Assignment between unlike types is not allowed. Upsampling

I am trying to up and downsample a video as an assignment. i can downsample it without a problem but while upsampling it all i get is this error. Alternatively i tried to use interp and resample functions but then i get "the arguments should be double"... Am i doing something wrong here?

clc;
clear all;
I=aviread('Car_video.avi');
obj=mmreader('Car_video.avi');
a=read(obj);
frames=get(obj,'numberofFrames');
for k=1: frames-1
  I(k).cdata=a(:,:,:,k);
  I(k).colormap =[];
end
%movie2avi(I,'car original.avi','compression','none','fps',30);
%d1=downsample(I,2);
%movie2avi(d1,'car downsample at 2.avi','compression','none','fps',30);
%d2=downsample(I,5);
%movie2avi(d2,'car downsample at 5.avi','compression','none','fps',30);
u=upsample(I,2);
movie2avi(u,'car upsample at 2.avi','compression','none','fps',30);

??? Assignment between unlike types is not allowed.
Error in ==> updownsample at 30
  y(1:m*N*n) = 0; % Don't use zeros() because it doesn't support fi objects

Error in ==> upsample at 15
y = updownsample(x,N,'Up',varargin{:});

Answer 1

[Walter Roberson]

You cannot pass frames to upsample() or downsample() : you have to pass signals.

It appears to me that upsample() and downsample() work along the first dimension of the data. It is not clear to me which dimension you want to resample along -- possibly the time dimension. If so then

u_a = permute( upsample( permute(a, [4 1 2 3]), 2 ), [2 3 4 1]);

and then break u_a down into frames.