Method getBestThumbnailIndex

libffmpegthumbnailer/videothumbnailer.cpp:331–374

}

int VideoThumbnailer::getBestThumbnailIndex(vector<VideoFrame>& videoFrames, const vector<Histogram<int>>& histograms)
{
    Histogram<float> avgHistogram;
    for (auto&& histogram : histograms) {
        for (int j = 0; j < 255; ++j) {
            avgHistogram.r[j] += static_cast<float>(histogram.r[j]) / histograms.size();
            avgHistogram.g[j] += static_cast<float>(histogram.g[j]) / histograms.size();
            avgHistogram.b[j] += static_cast<float>(histogram.b[j]) / histograms.size();
        }
    }

    int bestFrame = -1;
    float minRMSE = FLT_MAX;
    for (size_t i = 0; i < histograms.size(); ++i) {
        // calculate root mean squared error
        float rmse = 0.0;
        for (int j = 0; j < 255; ++j) {
            float error = fabsf(avgHistogram.r[j] - histograms[i].r[j]) + fabsf(avgHistogram.g[j] - histograms[i].g[j]) + fabsf(avgHistogram.b[j] - histograms[i].b[j]);
            rmse += (error * error) / 255;
        }

        rmse = sqrtf(rmse);
        if (rmse < minRMSE) {
            minRMSE   = rmse;
            bestFrame = i;
        }

#ifdef DEBUG_MODE
        stringstream outputFile;
        outputFile << "frames/Frame" << setfill('0') << setw(3) << i << "_" << rmse << endl;
        std::unique_ptr<ImageWriter> imageWriter(ImageWriterFactory<const string&>::createImageWriter(Png, outputFile.str()));
        vector<uint8_t*> rowPointers;
        for (int x = 0; x < videoFrames[i].height; ++x)
            rowPointers.push_back(&(videoFrames[i].frameData[x * videoFrames[i].lineSize]));
        imageWriter->writeFrame(&(rowPointers.front()), videoFrames[i].width, videoFrames[i].height, m_ImageQuality);
#endif
    }

#ifdef DEBUG_MODE
    cout << "Best frame was: " << bestFrame << "(RMSE: " << minRMSE << ")" << endl;
#endif

    return bestFrame;
}

void VideoThumbnailer::TraceMessage(ThumbnailerLogLevel lvl, const std::string& msg)
{