Is Video Dark?

isVideoDark.js

function isVideoDark(videoEl) {
    var fuzzy = 0.1;
    // create canvas
    var canvas = document.createElement("canvas");
    var videoWidth = videoEl.videoWidth;
    var videoHeight =  videoEl.videoHeight;
    canvas.width = videoWidth;
    canvas.height = videoHeight;

    var ctx = canvas.getContext("2d");
    ctx.drawImage(videoEl, 0, 0);

    var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
    var data = imageData.data;
    var r, g, b, max_rgb;
    var light = 0, dark = 0;

    for(var x = 0, len = data.length; x < len; x+=4) {
        r = data[x];
        g = data[x+1];
        b = data[x+2];

        max_rgb = Math.max(Math.max(r, g), b);
        if (max_rgb < 128)
            dark++;
        else
            light++;
    }

    var dl_diff = ((light - dark) / (videoWidth * videoHeight));
    if (dl_diff + fuzzy < 0)
        return true; /* Dark. */
    else
        return false;  /* Not dark. */
}

This is a modified version of the script @ http://jsfiddle.net/s7Wx2/328/