webrtc-java

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Window Capturer ​

The WindowCapturer enumerates and captures individual application windows. Use it to list open windows and to drive window-source selection for desktop capture workflows.

API: dev.onvoid.webrtc.media.video.desktop.WindowCapturer

Overview ​

  • Purpose: Discover and capture specific windows.
  • Pairs with: VideoDesktopSource to create a video source capturing the chosen window ID.
  • Common ops: list windows, select one, configure capture parameters, start capture via callback, or pass the window ID to VideoDesktopSource.
  • Resource management: Call dispose() when finished to free native resources.

Key methods (inherited from DesktopCapturer):

  • List<DesktopSource> getDesktopSources() – enumerate available windows
  • void selectSource(DesktopSource source) – choose which window to capture
  • void setFocusSelectedSource(boolean focus) – attempt to focus/raise the selected window
  • void setMaxFrameRate(int maxFrameRate) – limit the capture frame rate
  • void start(DesktopCaptureCallback callback) – start capture, frames via callback
  • void captureFrame() – request a single capture
  • void dispose() – release resources

Typical usage: enumerate windows ​

java
import dev.onvoid.webrtc.media.video.desktop.DesktopSource;
import dev.onvoid.webrtc.media.video.desktop.WindowCapturer;
import java.util.List;

WindowCapturer windowCapturer = new WindowCapturer();
try {
    List<DesktopSource> windows = windowCapturer.getDesktopSources();
    for (DesktopSource w : windows) {
        System.out.printf("Window: %s (ID: %d)%n", w.title, w.id);
    }
}
finally {
    windowCapturer.dispose();
}

Selecting a window and starting capture with a callback ​

java
import dev.onvoid.webrtc.media.video.desktop.*;
import dev.onvoid.webrtc.media.video.VideoFrame;

WindowCapturer capturer = new WindowCapturer();
try {
    DesktopSource window = capturer.getDesktopSources().stream().findFirst()
        .orElseThrow(() -> new IllegalStateException("No windows found"));

    capturer.selectSource(window);
    capturer.setMaxFrameRate(30);
    capturer.setFocusSelectedSource(true); // optional

    DesktopCaptureCallback callback = (result, frame) -> {
        if (result == DesktopCapturer.Result.SUCCESS && frame != null) {
            // process VideoFrame for the selected window
        }
    };

    capturer.start(callback);
    capturer.captureFrame();
}
finally {
    capturer.dispose();
}

Using with VideoDesktopSource to create a VideoTrack ​

java
import dev.onvoid.webrtc.media.video.VideoDesktopSource;
import dev.onvoid.webrtc.media.video.desktop.*;

WindowCapturer wc = new WindowCapturer();
DesktopSource window = wc.getDesktopSources().get(0);

VideoDesktopSource vds = new VideoDesktopSource();
vds.setFrameRate(30);
vds.setMaxFrameSize(1280, 720);

// Select the window (isWindow = true)
vds.setSourceId(window.id, true);

vds.start();

// ...

vds.stop();
vds.dispose();
wc.dispose();

Integration tips ​

  • Window availability is dynamic; refresh getDesktopSources() if the set of open windows changes.
  • Not all OSes allow focusing/raising another app’s window; setFocusSelectedSource behavior may vary by platform.
  • If the window is minimized or occluded, the captured content may be affected depending on platform.