Fooling Around

Previously on the topic:

• Part 1: Starting the Project
• Part 2: Video Processing
• Part 3: Persistence, Automation and Property Pages
• Part 4: Merit

Due to the nature of the brightness and constract correction processing, it would make sense to combine and simplify processing to apply correction “in-place”, that is without copying data from input to output buffer, but instead processing the same buffer before it is passed further downstream.

DMO API offers additional optional IMediaObjectInPlace interface to be implemented on the DMO which the hosting object might prefer to regular IMediaObject.

The interface itself is simple with basically the only Process method to actually handle the processing:

// IMediaObjectInPlace
	STDMETHOD(Process)(ULONG nSize, BYTE* pnData, REFERENCE_TIME nStartTime, DWORD nFlags)
	STDMETHOD(Clone)(IMediaObjectInPlace** ppMediaObject)
	STDMETHOD(GetLatency)(REFERENCE_TIME* pnLatencyTime)

Still the interest in in-place processing in DMO is more abstract because current DMO Wrapper Filter implementation does not take advantage of in-place processing and chooses to always work through IMediaObject.

However if the object is hosted directly, in-place processing might make sense and be important.

To support in-place processing in the DMO it is required to inherit from interface and add it to the COM map:

class ATL_NO_VTABLE CBrightnessContrastObject :
	public CComObjectRootEx<CComMultiThreadModel>,
	...
	public IMediaObjectInPlace
...
BEGIN_COM_MAP(CBrightnessContrastObject)
	...
	COM_INTERFACE_ENTRY(IMediaObjectInPlace)
END_COM_MAP()

And implement the IMediaObjectInPlace methods, of which IMediaObjectInPlace::Process is the essential.

Source code: DmoBrightnessContrastSample.05.zip (note that Release build binary is included)