Edit

Share via

Step 2. Declare the Filter Class

  • Article

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

This is step 2 of the tutorial Writing Transform Filters.

Start by declaring a C++ class that inherits the base class:

class CRleFilter : public CTransformFilter
{
    /* Declarations will go here. */
};

Each of the filter classes has associated pin classes. Depending on the specific needs of your filter, you might need to override the pin classes. In the case of CTransformFilter, the pins delegate most of their work to the filter, so you probably don't need to override the pins.

You must generate a unique CLSID for the filter. You can use the Guidgen or Uuidgen utility; never copy an existing GUID. There are several ways to declare a CLSID. The following example uses the DEFINE_GUID macro:

[RleFilt.h]
// {1915C5C7-02AA-415f-890F-76D94C85AAF1}
DEFINE_GUID(CLSID_RLEFilter, 
0x1915c5c7, 0x2aa, 0x415f, 0x89, 0xf, 0x76, 0xd9, 0x4c, 0x85, 0xaa, 0xf1);

[RleFilt.cpp]
#include <initguid.h>
#include "RleFilt.h"

Next, write a constructor method for the filter:

CRleFilter::CRleFilter()
  : CTransformFilter(NAME("My RLE Encoder"), 0, CLSID_RLEFilter)
{ 
   /* Initialize any private variables here. */
}

Notice that one of the parameters to the CTransformFilter constructor is the CLSID defined earlier.

Next: Step 3. Support Media Type Negotiation.

Writing DirectShow Filters