Callback event for getUserMedia ()

Question

Callback event for getUserMedia ()

I am trying to take a picture from my webcam using the navigator.mediaDevices.getUserMedia()and functions canvas.getContext('2d').drawImage().

When I do it like this, it works fine:

function init(){
  myVideo = document.getElementById("myVideo") 
  myCanvas = document.getElementById("myCanvas");
  videoWidth = myCanvas.width;
  videoHeight = myCanvas.height;
    
  startVideoStream();
}

function startVideoStream(){
  navigator.mediaDevices.getUserMedia({audio: false, video: { width: videoWidth, height: videoHeight }}).then(function(stream) {
    myVideo.src = URL.createObjectURL(stream);
  }).catch(function(err) {
      console.log("Unable to get video stream: " + err);
  });
}

function snapshot(){
  myCanvas.getContext('2d').drawImage(myVideo, 0, 0, videoWidth, videoHeight);
}

<!DOCTYPE html>
<html>
<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="debug.js"></script>
</head>
<body onload="init()">
    <div id="mainContainer">
        <video id="myVideo" width="640" height="480" autoplay style="display: inline;"></video>
        <canvas id="myCanvas" width="640" height="480" style="display: inline;"></canvas>
        <input type="button" id="snapshotButton" value="Snapshot" onclick="snapshot()"/>
    </div>
</body>
</html>

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The fact is that I do not want to use the button for a snapshot, but I will take a picture as soon as the camera stream loads. I tried to call the snapshot function () immediately after setting the video source:

function init(){
  myVideo = document.getElementById("myVideo") 
  myCanvas = document.getElementById("myCanvas");
  videoWidth = myCanvas.width;
  videoHeight = myCanvas.height;
    
  startVideoStream();
}

function startVideoStream(){
  navigator.mediaDevices.getUserMedia({audio: false, video: { width: videoWidth, height: videoHeight }}).then(function(stream) {
    myVideo.src = URL.createObjectURL(stream);
    snapshot();
  }).catch(function(err) {
      console.log("Unable to get video stream: " + err);
  });
}

function snapshot(){
  myCanvas.getContext('2d').drawImage(myVideo, 0, 0, videoWidth, videoHeight);
}

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But that will not work. My canvas remains white. I assume that at this point the camera stream is not fully loaded.

So, are there any other events that can be used to draw a snapshot as soon as the camera’s power is loaded? Or am I completely mistaken?

Thanks in advance!

+5

javascript getusermedia

xcess Jan 25 '17 at 15:28

1

jib · Accepted Answer · 2017-01-26T04:31:29+0000

loadedmetadata:

navigator.mediaDevices.getUserMedia({video: true})
  .then(stream => {
    video.srcObject = stream;
    return new Promise(resolve => video.onloadedmetadata = resolve);
  })
  .then(() => canvas.getContext('2d').drawImage(video, 0, 0, 160, 120))
  .catch(e => console.log(e));

<video id="video" width="160" height="120" autoplay></video>
<canvas id="canvas" width="160" height="120"></canvas>

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( WebRTC).

Chrome , play() .

, URL.createObjectURL(stream) . srcObject.

: @KyleMcDonald , loadedmetadata srcObject ! — .

Callback event for getUserMedia ()

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