切换前置罕见摄像头时，HTML5 视频元素请求将永远处于待处理状态(在移动设备上的 chrome 上) [英] HTML5 video element request stay pending forever (on chrome in mobile) when toggle over front-rare camera

问题描述

我正在开发一款应用，让用户可以使用前置/稀有摄像头拍摄照片.它工作得很好，但是当切换相机前/罕见 var playPromise = videoStream.play() 时，它处于挂起状态.有时承诺得到解决，相机有时不工作.

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此问题仅在 chrome 浏览器中出现，在 mozila 和 firefox 中没有

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 试试 {停止网络摄像头()；//切换相机时停止媒体流流 = 等待 navigator.mediaDevices.getUserMedia({video: true});/* 使用流 */让 videoStream = document.getElementById('captureCandidateId');videoStream.srcObject = 流；//videoStream.play();var playPromise = videoStream.play();如果(播放承诺！== 未定义){playPromise.then(_ => {//自动播放开始！//显示正在播放的 UI.}).catch(错误=> {//自动播放被阻止//显示暂停的 UI.});}};} 抓住(错误){/* 处理错误 */console.log(err.name + ": " + err.message);}

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 let stopWebCam = function (pictureType) {setTimeout(()=>{让 videoStream = document.getElementById('captureCandidateId');const 流 = videoStream.srcObject;如果(流&&stream.getTracks){const track = stream.getTracks();轨道.forEach(功能(轨道){track.stop();});}videoStream.srcObject = null;}, 0)}

解决方案

在这里，我为你起草了一段代码，这比你想要做的更简单、更小.我只是从视频元素中获取流并将其绘制到画布上.图片可以右键下载.注意:示例在 StackOverflow 中不起作用

如果你愿意，你也可以根据自己的需要进行一些编辑，比如:

1. 选择要使用的相机
2. 隐藏视频流
3. 添加一种更简单的方法在您的设备上下载照片
4. 如果您有照片，您还可以添加将照片直接上传到服务器的功能

I'm developing an app where users can capture photo using a front/rare camera. it working perfectly but when toggle over camera front/rare var playPromise = videoStream.play() is gone in pending state. some times promise get resolve, the camera is working sometimes not.

this issue occurs only in chrome browser not in mozila and firefox

       try {
            stopWebCam(); // stop media stream when toggle over camera
            stream = await navigator.mediaDevices.getUserMedia({video: true});
            /* use the stream */
            let videoStream = document.getElementById('captureCandidateId');
            videoStream.srcObject = stream;

                // videoStream.play();
                var playPromise = videoStream.play();

                if (playPromise !== undefined) {
                  playPromise.then(_ => {
                    // Automatic playback started!
                    // Show playing UI.
                                 
                  })
                  .catch(error => {
                    // Auto-play was prevented
                    // Show paused UI.
                  });
                }

                                };
        } catch(err) {
            /* handle the error */
            
            console.log(err.name + ": " + err.message);
        }

    let stopWebCam = function (pictureType) {

    setTimeout(()=>{
        let videoStream = document.getElementById('captureCandidateId');
        const stream = videoStream.srcObject;
        if (stream && stream.getTracks) {
            const tracks = stream.getTracks();
            tracks.forEach(function(track) {
                track.stop();
            });
        }
        videoStream.srcObject = null;
      }, 0)
    }

解决方案

Here, I drafted a piece of code for you, this is much more simple and smaller approach than what you are trying to do. I am just taking the stream from the video element and drawing it to canvas. Image can be downloaded by right clicking. NOTE: Example does not work in StackOverflow

<video id="player" controls autoplay></video>
<button id="capture">Capture</button>
<canvas id="canvas" width=320 height=240></canvas>
<script>
  const player = document.getElementById('player');
  const canvas = document.getElementById('canvas');
  const context = canvas.getContext('2d');
  const captureButton = document.getElementById('capture');

  const constraints = {
    video: true,
  };

  captureButton.addEventListener('click', () => {
    // Draw the video frame to the canvas.
    context.drawImage(player, 0, 0, canvas.width, canvas.height);
  });

  // Attach the video stream to the video element and autoplay.
  navigator.mediaDevices.getUserMedia(constraints)
    .then((stream) => {
      player.srcObject = stream;
    });
</script>

If you want, you can also make some edits according to your needs, like:

1. Choose which camera to use
2. Hide the video stream
3. Add a easier method to download the photo on your device
4. You can also add a functionality to upload the photo straight to the server if you have one

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