writing and reading high definition frames to a file

edit

I am using frames described by:

cap.set(CV_CAP_PROP_FOURCC, CV_FOURCC('H', '2', '6', '4'));
cap.set(CV_CAP_PROP_FOURCC, CV_FOURCC('M', 'J', 'P', 'G'));
cap.set(CV_CAP_PROP_FRAME_WIDTH, 1920);
cap.set(CV_CAP_PROP_FRAME_HEIGHT, 1080);
cap.set(CV_CAP_PROP_FPS, 30);

Issue is writing the frame to a file and then reading it back in the original HD format. imwriting to file as a .jpeg and imreading it back to the same frame.