Function dropBlackFrames

src/__tests__/MediaStreamRecorder.js:1970–2044

(_frames, _framesToCheck, _pixTolerance, _frameTolerance)

    }

    function dropBlackFrames(_frames, _framesToCheck, _pixTolerance, _frameTolerance) {
        var localCanvas = document.createElement('canvas');
        localCanvas.width = canvas.width;
        localCanvas.height = canvas.height;
        var context2d = localCanvas.getContext('2d');
        var resultFrames = [];

        var checkUntilNotBlack = _framesToCheck === -1;
        var endCheckFrame = (_framesToCheck && _framesToCheck > 0 && _framesToCheck <= _frames.length) ?
            _framesToCheck : _frames.length;
        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 doNotCheckNext = false;

        for (var f = 0; f < endCheckFrame; f++) {
            var matchPixCount, endPixCheck, maxPixCount;

            if (!doNotCheckNext) {
                var image = new Image();
                image.src = _frames[f].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 (!doNotCheckNext && maxPixCount - matchPixCount <= maxPixCount * frameTolerance) {
                // console.log('removed black frame : ' + f + ' ; frame duration ' + _frames[f].duration);
            } else {
                // console.log('frame is passed : ' + f);