javascript - JS直接从视频流中获取图片作为数据url

Question

我如何直接从视频捕获转到 javascript 中的数据 url？我想将图像作为调整后的版本显示给用户，但保留完整尺寸的图像。那么，我该怎么做呢？

var PhotoBooth = {
    onMediaStream: function(stream) {
        PhotoBooth.canvas = $('canvas')[0];
        PhotoBooth.context = PhotoBooth.canvas.getContext('2d');

        PhotoBooth.localVideo = $('video')[0];
        PhotoBooth.localVideo.src = window.URL.createObjectURL(stream);
    },
    noStream: function() {
        console.log('FAIL TO GET WEBCAM ACCESS');
    }
};

getUserMedia(
    {video: true},
    PhotoBooth.onMediaStream,
    PhotoBooth.noStream
);

这就是我目前保存图片以供上传的方式:

PhotoBooth.context.drawImage(PhotoBooth.localVideo, 0, 0, 200, 150);
$('#preview').show();

然后我像这样检索保存的图像:

var dataUrl = PhotoBooth.canvas.toDataURL();

我想让 Canvas 保持默认大小，但保留实际数据。基本上，我希望 Canvas 显示调整大小的版本，但保持完整大小的版本。

Answer 1

此处，canvas 保留了原始的 640x480 快照(Chrome 使用 https fiddle):

var start = () => navigator.mediaDevices.getUserMedia({ video: true })
  .then(stream => video.srcObject = stream)
  .catch(log);

var canvas = document.createElement("canvas");
canvas.width = 640;
canvas.height = 480;

var snap = () => {
  canvas.getContext('2d').drawImage(video, 0, 0, 640, 480);
  preview.getContext('2d').drawImage(canvas, 0, 0, 160, 120);
}

var log = msg => div.innerHTML += "<br>" + msg;

<button onclick="start()">Start!</button>
<button onclick="snap()">Snap!</button><div id="div"></div>
<video id="video" width="160" height="120" autoplay></video>
<canvas id="preview" width="160" height="120"></canvas>