To stop HTML5 videos from playing in a Webflow modal when it is closed, you need to ensure that video playback is paused or reset when the modal is closed.
```javascript
document.querySelector('.modal-close-btn').addEventListener('click', function() {
var video = document.querySelector('.video-element');
video.pause();
video.currentTime = 0; // Resets the video to the beginning
});
```
.modal-close-btn and .video-element with your specific modal close button and video element identifiers.
To stop videos from playing when a modal is closed in Webflow, integrate a custom JavaScript script that listens for the modal close event and pauses and resets the video. By doing so, you ensure that videos do not continue to play in the background, providing a better user experience.