Get the size of each compressed mj2 frame

I used the VideoReader Class to read a Motion JPEG2000 mj2 file and was able to play it using the example in the documentation. But what I need is the size of each compressed frame in bytes. The object created from VideoReader is decompressed.

obj = VideoReader('j2kvid.mj2');
vidWidth = cr10Obj.Width;
vidHeight = cr10Obj.Height;

mov = struct('cdata',zeros(vidWidth,vidHeight,3,'uint8'),'colormap',[]);

k = 1;
while hasFrame(obj)
    mov(k).cdata = readFrame(obj);
    k = k+1;
end

I just want an array with each element being the size of each compressed frame. Anyone one have an idea how I can do this?

Mike