NSFW communities are often a mixture of redgifs videos (which play automatically) and <video> elements linking to mp4s which don’t. This script evens the playing field so mp4 videos autoplay as well. Hover your mouse over the video and it’ll unmute.

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

  const observer = new IntersectionObserver((entries) => {  
    entries.forEach(entry => {  
      if (entry.isIntersecting) {  
        entry.target.play().catch(err => {  
          console.warn("Autoplay blocked:", err);  
        });  
      } else {  
        entry.target.pause();  
      }  
    });  
  }, { threshold: 0.5 });  

  videos.forEach(video => {  
    video.muted = true; // ensure muted initially  
    observer.observe(video);  

    video.addEventListener("mouseenter", () => {  
      video.muted = false; // unmute on hover  
    });  

    video.addEventListener("mouseleave", () => {  
      video.muted = true; // re-mute when not hovered  
    });  
  });  
});  

Put it into the ‘Additional JS’ field in /admin/misc.