The difference between file:// and http:// for H5 page fetching camera

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title></title>
</head>
<body>
  <video id="video" width="480" height="320" controls>
  </video>
  <div>
    <button id="capture"></button>
  </div>
  <canvas id="canvas" width="480" height="320"></canvas>
  <script>
    //
    function getUserMedia(constraints, success, error) {
      if (navigator.mediaDevices.getUserMedia) {
        //API
        navigator.mediaDevices.getUserMedia(constraints).then(success).catch(error);
      } else if (navigator.webkitGetUserMedia) {
        //webkit
        navigator.webkitGetUserMedia(constraints,success, error)
      } else if (navigator.mozGetUserMedia) {
        //firfox
        navigator.mozGetUserMedia(constraints, success, error);
      } else if (navigator.getUserMedia) {
        //API
        navigator.getUserMedia(constraints, success, error);
      }
    }

    let video = document.getElementById("video");
    let canvas = document.getElementById("canvas");
    let context = canvas.getContext("2d");

    function success(stream) {
      //webkit
      let CompatibleURL = window.URL || window.webkitURL;
      //video
      console.log(stream);

      //video.src = CompatibleURL.createObjectURL(stream);
      video.srcObject = stream;
      video.play();
    }

    function error(error) {
      console.log(`${error.name}, ${error.message}`);
    }

    if (navigator.mediaDevices.getUserMedia || navigator.getUserMedia || navigator.webkitGetUserMedia || navigator.mozGetUserMedia) {
      //, 
      getUserMedia({video : {width: 480, height: 320}}, success, error);
    } else {
      alert("");
    }

    document.getElementById("capture").addEventListener("click", function () {
      context.drawImage(video, 0, 0, 480, 320);      
    })
  </script>
</body>
</html>

when I open the file://
prompt

directly when I save as html, it is OK to allow (the chrome under PC has a hint, the prompt box does not appear under safari, and neither safari, Wechat nor chrome pops up on the mobile phone), what can I do?