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Data Input and Output

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[The feature associated with this page, Windows Media Player SDK, is a legacy feature. It has been superseded by MediaPlayer. MediaPlayer has been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer instead of Windows Media Player SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

Windows Media Player provides audio or video data to DSP plug-ins through an input buffer allocated by Windows Media Player. DSP plug-ins return processed data to Windows Media Player through an output buffer that is also allocated by Windows Media Player. Windows Media Player manages the process of passing data between itself and the DSP plug-in by calling methods implemented by the plug-in. For a plug-in acting as a DirectX Media Object (DMO), the process works as follows:

  1. Windows Media Player calls IMediaObject::ProcessInput, passing a pointer to an IMediaBuffer object to the DSP plug-in.
  2. The DSP plug-in keeps a reference count on the input buffer object. The DSP plug-in returns an appropriate success or failure HRESULT.
  3. Windows Media Player calls IMediaObject::ProcessOutput, passing a pointer to an array of DMO_OUTPUT_DATA_BUFFER structures (which contain output buffers) to the DSP plug-in.
  4. The DSP plug-in processes the data in the input buffer and then copies the data to the appropriate output buffer. The DSP plug-in releases the reference count on the input buffer object when all the data in the buffer has been processed. The DSP plug-in then returns an appropriate success or failure HRESULT.
  5. Windows Media Player renders the content in the output buffer.

For a plug-in acting as a Media Foundation Transform (MFT), the process works as follows:

  • Windows Media Player calls IMFTransform::ProcessInput, passing a pointer to an IMFSample interface object to the DSP plug-in.
    1. The DSP plug-in keeps a reference count on the IMFSample interface. The DSP plug-in returns an appropriate success or failure HRESULT.
    2. Windows Media Player calls IMFTransform::ProcessOutput, passing a pointer to an array of MFT_OUTPUT_DATA_BUFFER structures (which contain output buffers) to the DSP plug-in.
    3. The DSP plug-in processes the data in the input buffer and then copies the data to the appropriate output buffer. The DSP plug-in releases the reference count on the input buffer object when all the data in the buffer has been processed. The DSP plug-in then returns an appropriate success or failure HRESULT.
    4. Windows Media Player renders the content in the output buffer.

This process repeats continuously while the plug-in is enabled and Windows Media Player has content to render.

Note

Do not write code that writes data to the input buffer or reads data from the output buffer. Incorrectly accessing data buffers may yield unexpected results.

 

DSP Plug-in Developer Overview