Given FrameRate does not match with real FrameRate

I am testing my laptop integrated cam, and after writing this simple code, FrameRates doesn't match. It shows that it's 30fps, but after calc I can see it's the half, 15fps. This is the code:

    vid = videoinput('winvideo',1);
    frameRates = set(getselectedsource(vid), 'FrameRate')
    vid.FramesPerTrigger = 30;
    start(vid); [frames, timeStamp] = getdata(vid);
    frameRateCalc = 1/mean(diff(timeStamp))

And this is the output

    >> framerate

    frameRates = 

        '30.0000'

    frameRateCalc =

       15.2007

I have tested with another external cam and seems to work fine, 30 match with 30. Anybody knows why they doesn't match with the integrated cam?

Answer 1

[hong chan]

with your code,my GUI can draw it correctly.