Using VideoWriter for imagesc

I would like to make a movie based on imagesc(M), where M is a matrix that changes with t in a loop. Of course, any other solution that outputs a video file with the frames of what is shown by imagesc would also be fine. Here's what I have:

%looping over t
h = imagesc(M);
axis off
refreshdata(h,'caller')
drawnow
F(t) = getframe(gcf);

%outside loop
v = VideoWriter('newfile.avi','Archival');
v.FrameRate = 60;
open(v)
writeVideo(v,F)
close(v)

However, I get the warning:

Warning: No video frames were written to this file. The file may be invalid. 
> In VideoWriter/close (line 267)
  In VideoWriter/delete (line 202)
  In Untitled (line 44) 
Error using VideoWriter/writeVideo (line 369)
The 'cdata' field of FRAME must not be empty

Error in Untitled (line 47)
writeVideo(v,F)

Thanks!

[Varshini Guddanti]

I tried to change the order of your code. Please try this:

% outside loop

v = VideoWriter('newfile.avi','Archival');

v.FrameRate = 60;

open(v)

.

% inside loop
.

%looping over t

h = imagesc(M);
axis off

refreshdata(h,'caller')

drawnow

F(t) = getframe(gcf);

writeVideo(v,F)

% close loop

.

% outside loop

close(v)

Answer 1

[Walter Roberson]

Is it possible that you store one final frame after the end of the t loop, and that final frame is empty? Or alternately, that you store an empty initial frame?

For debugging, add this before the VideoWriter:

all_valid = true;
flen = length(F);
for K = 1 : flen
  if isempty(F(K).cdata)
    all_valid = false;
    fprint('Empty frame occurred at frame #%d of %d\n', K, flen);
  end
end

if ~all_valid
   error('Did not write movie because of empty frames')
end

[Daniele Bernardo Panaro]

Hello I have a similar problem. Using your debugging code (adapting it to my code) it gives me the message

'Empty frame occurred at frame #1 of 1139

Error using UP_MGL_1_2 (line 239)

Did not write movie because of empty frames'

How do I fix the empty frame?

Thank you

[Walter Roberson]

I notice that only the first frame is empty, not the others. That hints that you might have an off-by-one error in the logic of how you store the frames. Could you show us the code you use to initialize your frame array, and how you update it?