ScreenCapturer

老猫10/22/22About 1 min

ScreenCapturer

Live screen capture session created by requestScreenCapture. Yields successive Image frames from the virtual display.

Inheritance

EventEmitter
↳ ScreenCapturer

ScreenCapturer extends EventEmitter, so you can use on / once / off etc.

Events

image_available

▸ on(event, listener): this

Fires whenever a new frame is available (same moment you could read via latestImageOrNull).

Example

"nodejs";
const { requestScreenCapture } = require("media_projection");

async function main() {
  const capturer = await requestScreenCapture();

  capturer.on("image_available", () => {
    console.log("New frame available");
    const img = capturer.latestImageOrNull();
    if (img) {
      console.log("Size:", img.width, "x", img.height);
    }
  });

  $autojs.keepRunning();
}
main();

Parameters

Name	Type	Description
`event`	`"image_available"`	Fixed event name.
`listener`	() => `void`	Called when a new frame is ready.

Returns

this

The capturer instance (chainable).

Methods

latestImage

▸ latestImage(): Image

Returns the most recent frame. Throws ImageUnavailableError if none exists yet.

Example

"nodejs";
const { requestScreenCapture } = require("media_projection");

async function main() {
  const capturer = await requestScreenCapture();

  await capturer.awaitForImageAvailable();

  const img = capturer.latestImage();
  console.log("Size:", img.width, "x", img.height);

  capturer.stop();
}
main();

Throws

ImageUnavailableError when no frame is available.

latestImageOrNull

▸ latestImageOrNull(): Image | null

Same as latestImage, but returns null instead of throwing when no frame exists.

Example

"nodejs";
const { requestScreenCapture } = require("media_projection");

async function main() {
  const capturer = await requestScreenCapture();

  const img = capturer.latestImageOrNull();
  if (img) {
    console.log("Size:", img.width, "x", img.height);
  } else {
    console.log("No frame yet");
  }

  capturer.stop();
}
main();

Returns

Image | null

Latest frame, or null.

nextImage

▸ nextImage(): Promise<Image>

Waits until the next frame is produced and resolves with it.

Example

"nodejs";
const { requestScreenCapture } = require("media_projection");

async function main() {
  const capturer = await requestScreenCapture();

  const img = await capturer.nextImage();
  console.log("First frame:", img.width, "x", img.height);

  const img2 = await capturer.nextImage();
  console.log("Second frame:", img2.width, "x", img2.height);

  capturer.stop();
}
main();

Returns

Promise<Image>

Promise that resolves with the next frame.

awaitForImageAvailable

▸ awaitForImageAvailable(): Promise<void>

Resolves when at least one frame exists. Right after permission is granted, the pipeline may need a moment before the first frame arrives; this helper waits for that. If a frame is already available, it resolves immediately.

Example

"nodejs";
const { requestScreenCapture } = require("media_projection");

async function main() {
  const capturer = await requestScreenCapture();

  await capturer.awaitForImageAvailable();
  console.log("First frame ready");

  const img = capturer.latestImage();
  console.log("Size:", img.width, "x", img.height);

  capturer.stop();
}
main();

Returns

Promise<void>

stop

▸ stop(): void

Tear down capture and stop emitting frames.

Example

"nodejs";
const { requestScreenCapture } = require("media_projection");

async function main() {
  const capturer = await requestScreenCapture();

  for (let i = 0; i < 5; i++) {
    const img = await capturer.nextImage();
    console.log(`Frame ${i + 1}`);
  }

  capturer.stop();
  console.log("Capture stopped");
}
main();

Returns

void