAudio2> pXAudio2;
// Note that only IXAudio2 (and APOs) are COM reference counted
DX::ThrowIfFailed(
XAudio2Create( pXAudio2.GetAddressOf(), 0 )
);
IXAudio2MasteringVoice* pMasteringVoice = nullptr;
DX::ThrowIfFailed(
pXAudio2->CreateMasteringVoice( &pMasteringVoice )
);
IXAudio2SourceVoice* pSourceVoice1 = nullptr;
DX::ThrowIfFailed(
pXaudio2->CreateSourceVoice( &pSourceVoice1, &wfx ) )
// The default 'pSendList' will be just to the pMasteringVoice
);
IXAudio2SourceVoice* pSourceVoice2 = nullptr;
DX::ThrowIfFailed(
pXaudio2->CreateSourceVoice( &pSourceVoice2, &wfx) )
// Doesn't have to be same format as other source voice
// And doesn't have to match the mastering voice either
);
DX::ThrowIfFailed(
pSourceVoice1->SubmitSourceBuffer( &buffer )
);
DX::ThrowIfFailed(
pSourceVoice2->SubmitSourceBuffer( &buffer /* could be different WAV data or not */)
);
DX::ThrowIfFailed(
pSourceVoice1->Start( 0 );
);
DX::ThrowIfFailed(
pSourceVoice2->Start( 0 );
);
You should take a look at the samples on GitHub as well as DirectX Tool Kit for Audio
If you wanted to ensure both source voices started at precisely the same time, you'd use:
DX::ThrowIfFailed(
pSourceVoice1->Start( 0, 1 );
);
DX::ThrowIfFailed(
pSourceVoice2->Start( 0, 1 );
);
DX::ThrowIfFailed(
pSourceVoice2->CommitChanges( 1 );
);

Answer 2

If you want to play multiple sounds simultaneously have a playSound function and launch various threads to play your various sounds each one of a certain source voice.
XAudio2 will take care of mapping each sound to available channels (or if you have a more advanced system you can specify the mapping yourself using IXAudio2Voice::SetOutputMatrix).
void playSound( IXAudio2SourceVoice* sourceVoice )
{
BOOL isPlayingSound = TRUE;
XAUDIO2_VOICE_STATE soundState = {0};
HRESULT hres = sourceVoice->Start( 0u );
while ( SUCCEEDED( hres ) && isPlayingSound )
{// loop till sound completion
sourceVoice->GetState( &soundState );
isPlayingSound = ( soundState.BuffersQueued > 0 ) != 0;
Sleep( 100 );
}
}
For example to play two sounds simultaneously:
IXAudio2SourceVoice* pSourceVoice1 = nullptr;
IXAudio2SourceVoice* pSourceVoice2 = nullptr;
// setup the source voices, load the sounds etc..
std::thread thr1{ playSound, pSourceVoice1 };
std::thread thr2{ playSound, pSourceVoice2 };
thr1.join();
thr2.join();