Chrome中的HTML5视频在mp4下不起作用

我正在一个简单的网站上工作，在画布上显示视频。 视频显示，但它只是卡在第一帧，我设置了控件并且自动播放既不显示也不播放视频。

<div style="position: absolute; top: 50px; left: 50px;">
<canvas id="canvasOne" width="500" height="300">
Your browser does not support HTML5 Canvas.
</canvas>
</div>
@section Scripts
{
<script src="@Url.Content("~/Scripts/modernizr-2.5.3.js")" type="text/javascript">        </script>
<script type="text/javascript">
    window.addEventListener('load', eventWindowLoaded, false);
    var firstVideo, secondVideo, videoSource
    var videoDiv;
    function eventWindowLoaded() {
        firstVideo = document.createElement("video");
        videoSource = document.createElement("source");
        firstVideo.appendChild(videoSource);
        //secondVideo = document.createElement("video");
        videoDiv = document.createElement('div');
        document.body.appendChild(videoDiv);
        videoDiv.appendChild(firstVideo);
       //videoDiv.appendChild(secondVideo);
        videoDiv.setAttribute("style", "display:none;");
        var videoType = supportedVideoFormat(firstVideo);       
        if (videoType == "") {
            alert("no video support");
            return;
        }
        videoSource.setAttribute("src", "/Content/QualitySample." + videoType);
        videoSource.setAttribute("type", "video/mp4");
        firstVideo.setAttribute("controls", "controls");
        firstVideo.setAttribute("autoplay", "autoplay");
        firstVideo.addEventListener("canplaythrough", videoLoaded, false);
        //secondVideo.setAttribute("src", "/Content/QualitySample." + videoType);
        //secondVideo.setAttribute("controls", "controls");
        //secondVideo.addEventListener("canplaythrough", videoLoaded, false);

    }
    function supportedVideoFormat(video) {
        var returnExtension = "";
        if (video.canPlayType("video/mp4") == "probably" ||
       video.canPlayType("video/mp4") == "maybe") {
            returnExtension = "mp4";
    } else if (video.canPlayType("video/webm") == "probably" ||
   video.canPlayType("video/webm") == "maybe") {
        returnExtension = "webm";
    } else if (video.canPlayType("video/ogg") == "probably" ||
   video.canPlayType("video/ogg") == "maybe") {
        returnExtension = "ogg";
    }

    return returnExtension;
}
function canvasSupport() {
    return Modernizr.canvas;
}
function videoLoaded(event) {
    canvasApp();
}
function canvasApp() {
    if (!canvasSupport()) {
        return;
    }
    function drawScreen() {
        //Background
        context.fillStyle = '#ffffff';
        context.fillRect(0, 0, theCanvas.width, theCanvas.height);
        //Box
        context.strokeStyle = '#000000';
        context.strokeRect(5, 5, theCanvas.width - 10, theCanvas.height - 10);
        //video
        context.drawImage(firstVideo, 60, 50, 200, 200);
        //context.drawImage(secondVideo, 260, 50, 200, 200);
    }
    var theCanvas = document.getElementById("canvasOne");
    var context = theCanvas.getContext("2d");
    //firstVideo.load();
    firstVideo.play();
    //secondVideo.play();
    setInterval(drawScreen, 33);
}

}当页面加载时，视频将显示在画布上并加载视频，但没有控件处于活动状态，也不会播放。