Capture Screen Contents

Get the user's media access status
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todesktop.systemPreferences.getMediaAccessStatus(
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    'screen'
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);
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This will return a Promise which will resolve to not-determined, granted, denied, restricted or unknown
On Windows and macOS 10.14 Mojave or lower the response will always begranted . macOS 10.15 Catalina or higher requires consent for screen access. 
To get that consent just run the code below, it will automatically ask for permission
Get the user's screen sources
Say we wanted to get a user's screens and windows
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const sources = await todesktop.desktopCapturer.getSources({
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    types: ["window", "screen"],
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    thumbnailSize: {
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      height: 720,
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      width: 1000,
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    },
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});
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This will return an array of sources
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[
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    {
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        appIcon: null,
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        display_id: "",
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        id: "window:60230:0",
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        name: "Developer Tools - http://localhost:3000/",
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        thumbnail: "data:image/png;base64,iV..."
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    },
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    ...
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]
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Getting a source id
You'll need a way of choosing which screen/window to capture. Unlike in a browser, your Desktop app will need to implement its own UI for this.
For example if you wanted to reproduce a browsers selection feature you could loop through the sources and listen to click events on each.
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<div id="desktop-capturer-sources"></div>
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​
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<button id="get-sources">Get Sources</button>
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​
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<style>
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  #desktop-capturer-sources {
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    display: flex;
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    width: 60%;
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    height: 400px;
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    background-color: white;
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    box-shadow: #c4c4c4 2px 4px 5px 2px;
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    flex-wrap: wrap;
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    overflow: auto;
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    justify-content: center;
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  }
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​
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  .desktop-source {
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    min-width: 30%;
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    padding: 1rem;
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    margin: 0.25rem;
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  }
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​
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  .desktop-source > img {
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    width: 250px;
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  }
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</style>
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​
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<script>
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  window.onload = () => {
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    document
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      .getElementById("get-sources")
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      .addEventListener("click", () => getSources());
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  };
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​
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  const getSources = async () => {
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    const sources = await ...;
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    const container = document.getElementById("desktop-capturer-sources");
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    sources.forEach((source) => {
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      const el = document.createElement("div");
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      el.className = "desktop-source";
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      const img = document.createElement("img");
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      img.src = source.thumbnail;
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      el.appendChild(img);
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      // We'll create the getStream func later
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      el.addEventListener("click", () => getStream(source.id));
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      container.appendChild(el);
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    });
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  };
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</script>
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This will give you something like:
Getting Screens / Windows in Desktop App
Get the stream to a source
After choosing a source we'll use its id and  navigator.mediaDevices.getUserMedia to get the stream.
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const getStream = async (id) => {
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  let stream = await navigator.mediaDevices.getUserMedia({
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    audio: false,
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    video: {
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      mandatory: {
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        chromeMediaSource: "desktop",
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        chromeMediaSourceId: id,
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        minWidth: 1280,
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        maxWidth: 1280,
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        minHeight: 720,
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        maxHeight: 720,
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      },
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    },
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  });
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}
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Play the stream
If you have a <video> in your HTML you can then use
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const video = document.querySelector("video");
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video.srcObject = stream;
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video.onloadedmetadata = (e) => video.play();
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API Reference
todesktop.desktopCapturer.getSources
Exposes the destopCapturer.getSources electron API: https://www.electronjs.org/docs/api/desktop-capturer​
Accepts an options object:
types String[] - The types of desktop sources to be captured, eitherscreen or window.
thumbnailSize {width: number, height: number} (optional) - Default is 150 x 150.
fetchWindowIcons Boolean (optional) - Default value is false
Returns a Promise which resolves into an array of DesktopCapturerSource objects each having:
id String - The id of a window or screen that can be used as a chromeMediaSourceId later
name String - The name of the screen (Entire Screen or Screen <index>) or the window's title
thumbnail String - A data Url of the image
display_id String - A unique identifier that will correspond to the id property
appIcon String - A data Url of the app Icon or null if type is screen
​

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Contents

Get the user's screen sources

Getting a source id

Get the stream to a source

Play the stream

API Reference

todesktop.desktopCapturer.getSources