MediaEngine audio playback on WinRT

问题

I'm trying to add music to my game that runs on WinRT. The music should be in an encoded format (mp3, ogg, etc.) and should be streamable and be decoded by the hardware (for performance reasons).

I've looked through the samples, and found out that MediaEngine can do something like this (I hope).

However, I'm having problems making it work. I keep getting ComExceptions everytime I try to create IMFByteStream from IRandomAccessStream via MFCreateMFByteStreamOnStreamEx().

It might be that I'm not handling tasks correctly, since they are a new paradigm for me.

Here's some code (pretty similar to the sample I mentioned before):

void MyMedia::PlayMusic ()
{
    try
    {
        StorageFolder^ installedLocation = Windows::ApplicationModel::Package::Current->InstalledLocation;

        Concurrency::task<StorageFile^> m_pickFileTask = Concurrency::task<StorageFile^>(installedLocation->GetFileAsync("music.mp3"), m_tcs.get_token());

        SetURL(StringHelper::toString("music.mp3"));

        auto player = this;
        m_pickFileTask.then([&player](StorageFile^ fileHandle)
        {
            Concurrency::task<IRandomAccessStream^> fOpenStreamTask = Concurrency::task<IRandomAccessStream^> (fileHandle->OpenAsync(Windows::Storage::FileAccessMode::Read));
            fOpenStreamTask.then([&player](IRandomAccessStream^ streamHandle)
                {
                    try
                    {
                        player->SetBytestream(streamHandle);

                        if (player->m_spMediaEngine)
                        {
                            MEDIA::ThrowIfFailed(
                                player->m_spMediaEngine->Play()
                                );

                        }
                    } catch(Platform::Exception^)
                    {
                        MEDIA::ThrowIfFailed(E_UNEXPECTED);
                    }

                }
            );  
        }
        );

    } catch(Platform::Exception^ ex)
    {
        Printf("error: %s", ex->Message);
    }


}

void MyMedia::SetBytestream(IRandomAccessStream^ streamHandle)
{
    HRESULT hr = S_OK;
    ComPtr<IMFByteStream> spMFByteStream = nullptr; 

    //The following line always throws a ComException
    MEDIA::ThrowIfFailed(
        MFCreateMFByteStreamOnStreamEx((IUnknown*)streamHandle, &spMFByteStream)
        );

    MEDIA::ThrowIfFailed(
        m_spEngineEx->SetSourceFromByteStream(spMFByteStream.Get(), m_bstrURL)
        );  

    return;
}

Bonus: If you know a better solution to my audio needs, please leave a comment.

回答1:

I managed to fix this. There was two problems I found.

Media Foundation was not initialized

MFStartup(MF_VERSION); needs to be called before Media Foundation can be used. I added this code just before creating the media engine.

Referencing a pointer.

Line m_pickFileTask.then([&player](StorageFile^ fileHandle) should be m_pickFileTask.then([player](StorageFile^ fileHandle). This is already a pointer to the current class, and & provides the address of variable, so I was actually passing the pointer's pointer.

来源：https://stackoverflow.com/questions/11307746/mediaengine-audio-playback-on-winrt

标签

mp3

windows-runtime

ogg