<input type="file"/>
document.querySelector('input[type="file"]').addEventListener('change',function () {
    document.querySelector('video').src = window.URL.createObjectURL(this.files[0])
})

var canvas = document.createElement("canvas");
var canvasCtx = canvas.getContext("2d");
var video=document.querySelector('video');
//坐原图像的x,y轴坐标，大小，目标图像的x，y轴标，大小。
canvasCtx.drawImage(video, 0, 0, videoWidth, videoHeight, 0, 0, imgWidth, imgHeight);
//把图标base64编码后变成一段url字符串
var dataUrl = canvas.toDataURL("image/png");
//插入图片得src特性中
document.createElement('img').src=dataUrl;

function getOffset(elem) {
    var pos = {x: elem.offsetLeft, y: elem.offsetTop};
    var offsetParent = elem.offsetParent;
    while (offsetParent) {
        pos.x += offsetParent.offsetLeft;
        pos.y += offsetParent.offsetTop;
        offsetParent = offsetParent.offsetParent;
    }
    return pos;
}

var $imgBig = $("<img/>");
//设置大图片的初始位置，就是原视频处。
$imgBig.css({
    position: "absolute",
    left: video.offsetLeft,
    top: video.offsetTop,
    width: video.offsetWidth+ "px",
    height: video.offsetHeight+ "px"
}).attr("src", dataUrl);
var $img = $("<img/>");
$img.hide();
//获取小图片的距离参数，实现大图片的动画效果。
var offset = getOffset($img[0]);
//添加动画效果
$imgBig.animate({
    left: offset.x + "px",
    top: offset.y + "px",
    width: $img.width() + "px",
    height: $img.height() + "px"
}, 500, function () {
    $img.show();
    $imgBig.remove();
});