I'm attempting to use a the first frame of a video as the background of a canvas, as you probably guessed from the title of the question. I can set a background, I can get a frame from a video, but I can't make the frame be the background. It looks like I need a url for the frame to set as the background in the CSS style. For that, I need a blob on which I can call createObjURL() (although I'm discovering now that that method may be deprecated/ing).
Here's some code:
<!DOCTYPE html>
<html lang="en">
<canvas id="back" style="background-image: url('path/to/.png')";></canvas>
<input type="file" accept="video/*" />
<script>
document.querySelector('input').addEventListener('change', extractFrame, false);
var canvas = document.getElementById('back');
var context = canvas.getContext('2d');
var imageObj = new Image();
var image;
imageObj.onload = function() {
var height = imageObj.height;
var width = imageObj.width;
canvas.height = height;
canvas.width = width;
context.drawImage(imageObj, 0, 0, back.width, back.height);
};
imageObj.src = "path/to/.png";
var draw_canvas = document.getElementById('back');
var draw_context = draw_canvas.getContext('2d');
var corners = [];
draw_canvas.addEventListener('mousedown',startDrawing,false);
function startDrawing(e){
corners.length=0;
corners.push([e.layerX, e.layerY]);
corners.push([e.layerX+1, e.layerY+1]);
draw_canvas.addEventListener('mousemove', updateCorners,false);
draw_canvas.addEventListener('mouseup',function(){
draw_canvas.removeEventListener('mousemove', updateCorners,false);
},false);
}
function updateCorners(e){
corners[1] = [e.layerX, e.layerY]
redraw();
}
function redraw(){
draw_context.clearRect(0, 0, canvas.width, canvas.height);
draw_context.beginPath()
draw_context.lineWidth = "2";
draw_context.strokeStyle = "red";
draw_context.rect(corners[0][0], corners[0][1], corners[1][0] - corners[0][0], corners[1][1] - corners[0][1]);
draw_context.stroke();
}
function extractFrame(){
var video = document.createElement('video');
var array = [];
function initCanvas(){
canvas.width = this.videoWidth;
canvas.height = this.videoHeight;
}
function drawFrame(e) {
this.pause();
context.drawImage(this, 0, 0);
var blob = canvas.toBlob(saveFrame, 'image/png');
var dataUrl = URL.createObjectURL(array[0]);
document.getElementById('back').style.background = "url('${dataUrl}')";
URL.revokeObjectURL(dataUrl);
}
function saveFrame(blob) {
console.log(array);
array.push(blob);
console.log(array);
}
video.muted = true;
video.addEventListener('loadedmetadata', initCanvas, false);
video.addEventListener('timeupdate', drawFrame, false);
video.src = URL.createObjectURL(this.files[0]);
video.play();
}
</script>
I've been messing with the ordering of the code, the objects I'm passing, etc. all day now and I have no idea what's keeping this from working. If it helps, one of the errors I get most often is
Failed to execute 'createObjectURL' on 'URL': Overload resolution failed.
Which a different question said may be because the object in the array is undefined or None or however JS describes it, but the logged array says that it is populated with blobs.
Any suggestions are appreciated. Happy to provide more code or specs if I can. Thanks!
EDIT: I've added more code so that it can be reproduced (I hope). I'm not hosting it anywhere but locally, so I hope this works for y'all.
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