How to read video file stored in structure?

Question

amit pathania 2012-2-11

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编辑： Matt J 2013-10-8

I am trying to process a video file,i am able to read and store it in a structure.But i am not able to read values from structure to process and play it. My code is like this:

    vid = Video Reader('sample.avi');
    nframes= vid.NumberOfFrames;
    vidHeight = vid.Height;
    vidWidth = vid.Width;
    halfframes=round(nframes/2);
   mov(1:halfframes) = struct('cdata',zeros(vidHeight, vidWidth, 3, 'uint8'),'colormap', []);
      %to read the frames and store it in structure   
     for k = 1:halfframes 
        mov(k).cdata = read(vid,( 2*k -1));
    end
  %till here its working fine
  %if i try to read values by using a loop its not working
      for k = 1:halfframes 
          frame= mov(k).cdata 
          imshow(frame);
      end

this loop is not working and i am not getting all images/frames please help me with this

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Answer 1

Walter Roberson 2012-2-11

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A) There have been some reports that VideoReader is skipping frames and repeating frames, with the incidence of that perhaps higher for variable frame-rate files.

B) put a drawnow() after the imshow().

C) If you have the image processing toolkit, you may wish to consider using implay rather than looping displaying the frames yourself.

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Walter Roberson 2012-2-11

Note by the way that NumberOfFrames is not meaningful for a variable-frame-rate video until after the video has been read to the last frame.

Side note: you do not need to initialize the zeros for mov(k).cdata. The read() you are doing will construct new storage and will use that storage, discarding any storage already allocated for mov(k).cdata . Might as well just initialize it to a single 0.

amit pathania 2012-4-12

Hi,

I am just reading a video file and for faster processing want it to store in structure first.But,it's not showing it in a loop.I can view them individually but not in loop

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Answer 2

amit pathania 2012-2-11

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thanks Walter, but i need to process these frames by carrying out few image processing operations and then display processed image in GUI axes. Can you suggest me the solution?