如何将html5视频捕获上传到服务器?

我得到了如下html5视频捕获:

        var canvas = document.createElement('canvas');
        canvas.height = video.height;
        canvas.width = video.width;
        var ctx = canvas.getContext('2d');
        ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
        capturedImage=ctx.getImageData(0,0,canvas.width,canvas.height))

并尝试像这样上传此捕获:

$.ajax({
         type: method,
         contentType: false,
         cache: false,
         processData: false,
         async: false,
         url: '....',
         data: capturedImage,<----------how to convert above captured image here?
   }).done(function(o) {
        .....
   });

如果只是:

data:capturedImage

后端将获得如下数据值:

str:imageObject

ajax请求只是将一个str发送到后端,那么如何转换此捕获的图像以让ajax上传工作?