Function isBlankFrame

src/__tests__/MediaStreamRecorder.js:1917–1968

(frame, _pixTolerance, _frameTolerance)

    var self = this;

    function isBlankFrame(frame, _pixTolerance, _frameTolerance) {
        var localCanvas = document.createElement('canvas');
        localCanvas.width = canvas.width;
        localCanvas.height = canvas.height;
        var context2d = localCanvas.getContext('2d');

        var sampleColor = {
            r: 0,
            g: 0,
            b: 0
        };
        var maxColorDifference = Math.sqrt(
            Math.pow(255, 2) +
            Math.pow(255, 2) +
            Math.pow(255, 2)
        );
        var pixTolerance = _pixTolerance && _pixTolerance >= 0 && _pixTolerance <= 1 ? _pixTolerance : 0;
        var frameTolerance = _frameTolerance && _frameTolerance >= 0 && _frameTolerance <= 1 ? _frameTolerance : 0;

        var matchPixCount, endPixCheck, maxPixCount;

        var image = new Image();
        image.src = frame.image;
        context2d.drawImage(image, 0, 0, canvas.width, canvas.height);
        var imageData = context2d.getImageData(0, 0, canvas.width, canvas.height);
        matchPixCount = 0;
        endPixCheck = imageData.data.length;
        maxPixCount = imageData.data.length / 4;

        for (var pix = 0; pix < endPixCheck; pix += 4) {
            var currentColor = {
                r: imageData.data[pix],
                g: imageData.data[pix + 1],
                b: imageData.data[pix + 2]
            };
            var colorDifference = Math.sqrt(
                Math.pow(currentColor.r - sampleColor.r, 2) +
                Math.pow(currentColor.g - sampleColor.g, 2) +
                Math.pow(currentColor.b - sampleColor.b, 2)
            );
            // difference in color it is difference in color vectors (r1,g1,b1) <=> (r2,g2,b2)
            if (colorDifference <= maxColorDifference * pixTolerance) {
                matchPixCount++;
            }
        }

        if (maxPixCount - matchPixCount <= maxPixCount * frameTolerance) {
            return false;
        } else {
            return true;
        }
    }

    function dropBlackFrames(_frames, _framesToCheck, _pixTolerance, _frameTolerance) {
        var localCanvas = document.createElement('canvas');