我试图从视频中捕获一个帧并使用HTML5将其绘制到画布,但下面的代码无法正常工作。当我使用.mp4
格式的视频源并单击开始按钮时,画布将填充黑色。
但我可以获得'.ogv'格式视频源的正确捕捉图像。这是用于捕获帧的代码:
<script type="text/javascript">
var videoId = 'video';
var scaleFactor = 0.25;
var snapshots = [];
/**
* Captures a image frame from the provided video element.
*
* @param {Video} video HTML5 video element from where the image frame will be captured.
* @param {Number} scaleFactor Factor to scale the canvas element that will be return. This is an optional parameter.
*
* @return {Canvas}
*/
function capture(video, scaleFactor) {
if(scaleFactor == null){
scaleFactor = 1;
}
var w = video.videoWidth * scaleFactor;
var h = video.videoHeight * scaleFactor;
var canvas = document.createElement('canvas');
canvas.width = w;
canvas.height = h;
var ctx = canvas.getContext('2d');
ctx.drawImage(video, 0, 0, w, h);
return canvas;
}
/**
* Invokes the <code>capture</code> function and attaches the canvas element to the DOM.
*/
function shoot(){
var video = document.getElementById(videoId);
var output = document.getElementById('output');
var canvas = capture(video, scaleFactor);
canvas.onclick = function(){
window.open(this.toDataURL());
};
snapshots.unshift(canvas);
output.innerHTML = '';
for(var i=0; i<4; i++){
output.appendChild(snapshots[i]);
}
}
</script>