ILMVUserCallback Interface

The ILMVUserCallback interface is a user-defined interface. It must be registered by calling the put_ReceiveProcObj method of the ILMVCallback interface. This interface has one method.

Interface Methods:

HRESULT ReceiveProc (long pData, long lWidth, long lHeight, long lBitCount, long lSize, long bTopDown)

Parameters

pData A valid pointer to the frame data, passed in a long variable.
lWidth Width of the frame.
lHeight Height of the frame.
lBitCount Bits per pixel of the frame.
lSize Size of the frame buffer, in bytes.
bTopDown Value that indicates whether the image in the passed buffer (pData) is top-down (1) or bottom-up (0).

Description

This method is called for each frame received by the Video Callback Filter. The user can modify each frame by making changes to the frame's data. Please note that the memory for each frame is owned by the callback filter. If you wish to keep the frame data, you must make a copy of it. The user callback can dictate if this frame should continue to be used after the callback via the user callback function return code.

Return

After working on the frame data, this function can return one of the following values:

Value Meaning
VDCALBK_ERR_OK Success. The filter continues normally, delivering the processed frame.
VDCALBK_ERR_DROP Do not deliver the frame. The filter drops the frame and continues normally with the next frame in the stream.
VDCALBK_ERR_DELIVERLASTFRAME Deliver the previous frame (the last one delivered). The filter saves the last frame it delivers downstream, in case the same frame is needed more than once.

Note for C/C++ users: you can simply cast pData to a pointer to unsigned char.

Note for .NET users: For more examples on how to use the frame data in .NET applications, look at the sample code from ILMAUserCallback2 Interface.

Note for .NET users: These callbacks are implemented in .NET as a function without a return value. In order to be able to return a value other than VDCALBK_ERR_OK from your app, you need to throw an HRESULT exception before returning from ReceiveProc. One way to do this is as shown in the following example:

public class ReturnValueException : Exception 
{ 
   public ReturnValueException(object HResultValue) 
   { 
      HResult = (int)HResultValue; 
   } 
} 
public class LEADCallbackPlay : LMVCallbackLib.ILMVUserCallback 
{ 
   public void ReceiveProc(int pData, int lWidth, int lHeight, int lBitCount, int lSize, int bTopDown) 
   { 
      ' you need to throw an error only if you want to return anything other that VDCALBK_ERR_OK 
      ' throw new ReturnValueException(LMVCallbackLib.VdCalBkErrConstants.VDCALBK_ERR_DROP); 
   } 
} 

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