videofilt_vdxframe_creatingavideofilter

VirtualDub Plugin SDK 1.2

Creating a filter

Once you have the entry point in place, you can begin writing the video filters themselves.

Deriving from VDXVideoFilter

To create a video filter, first derive from the VDXVideoFilter base class to produce the derived class for your filter. There are two methods on the wrapper base class that must be overridden, GetParams() and Run(). These correspond to the paramProc and runProc entry points, respectively. Therefore, this is the minimal filter implementation:

#include <vd2/VDXFrame/VideoFilter.h>

class EmptyFilter : public VDXVideoFilter {
public:
    virtual uint32 GetParams();
    virtual void Run();
};

uint32 EmptyFilter::GetParams() {
    return FILTERPARAM_SWAP_BUFFERS;
}

void EmptyFilter::Run() {
}

The VDXVideoFilter class contains protected fields called fa and ff that correspond to the filter activation and functions structures traditionally passed to the filter entry points. This avoids having to declare them on every method and allows code written to use those variables to port directly over to the wrappers.

Other entry points in the video filter API are also exposed in the VideoFilter base class, and can be implemented as simply as overloading the appropriate base class method. The base class methods are sometimes simplified — for instance, both the stringProc and stringProc2 API methods can be implemented by overloading VDXVideoFilter::GetSettingsString().

Creating the video filter definition structure

Once you have the video filter class in place, the video filter definition can be created using the VDXVideoFilterDefinition template:

extern VDXFilterDefinition filterDef_emptyFilter =
    VDXVideoFilterDefinition<EmptyFilter>(
        "My Name",
        "Sample: Empty Filter",
        "Sample filter from the VirtualDub Plugin SDK: Does nothing");

The three arguments to the constructor are author, name, and description. All other fields are derived from the filter class.

That's it — you should now have a working video filter.