can exist 2 channel within one vedio frame?why we count frames in algorithm part on matlab

function grmovstruct = myvideo(structname)

fcount = size(structname,2); for i = fcount:-1:1

    grvedio = rgb2gray(structname(i).cdata);
    imshow(grvedio);
    grmovstruct(i) = getframe;
end
movie(grmovstruct);
end