How to apply this process on a FITS file?

Hi there, I need to apply the process in the following script on a FITS file instead of the inserted function/signal "splat" :

load splat

sg = 400;
ov = 300;

spectrogram(y,sg,ov,[],Fs,'yaxis')

    colormap bone
  [s,f,t,p] = spectrogram(y,sg,ov,[],Fs);
  f1 = f > 100;
  t1 = t < 0.75;

m1 = medfreq(p(f1,t1),f(f1));
f2 = f > 2500;
t2 = t > 0.3 & t < 0.65;

m2 = medfreq(p(f2,t2),f(f2));
hold on
plot(t(t1),m1/1000,'linewidth',4)
plot(t(t2),m2/1000,'linewidth',4)
hold off

I supposed to get output like that:

But even this output I couldn't get, because there's no median frequency function installed with MATLAB. Would you please send m-file for medfreq and tell me how to write a script do what I want here?