How data is moving across filters through pins in OBS-Studio virtual camera on windows?

Question

I liked OBS-Studio's virtual camera feature.

I tried to understand its working but could not understand properly. I only understood that it is built using DirectShow. Project contains OutputFilter, OutputPin, CaptureFilter and CapturePin

class OutputFilter : public IBaseFilter {
    // ...
    friend class OutputPin;
    IFilterGraph *graph;
    ComPtr<OutputPin> pin;
    // ...
}

class OutputPin : public IPin, public IAMStreamConfig, public IKsPropertySet {
    // ...
    friend class OutputFilter;
    // ...
}

class CaptureFilter : public IBaseFilter {
    // ...
    friend class CapturePin;
    ComPtr<IFilterGraph> graph;
    ComPtr<CapturePin> pin;
    // ...
}

class CapturePin : public IPin, public IMemInputPin {
    // ...
    CaptureFilter *filter;
    // ...
}

How data is moving across these filters and pins when we are enabling virtual camera?

Answer 1

They are using a shared memory server. Basically, they have a rendering filter that copies the incoming bitmaps into the shared memory. And then they have a capture filter that reads the bitmaps from the shared memory. You can see some of their code here: win-dshow