How to Auto-Play videos on scroll

Table of content

• Using IntersectionObserver
• Understanding the Configuration
• The example

This week, I had a user story to add a video mode to a card that displays some content. One of the acceptance criteria was that the video must start playing when the user scrolls down, and the card reaches the center of the screen.

It turned out to be simpler than I expected. Here’s how you can do it too.

Using IntersectionObserver

To detect if an element intersects with another (including the viewport), you can use an IntersectionObserver like this:

  
    const observer = new IntersectionObserver((entries) => {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                entry.target.play();  // Start video playback
            } else {
                entry.target.pause(); // Pause video when out of view
            }
        });
    }, {
        root: document.querySelector("#scrollArea"),
        rootMargin: "0px",
        threshold: 0.5
    });

    observer.observe(document.querySelector(".video-card video"));
  

Understanding the Configuration

• root: This defines the ancestor of the target element. If set to null, it defaults to the viewport.
• rootMargin: Adjusts the margin around the root. Should be adapted for desktop and mobile devices.
• threshold: A value between 0 and 1 that represents the percentage of visibility required to trigger the observer's callback. In this case, 1.0 means the entire element must be in view.

The example

In my case, as I wanted the card to start reproducing the video only while its in the center (on mobile), I had to adjust the rootMargin property like so:

  
    ...
    rootMargin: "-35% 0px -35% 0px",
    ...
  

With this setup, only one card at a time will play its video when it's centered on the screen. 🎥✨

Full code:

  
      document.addEventListener('DOMContentLoaded', () => {
        const videos = document.querySelectorAll('video');

        const options = {
          root: null,
          rootMargin: '-35% 0px -35% 0px',
          threshold: 0.5
        };

        const observer = new IntersectionObserver((entries, observer) => {
          entries.forEach(entry => {
            const video = entry.target;
            if (entry.isIntersecting) {
              video.play();
            } else {
              video.pause();
            }
          });
        }, options);

        videos.forEach(video => {
          observer.observe(video);
        });
      });
  

I hope you have learned something new from all. If you think this might help other people, please hit the like button so that others can read it. ❤️

If you have any thoughts or questions, feel free to leave a comment!