视频特效滤镜 via Media Foundation Transform (MFT)

视频特效定义

视频特效（Video effects 或 Visual effects）是对每帧图像进行各种数字化处理达到的效果。如对画面的尺寸、位置、亮度及色度等参数进行处理，就可获得缩放、旋转、黑白、油画等各种效果。

常见的特效技术有：缩放、旋转、裁剪、叠加、老电影、黑白、淡入淡出、水印、去噪、慢动作、2D 转 3D 等等。

Media Foundation Transform

MF 中插件是以 MFT 的形式创建的，需要继承 IMFTransform 接口，接口函数如下：

// Methods That Handle Format Negotiation
STDMETHODIMP GetStreamLimits(DWORD *pInputMinimum, DWORD *pInputMaximum, DWORD *pOutputMinimum, DWORD *pOutputMaximum);
STDMETHODIMP GetStreamCount(DWORD *pcInputStreams, DWORD *pcOutputStreams);
STDMETHODIMP GetStreamIDs(DWORD dwInputIDArraySize, DWORD *pdwInputIDs, DWORD dwOutputIDArraySize, DWORD *pdwOutputIDs);
STDMETHODIMP GetInputStreamInfo(DWORD dwInputStreamID, MFT_INPUT_STREAM_INFO *pStreamInfo);
STDMETHODIMP GetOutputStreamInfo(DWORD dwOutputStreamID, MFT_OUTPUT_STREAM_INFO *pStreamInfo);
STDMETHODIMP GetAttributes(IMFAttributes **ppAttributes);
STDMETHODIMP GetInputStreamAttributes(DWORD dwInputStreamID, IMFAttributes **ppAttributes);
STDMETHODIMP GetOutputStreamAttributes(DWORD dwOutputStreamID, IMFAttributes **ppAttributes);
STDMETHODIMP GetInputAvailableType(DWORD dwInputStreamID, DWORD dwTypeIndex, IMFMediaType **ppType);
STDMETHODIMP GetOutputAvailableType(DWORD dwOutputStreamID, DWORD dwTypeIndex, IMFMediaType **ppType);
STDMETHODIMP SetInputType(DWORD dwInputStreamID, IMFMediaType *pType, DWORD dwFlags);
STDMETHODIMP SetOutputType(DWORD dwOutputStreamID, IMFMediaType *pType, DWORD dwFlags);

// Methods That Specify or Retrieve State Information
STDMETHODIMP GetInputCurrentType(DWORD dwInputStreamID, IMFMediaType **ppType);
STDMETHODIMP GetOutputCurrentType(DWORD dwOutputStreamID, IMFMediaType **ppType);
STDMETHODIMP DeleteInputStream(DWORD dwStreamID);
STDMETHODIMP AddInputStreams(DWORD cStreams, DWORD *adwStreamIDs);
STDMETHODIMP GetInputStatus(DWORD dwInputStreamID, DWORD *pdwFlags);
STDMETHODIMP GetOutputStatus(DWORD *pdwFlags);
STDMETHODIMP SetOutputBounds(LONGLONG hnsLowerBound, LONGLONG hnsUpperBound);

// Methods That Handle Buffering and Processing Data
STDMETHODIMP ProcessEvent(DWORD dwInputStreamID, IMFMediaEvent *pEvent);
STDMETHODIMP ProcessMessage(MFT_MESSAGE_TYPE eMessage, ULONG_PTR ulParam);
STDMETHODIMP ProcessInput(DWORD dwInputStreamID, IMFSample *pSample, DWORD dwFlags);
STDMETHODIMP ProcessOutput(DWORD dwFlags, DWORD cOutputBufferCount, MFT_OUTPUT_DATA_BUFFER *pOutputSamples, DWORD *pStatus);

如果要实现一个 异步的 MFT，则还需要继承 IMFMediaEventGenerator 和 IMFShutdown 接口。

// IMFMediaEventGenerator
HRESULT BeginGetEvent(IMFAsyncCallback *pCallback, IUnknown *punkState);
HRESULT EndGetEvent(IMFAsyncResult *pResult, IMFMediaEvent **ppEvent);
HRESULT GetEvent(DWORD dwFlags, IMFMediaEvent **ppEvent);
HRESULT QueueEvent(MediaEventType met, REFGUID guidExtendedType, HRESULT hrStatus, const PROPVARIANT *pvValue);

// IMFShutdown
HRESULT GetShutdownStatus(MFSHUTDOWN_STATUS *pStatus);
HRESULT Shutdown();

下面介绍一下 IMFTransform 的几个比较重要的接口，以一个灰度化视频的插件为例。
代码包含在 Windows SDK 7.x 的 samples\multimedia\mediafoundation\mft_grayscale\ 目录下。

IMFTransform::GetInputStreamInfo 函数

对输入流的要求，比如视频 sample 必须完整且只有一个 buffer，流的大小等等。

HRESULT CGrayscale::GetInputStreamInfo(DWORD dwInputStreamID, MFT_INPUT_STREAM_INFO *pStreamInfo)
{
   
   
    AutoLock lock(m_critSec);
    if (pStreamInfo == NULL)
        return E_POINTER;
    
    if (!IsValidInputStream(dwInputStreamID))
        return MF_E_INVALIDSTREAMNUMBER;

    // NOTE: This method should succeed even when there is no media type on the stream. 
    //       If there is no media type, we only need to fill in the dwFlags member of 
    //       MFT_INPUT_STREAM_INFO. The other members depend on having a valid media type.
    pStreamInfo->hnsMaxLatency = 0;
    pStreamInfo->dwFlags = MFT_INPUT_STREAM_WHOLE_SAMPLES | MFT_INPUT_STREAM_SINGLE_SAMPLE_PER_BUFFER ;

    if (m_pInputType == NULL)