Wednesday, 13 February 2013

Camera and Video Control with HTML5

Client-side APIs on mobile and desktop devices are quickly providing the same APIs.  Of course our mobile devices got access to some of these APIs first, but those APIs are slowly making their way to the desktop.  One of those APIs is the getUserMedia API, providing developers access to the user's camera.  Let me show you how to get simple camera access from within your browser!



Please read my note about the HTML structure below:
  Ideally these elements aren't created until it's confirmed that the 
  client supports video/camera, but for the sake of illustrating the 
  elements involved, they are created with markup (not JavaScript)
<video id="video" width="640" height="480" autoplay></video>
<button id="snap">Snap Photo</button>
<canvas id="canvas" width="640" height="480"></canvas>

Each of these elements should be created once confirmation of camera support is confirmed, but for the sake of this tutorial, I wanted to show you what the elements look like with basic HTML.  Do note that the dimensions we're working with are 640x480.

The JavaScript

Since the HTML elements above are already created, the JavaScript portion will look smaller than you think:
// Put event listeners into place
window.addEventListener("DOMContentLoaded", function() {
  // Grab elements, create settings, etc.
  var canvas = document.getElementById("canvas"),
    context = canvas.getContext("2d"),
    video = document.getElementById("video"),
    videoObj = { "video": true },
    errBack = function(error) {
      console.log("Video capture error: ", error.code); 

  // Put video listeners into place
  if(navigator.getUserMedia) { // Standard
    navigator.getUserMedia(videoObj, function(stream) {
      video.src = stream;;
    }, errBack);
  } else if(navigator.webkitGetUserMedia) { // WebKit-prefixed
    navigator.webkitGetUserMedia(videoObj, function(stream){
      video.src = window.webkitURL.createObjectURL(stream);;
    }, errBack);
}, false);
Once it's been established that the browser supports getUserMedia, a simple method sets the video element's src to the user's live camera/webcam.  Calling the play method of the video then enacts the element's live video connection.  That's all that's required to connect your camera to the browser!
Taking a photo is only marginally more difficult.  Simply add a click listener to a generic button and and draw an image from video!
// Trigger photo take
document.getElementById("snap").addEventListener("click", function() {
  context.drawImage(video, 0, 0, 640, 480);
Of course you could add some sexy image filters and make a billion dollars...but I'll save that for another post.  At minimum you could convert the canvas snapshot to an image though!  I'll talk about canvas image filters in the future...

Being able to access the camera within the browser without using third party software is an incredible advancement.  Paired with canvas and a bit of JavaScript, the camera has become quickly and easily accessible.  Not only it the camera accessible, but since canvas is ultra-flexible, we'll be able to add sexy Instagram-style image filters in the future.  For now, however, simply accessing the camera in our browser moves us miles ahead.  Have fun taking images within your browser!
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  1. In fact you may be punished by the insurance company if you don't install video monitoring video camera. Cameras can be used to observe worker conformity with rules and help to spot safety risks or methods.