ReactJS: How to play video which comes in center and pause all other videos

Question

In maplist I have 20 items that is 20 videos I want to do is play video which comes in center of viewport and pause all others and keep that behaviour throughout scrolling:

const [reels, setReels] = useState([]);
useEffect(() => {
  fetchAllVideos();
}, []);

const fetchAllVideos = async () => {
  const getAllVideosRes = await getAllVideos(pageNumber);
  setReels(getAllVideosRes);
};

return (
  <>
  reels.map((item, idx) => {
  return (
    <MDBox mb={3} key={idx}>
      <Card sx={{ borderRadius: "25px" }}>
        <video style={{ height: "100%", width: "100%", objectFit: "cover", borderRadius: "25px", }} loop controls>
          <source src={item.photo} type="video/mp4" />
        </video>
    </MDBox>
  </Card>
  </MDBox >
  );
  })

</>
)

Answer 1

Use an intersectionObserver to track the items as they enter or leave the container.

Set the threshold to be 100% of the element (threshold: 1), and the rootMargin to limit the intersection area to the center of the container (rootMargin: '-20% 0% -20% 0%').

const { useRef, useState, useEffect, useCallback } = React

const usePlayIntersection = () => { 
  const containerRef = useRef();
  const [observer, setObserver] = useState();

  useEffect(() => {
    const cb = entries => {
      entries.forEach(({ isIntersecting, target, intersectionRect }) => {
        if(isIntersecting) target.play()
        else target.pause()
      })
    };
  
    const obs = new IntersectionObserver(cb, {
      root: containerRef.current,
      rootMargin: '-20% 0% -20% 0%',
      threshold: 1
    })
    
    setObserver(obs)
  
    return () => {
      obs.disconnect()
    }
  }, [])
  
  const observe = useCallback(el => {
    if(observer) observer.observe(el)
  }, [observer])
  
  return [observe, containerRef]
}

const Demo = ({ videos }) => {
  const [observe, containerRef] = usePlayIntersection();
  
  return (
    <div className="container" ref={containerRef}>
      <div className="filler" />
      {videos.map(vid => (
        <video 
          ref={observe}
          muted
          key={vid}
          loop controls>
        <source src={vid} type="video/mp4" />
      </video>
      ))}
      <div className="filler" />
    </div>
  )
}

const videos = ["http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4","http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/ElephantsDream.mp4","http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/VolkswagenGTIReview.mp4","http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/WeAreGoingOnBullrun.mp4","http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/WhatCarCanYouGetForAGrand.mp4"]

ReactDOM
  .createRoot(root)
  .render(<Demo videos={videos} />)

html, body {
  margin: 0;
  padding: 0;
}

.container {
  height: 100vh;
  overflow: auto;
}

video, .filler {
  display: block;
  margin: 1em;
  height: 40%; 
  width: 40%;
  objectFit: cover;
  borderRadius: 25px;
}

<script crossorigin src="https://unpkg.com/react@18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@18/umd/react-dom.development.js"></script>

<div id="root"></div>