I can't move TrackBar - c++

Question

I am coding opencv source for playing video. I want to add trackBar and adjust video speed. But, The TrackBar does't move. and I can't focus the Video window. This is my code OpenCv C++. What should i do?
void onTrackbarSlide(int pos, void *){
sec = 1;
sec /= pos;
printf("pos = %d\n",pos);
}
int main(void)
{
strcat(InputFile, FileName); // input video file
//VideoCapture cap(0); // Create an object and open the default(0) camera. C++ Syntax: VideoCapture::VideoCapture(int device)
VideoCapture cap; // Class for video capturing from video files or cameras.
cap.open(InputFile); // Open video file or a capturing device for video capturing
if (!cap.isOpened()) { // Check if the file is opened sucessfully.
printf("\nFail to open a video file");
return -1;
}
// When querying a property that is not supported by the backend used by the VideoCapture class, value 0 is returned.
double fps = cap.get(CV_CAP_PROP_FPS); printf("\nCV_CAP_PROP_FPS = %f", fps);
double ToTalFrames = cap.get(CV_CAP_PROP_FRAME_COUNT); printf("\nCV_CAP_PROP_FRAME_COUNT = %f", fps);
CvSize FrameSize;
FrameSize.width = (int)cap.get(CV_CAP_PROP_FRAME_WIDTH);
FrameSize.height = (int)cap.get(CV_CAP_PROP_FRAME_HEIGHT);
printf("\nWidth * Height = %d * %d\n", FrameSize.width, FrameSize.height);
VideoWriter wrt;
#define CODEC -1
namedWindow("original", 1);
int slider_position = 0;
int slider_max = 255;
createTrackbar("video speed", "original", &slider_position, slider_max, onTrackbarSlide);
wrt.open(OutputFile, CODEC, fps, FrameSize);
Mat frame, dst1;
Mat dst2;
for (int i = 1; i< ToTalFrames; i++)
{
cap.read(frame);
if (frame.data == NULL) { printf("\nNo image found!\n"); return(0); }
imshow("original", frame);
if( waitKey(sec /fps) == 0x1b ) break; // Break if key input is escape code.
}
return 0;
}