Publishing Point with Screen Capture Source

This use-case demonstrates how to capture the desktop screen or a specific application window, encode it as H.264 video, and serve it as a publishing point. The IScreenCaptureSource supports both full-screen and per-window capture modes.

Overview

The createScreenCaptureSource() method is an async void method that performs the following:

Enumerates available displays
Creates a screen capture source via SourceFactory
Configures either full-screen or window capture mode
Sets the desired H.264 encoding parameters
Creates the publishing point

The method is called from a background task on supported platforms:

if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
    || RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
{
    Task.Run(() => this.createScreenCaptureSource());
}

Enumerating Displays

var display = VAST.Capture.DisplayHelper.EnumerateDisplays()[0];

DisplayHelper returns a list of available displays with their device IDs and screen coordinates. The sample uses the first display.

Creating the Source

VAST.Capture.IScreenCaptureSource source = VAST.Media.SourceFactory.CreateScreenCapture();

Full-Screen Capture

source.DeviceId = display.DeviceId;
source.Region = new VAST.Common.Rect
{
    Left = display.Location.Left,
    Top = display.Location.Top,
    Right = display.Location.Right,
    Bottom = display.Location.Bottom
};
source.ShowMouse = true;

Set the DeviceId to the target display and Region to the display's full area. ShowMouse controls whether the mouse cursor is included in the capture.

Window Capture

var window = VAST.Capture.DisplayHelper.FindWindow(display.DeviceId, "VLC")[0];
source.WindowHandle = window;
source.WindowCaptureMode = VAST.Capture.WindowCaptureMode.Resize;
source.ShowMouse = true;

To capture a specific window, use DisplayHelper.FindWindow to locate it by title. Set WindowHandle to the found window handle and WindowCaptureMode to control how the capture adapts when the window is resized.

IScreenCaptureSource Properties

Property	Type	Description
`DeviceId`	`string`	Display device ID (for full-screen capture)
`Region`	`Rect`	Screen region to capture (left, top, right, bottom)
`WindowHandle`	`IntPtr`	Window handle (for window capture)
`WindowCaptureMode`	`WindowCaptureMode`	How to handle window resizing
`ShowMouse`	`bool`	Include the mouse cursor in the capture

Configuring Encoding

int width = 1280;
int height = 720;
VAST.Common.Rational framerate = new VAST.Common.Rational(30);

VAST.Common.MediaType mt = new VAST.Common.MediaType
{
    ContentType = VAST.Common.ContentType.Video,
    CodecId = VAST.Common.Codec.H264,
    Bitrate = width * height * 3,
    Width = width,
    Height = height,
    Framerate = framerate,
};
mt.Metadata.Add("KeyframeInterval", "30");
mt.Metadata.Add("Profile", "66");

await source.SetDesiredOutputType(0, mt);

The captured screen content is scaled to 1280x720 and encoded as H.264 at 30 fps with Baseline profile. The Bitrate is calculated from the output dimensions. By default, the built-in framework is used for encoding. To use FFmpeg instead:

source.EncoderParameters = new VAST.Media.EncoderParameters
{
    PreferredMediaFramework = VAST.Common.MediaFramework.FFmpeg,
    AllowHardwareAcceleration = false,
};

Creating the Publishing Point

this.server.CreatePublishingPoint("screen", source);

The screen capture stream is video-only. It is available at rtsp://server/screen, rtmp://server/live/screen, http://server:8888/hls/screen, etc.

Error Handling

The method is wrapped in a try/catch block. If the capture library is not available on the system, the exception is caught and the publishing point is not created. The source is disposed in the finally block if the publishing point was not successfully created.

Platform Support

Screen capture is supported on Windows and Linux. The sample guards the call with a platform check before invoking createScreenCaptureSource().

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