normalize output file name

src/optflow/optflow-demo.cpp

@@ -190,7 +190,7 @@ int main(int argc, char **argv) {
     }
 
     double fps = capture.get(cv::CAP_PROP_FPS);
-    cv::VideoWriter writer("optflow.mkv", cv::CAP_FFMPEG, cv::VideoWriter::fourcc('V', 'P', '9', '0'), fps, cv::Size(WIDTH, HEIGHT), {
+    cv::VideoWriter writer("optflow-demo.mkv", cv::CAP_FFMPEG, cv::VideoWriter::fourcc('V', 'P', '9', '0'), fps, cv::Size(WIDTH, HEIGHT), {
             cv::VIDEOWRITER_PROP_HW_ACCELERATION, cv::VIDEO_ACCELERATION_VAAPI,
             cv::VIDEOWRITER_PROP_HW_ACCELERATION_USE_OPENCL, 1
     });