c++ - 媒体基础 : Getting a MediaSink from a SinkWriter

Question

我正在尝试将 MP4 文件接收器添加到拓扑。当我的 MediaSource 已经是 MP4 时，我使用 MFCreateMPEG4MediaSink 和 MF_MPEG4SINK_SPSPPS_PASSTHROUGH。当我的 MediaSource 不是 MP4(来自网络摄像头的原始 YUV)时，我想使用 MFCreateSinkWriterFromURL 这样我就不必弄清楚 MP4 header 和其他复杂的东西。

根据 the MSDN Docs我应该能够使用 GetServiceForStream 获取 MediaSink，因为输入类型与输出类型不同。但是它总是返回 MF_E_UNSUPPORTED_SERVICE。

如何从 MediaSinkWriter 中获取底层的 MediaSink？

或者，我如何轻松地为任意拓扑创建 MP4 媒体接收器？

HRESULT CreateVideoFileSink(
    IMFStreamDescriptor *pSourceSD,     // Pointer to the stream descriptor.
    LPCWSTR pFilename,                  // Name of file to save to.
    IMFStreamSink **ppStream)           // Receives a pointer to the stream sink.
    HRESULT hr = S_OK;
    CComPtr<IMFAttributes> pAttr;
    CComPtr<IMFMediaTypeHandler> pHandler;
    CComPtr<IMFMediaType> pType;
    CComPtr<IMFMediaSink> pSink;
    CComPtr<IMFStreamSink> pStream;
    CComPtr<IMFSinkWriter> pSinkWriter;
    CComPtr<IMFByteStream> pByteStream;

    *ppStream = nullptr;

    // Get the media type handler for the stream.
    IFR(pSourceSD->GetMediaTypeHandler(&pHandler));

    // Get the major media type.
    GUID guidMajorType;
    IFR(pHandler->GetMajorType(&guidMajorType));

    IFR(MFCreateAttributes(&pAttr, 1));
    IFR(pAttr->SetUINT32(MF_READWRITE_ENABLE_HARDWARE_TRANSFORMS, TRUE));

    // Create an output file 
    if (MFMediaType_Video == guidMajorType)
    {
        GUID guidSubType;
        IFR(pHandler->GetCurrentMediaType(&pType));
        IFR(pType->GetGUID(MF_MT_SUBTYPE, &guidSubType));

        if (MFVideoFormat_H264 == guidSubType)
        {
            // ... use MFCreateMPEG4MediaSink
        }
        else
        {
            IFR(MFCreateSinkWriterFromURL(pFilename, nullptr, pAttr, &pSinkWriter));
            DWORD streamIdx;
            IFR(pSinkWriter->AddStream(pType, &streamIdx));
            IFR(pSinkWriter->GetServiceForStream(MF_SINK_WRITER_MEDIASINK, GUID_NULL, IID_PPV_ARGS(&pSink)));
            IFR(pSink->GetStreamSinkByIndex(streamIdx, &pStream));
        }
    }
    else
    {
        // Don't use this stream
        IFR(E_FAIL)
    }

    // Return IMFStreamSink pointer to caller.
    *ppStream = pStream.Detach();

    return S_OK;
}

Answer 1

当然是在写完问题后就想通了。在您调用 BeginWriting 之前，SinkWriter 没有 MediaSink。

IFR(MFCreateSinkWriterFromURL(pFilename, nullptr, pAttr, &pSinkWriter));
DWORD streamIdx;
IFR(pSinkWriter->AddStream(pType, &streamIdx));
IFR(pSinkWriter->BeginWriting()); // <<----
IFR(pSinkWriter->GetServiceForStream(MF_SINK_WRITER_MEDIASINK, GUID_NULL, IID_PPV_ARGS(&pSink)));
IFR(pSink->GetStreamSinkByIndex(streamIdx, &pStream));

(确保在使用 StreamSink 时不要让 SinkWriter 被释放)