Help get this code working please

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MatLab

Hi everyone
I've got this project on MATLAB where i'm trying to read in a YUV file.

Below are the m files within my work directory

function [width,height,fps,startpos,NumberFrames]=readheader(fid)

%********************************************************
% This function will read the header of a bath yuv file
%
% This file is used by readyseq and should not be used on its own.
%
% N.Young
% 5 June 2001
%********************************************************

FileFormat = [];
%The first line will contain one of the following

%1.   YUV 4:2:0
%2.   RVS RAW YUV 4:2:0

%read the format descriptor
for i=1:17
  FileFormat = [FileFormat fscanf(fid,'%c',1)];

  %Check to see if it is yuv 420 (i.e. number 1 above)
  if i==9
    if FileFormat == 'YUV 4:2:0'
      disp('File format is : YUV 4:2:0');
      FileFormat=0;
      break;
    end
  end

  %Check to see if it is rvs raw yuv 420 (i.e. number 2 above)
  if i==17
    if FileFormat == 'RVS RAW YUV 4:2:0'
      disp('File format is : RVS RAW YUV 4:2:0');
      FileFormat=1;
      break;
    end
  end

  %if we get here and i is 17, we have an unsupported FileFormat
  if i==17
    disp('Unknown file format')
    FileFormat = 2;
  end
end

if FileFormat==0
  [width,height,fps,startpos,NumberFrames] = readyuvheader(fid);
end

function [width,height,y]=readyseq(filename,start,stop)
%********************************************************
% Function to load a bath yuv file
%
% Syntax : [width,height,ysequence] = readyseq(filename,start frame,end frame)
%
% NOTE: the frames are numbered from 0.
%
% A.N.Evans & N.Young
% 5 June 2001
%********************************************************

%Note that I have to use some C functions here.  I know some people dont like
%mixing matlab with c, I'm affraid its un avoidable.

%First we need to open the file
[fid,msg] = fopen(filename,'r');

%if msg is longer than 0, i.e. it has something in it, we have an error
if length(msg) > 0

  disp('Error opening the file.');

else
  %read the header info
  [width,height,fps,startpos,NumberFrames] = readheader(fid);

  if start < NumberFrames & stop < NumberFrames

     %Now we can read the given frames.
      i=1;
      for frame = start:stop
          %now read the required frame
          y(i,:,:)=readyframe(fid,width,height,startpos,frame);
          i=i+1;
      end
  end
end
fclose(fid);

function [width,height,fps,startpos,NumberFrames]=readyuvheader(fid)

%********************************************************
%This function will read the header of a bath yuv
%
% This file is used by readheader and should not be
% used on its own.
%
% N.Young
% 5 June 2001
%********************************************************

%we should have 1 null character for yuv now
fscanf(fid,'%c',1);

%Now read the width of the sequence
width='';
while ne(width,0)
  width = [width fscanf(fid,'%c',1)];
end

width = str2num(width);

%Now read the height of the sequence
height='';
while ne(height,0)
  height = [height fscanf(fid,'%c',1)];
end

height = str2num(height);

%Now read the fps
fps='';
while ne(fps,0)
  fps = [fps fscanf(fid,'%c',1)];
end

fps = str2num(fps);

%Finally, caluclate the number of frmes in the sequence
startpos = ftell(fid);  %get the current position (should be the start of the data)

fseek(fid,0,'eof'); %move to the end of the file
endpos = ftell(fid);

% now we can calculate the number of frames
FileLength = endpos-startpos;
FrameSize = width * height * 1.5; %quick HACK
NumberFrames = FileLength / FrameSize;

%Reset the file to the start of the data
fseek(fid,startpos,'bof');

function [y,u,v]=readframe(fid,width,height)

%read the required frame from the stream

elements = width*height;

%The reshape below turns the data we read in into 2d data and rotates it.

%read the y frame
[y,count] = fread(fid,elements,'uchar');

%if count is 0, then we have reached the end of the file
if count==0
    y=[];
    u=[];
    v=[];
else
    y=reshape(y,[width,height])';

    %read the u frame, remember this is 1/4 of the size of the y
    u = fread(fid,elements/4,'uchar');
    u=reshape(u,[width/2,height/2])';

    %read the v frame, remember this is 1/4 of the size of the y
    v = fread(fid,elements/4,'uchar');
    v=reshape(v,[width/2,height/2])';
end

function s = yuv2pgm(filename,startframe,stopframe)

%********************************************************
%Funtion to read in a yuv sequence, to memory and
%convert it to a series of pgm images at the same time
%
%Syntax : Y_Sequence = yuv2pgm(filename,startframe,stopframe);
%
%This will read the first n frames from the given sequence,
%and also save pgm copies to, frame0.pgm, frame1.pgm and so on,
%
%NOTE: The frames are numbered from 0.
%
% A.N.Evans & N.Young
% 5 June 2001
%********************************************************

%Read the y frames of the sequence
[width,height,y]=readyseq(filename,startframe,stopframe);

a = 'frame';
c = '.pgm';

%Note, You may not have the 'saveimg' file on your copy of matlab,
% in which case you will have to get a copy of matts 'pgmwrite'.

for i=1:stopframe-startframe+1
   b=[int2str(i+startframe-1)];
   saveimg(squeeze(y(i,:,:)),strcat(a,b,c));
%   pgmwrite(squeeze(y(i,:,:)),strcat(a,b,c));
end
s=y;

NOW A m file thats not a function, just to test the code works. This is saved as demo.m

%Sample yuv file reading

%Read the y frames 0 to 2 of the sequence test.yuv
y = yuv2pgm('test.yuv',0,2);

%the above will also have save 3 pgm files:
%
% frame0.pgm
% frame1.pgm
% frame2.pgm


frame0 = squeeze(y(1,:,:));
frame1 = squeeze(y(2,:,:));
frame2 = squeeze(y(3,:,:));

%show the frames
figure;
image(frame0);
colormap(gray(256))

figure;
image(frame1);
colormap(gray(256))

figure;
image(frame2);
colormap(gray(256))

So after all that i now type in the command window demo
The output is as follows

??? Error using ==> mrdivide
Matrix dimensions must agree.
Error in ==> readyuvheader at 49
NumberFrames = FileLength / FrameSize;
Error in ==> readheader at 48
  [width,height,fps,startpos,NumberFrames] = readyuvheader(fid);
Error in ==> readyseq at 26
  [width,height,fps,startpos,NumberFrames] = readheader(fid);
Error in ==> yuv2pgm at 19
[width,height,y]=readyseq(filename,startframe,stopframe);
Error in ==> demo2 at 4
y = yuv2pgm('test.yuv',0,2);

So now I change the description of FrameSize by changing it from width*height*1.5 by replacing width and height with the dimensions of a cif or Qcif format video.

Now i get this command

>> demo
File format is : YUV 4:2:0
??? Error using ==> fseek
Invalid offset.

Error in ==> readyframe at 16
fseek(fid,startpos + (frame * yuvElements),'bof');

Please Help

Many Thanks in Advance