Browser webcam hello world

Just below this paragraph, you can see yourself! In this post I show how webpages can access the webcam, then stream it to a <video> element.

Here’s the code that achieves this:

<!-- First, a video element to stream the webcam to ... -->
<video id="webcam" width="400"></video>

// ... then some JavaScript to access the webcam stream 
// and attach it to the video element.
const vidEl = document.getElementById("webcam");
navigator.mediaDevices.getUserMedia({ video: { facingMode: "user" } })
  .then(stream => {
    vidEl.srcObject = stream;
    vidEl.play();
  })
  .catch((err) => console.log("error getting webcam", err));

When this page loaded, it prompted you for permission to access your webcam. This happened when the page called navigator.mediaDevices.getUserMedia(...), which returns a Promise<MediaStream>. When you respond to the permission request, the promise resolves (or rejects, if you deny permission).

The <video> element, as an HTMLMediaElement, has a srcObject property which can be any MediaStream. By assigning the webcam stream to the <video> element’s input, we display the webcam.

Finally, to start using the source, you must call .play() on the <video> element.

Tagged #programming. All content copyright James Fisher 2019. This post is not associated with my employer. Found an error? Edit this page.