Display web camera on canvas element

#javascript #webdev #programming #beginners

Lets view the video stream from web camera on canvas so we can benefit from canvas capabilities (text on video ,add filters and more).

Basic html

	<!doctype html>
	<html lang="en">
	<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<!-- Bootstrap CSS -->
	<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3" crossorigin="anonymous">

	<title>Video on canvas</title>
	</head>
	<body>

	<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/js/bootstrap.bundle.min.js" integrity="sha384-ka7Sk0Gln4gmtz2MlQnikT1wXgYsOg+OMhuP+IlRH9sENBO0LRn5q+8nbTov4+1p" crossorigin="anonymous"></script>
	</body>
	</html>

view raw index_1.html hosted with ❤ by GitHub

Create a javascript file index.js and add a reference to the html at line 15:

<script src="index.js"></script>

Next we will create a video element which will be hidden because we want to view the canvas element:

<video autoplay playsinline webkit-playsinline muted hidden id="videoelement"></video>

Now lets add a canvas element inside a bootstrap container:

    <div class="container">
        <canvas id="canvaselement" width="1920" height="1080"></canvas>
    </div>

The final html:

	<!doctype html>
	<html lang="en">
	<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<!-- Bootstrap CSS -->
	<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3" crossorigin="anonymous">

	<title>Video on canvas</title>
	</head>
	<body>
	<video autoplay playsinline webkit-playsinline muted hidden id="videoelement"></video>
	<div class="container">
	<canvas id="canvaselement" width="1920" height="1080"></canvas>
	</div>


	<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.1.3/dist/js/bootstrap.bundle.min.js" integrity="sha384-ka7Sk0Gln4gmtz2MlQnikT1wXgYsOg+OMhuP+IlRH9sENBO0LRn5q+8nbTov4+1p" crossorigin="anonymous"></script>
	</body>
	</html>

view raw index.html hosted with ❤ by GitHub

Now that we have a bootstrap html template lets add javascript:

	var videoelement = document.getElementById("videoelement");
	var localStreamConstraints = {
	audio: true,
	video: { width: 1920, height: 1080 },
	};

	if (videoelement) {
	navigator.mediaDevices
	.getUserMedia(localStreamConstraints)
	.then(gotStream)
	.catch(function (e) {
	if (confirm("An error with camera occured:(" + e.name + ") Do you want to reload?")) {
	location.reload();
	}
	});
	}
	//if found stream found
	function gotStream(stream) {
	videoelement.srcObject = stream
	}

view raw index_1.js hosted with ❤ by GitHub

Code explanation

At line 9 we prompt the user for permission to use camera and microphone
If the user accepts then at line 10 the gotStream function is executed.
gotStream add as source of video the stream of camera and microphone
If the user denies the permission or stream is inaccessible then at line 11 we prompt the user to reload the page in order to try again

Now that we added the video element and we set the stream of camera to the video element lets add a canvas that will display frames of video:

	var videoelement = document.getElementById("videoelement");
	var streamContraints = {
	audio: true,
	video: { width: 1920, height: 1080 },
	};
	var canvaselement = document.querySelector('#canvaselement');
	var ctx = canvaselement.getContext('2d', { alpha: false });
	var canvasInterval = null;
	var fps=60


	if (videoelement) {
	navigator.mediaDevices
	.getUserMedia(streamContraints)
	.then(gotStream)
	.catch(function (e) {
	if (confirm("An error with camera occured:(" + e.name + ") Do you want to reload?")) {
	location.reload();
	}
	});
	}
	//if stream found
	function gotStream(stream) {
	videoelement.srcObject = stream
	videoelement.play()
	}


	function drawImage(video) {
	ctx.drawImage(video, 0, 0, canvaselement.width, canvaselement.height);
	}
	canvasInterval = window.setInterval(() => {
	drawImage(videoelement);
	}, 1000 / fps);