Piik/native/capture/windows

Windows Capture Process

This isolated Windows process is the capture candidate for Screener Client. It enumerates local displays and visible top-level windows, binds each window to its PID and process creation time, and has independent modes for:

• capability discovery (--probe);
• process-tree or default-device loopback PCM (--capture-audio); or
• WGC/D3D11 screen/window video with adapter-bound Media Foundation H.264 or libvpx VP8 output (--capture-video --codec auto|h264|vp8).
• bounded 320x180 BMP source previews (--preview), delivered once per target over the local control connection rather than the media route.

The video command receives the current product resolution, frame-rate, bitrate, and quality preference. A replacement process applies live changes while the Go session retains its Pion source and connections.

Video and audio run as separate bounded child processes. A source whose audio loopback cannot be initialized keeps video available and reports audio unavailable instead of failing the whole source. Process loopback is probed by activation rather than inferred from a Windows build number; display sources use the standard render-device loopback available on Windows 10 and later.

Auto compares target-profile encoding work within a four-second selection budget; H.264 that meets the target needs no software comparison. The selected codec remains fixed across profile and source changes. VP8 reads the existing NV12 surface through one staging texture and uses the same encoded-frame boundary. The process has no network fallback. The Client consumes the selected process or system-audio stream through its native media edge when the capability probe reports support. Build it outside the repository for a bounded capability run:

npm run check:client-capture

The implementation follows Microsoft's MIT-licensed reference samples and official API contracts without copying their WIL framework. The retained MF fixture compiles the same encoder source with SCREENER_H264_FIXTURE; there is not a second product MFT implementation. The build caches pinned libvpx, NASM and make inputs under build/client-check; only statically linked VP8 code and its notices enter the package.

• https://github.com/microsoft/Windows-classic-samples/tree/main/Samples/ApplicationLoopback
• https://github.com/microsoft/Windows.UI.Composition-Win32-Samples/tree/master/cpp/ScreenCaptureforHWND
• https://learn.microsoft.com/en-us/windows/win32/api/audioclientactivationparams/ns-audioclientactivationparams-audioclient_activation_params
• https://learn.microsoft.com/en-us/windows/uwp/audio-video-camera/screen-capture
• https://learn.microsoft.com/en-us/windows/win32/api/windows.graphics.capture.interop/nf-windows-graphics-capture-interop-igraphicscaptureiteminterop-createforwindow
• https://learn.microsoft.com/en-us/uwp/api/windows.graphics.capture.direct3d11captureframepool.createfreethreaded