How to write dlib shape_pedictor together with the video capture - c++

Question

I am trying to write each frame from a camera into a video. Till here it is fine. However, I want my video to include the shape_predictor too at each frame, so when it is reproduced it also appears on the image. So far I have got this... Any ideas? Thank you
cap >> frame;
cv::VideoWriter oVideoWriter;
// . . .
cv_image<bgr_pixel> cimg(frame); //Mat to something dlib can deal with
frontal_face_detector detector = get_frontal_face_detector();
std::vector<rectangle> faces = detector(cimg);
pose_model(cimg, faces[0]);
oVideoWriter.write(dlib::toMat(cimg)); //Turn it into an Opencv Mat

Answer 1

The shape predictor is not the face detector. You have to first call the face detector, then the shape predictor.
See this example program: http://dlib.net/face_landmark_detection_ex.cpp.html
You initialized the face detector properly..then you have to initialize the tracker. Something like this:
shape_predictor sp;
deserialize("shape_predictor_68_face_landmarks.dat") >> sp;
The model can be found here: http://sourceforge.net/projects/dclib/files/dlib/v18.10/shape_predictor_68_face_landmarks.dat.bz2
The rest of the way, you can just follow the example program I linked above. Here's the portion where the tracker is run. You have to pass to the tracker the output (bounding box) return by the detector for it to work. The code below iterates through all the boxes returned by the detector.
// Now tell the face detector to give us a list of bounding boxes
// around all the faces in the image.
std::vector<rectangle> dets = detector(img);
cout << "Number of faces detected: " << dets.size() << endl;
// Now we will go ask the shape_predictor to tell us the pose of
// each face we detected.
std::vector<full_object_detection> shapes;
for (unsigned long j = 0; j < dets.size(); ++j)
{
full_object_detection shape = sp(img, dets[j]);
cout << "number of parts: "<< shape.num_parts() << endl;
cout << "pixel position of first part: " << shape.part(0) << endl;
cout << "pixel position of second part: " << shape.part(1) << endl;
// You get the idea, you can get all the face part locations if
// you want them. Here we just store them in shapes so we can
// put them on the screen.
shapes.push_back(shape);
}