getframe not updating when outputting video/images

Question

Brian 2014-7-21

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/142779-getframe-not-updating-when-outputting-video-images

评论： Chad Greene 2014-7-21

采纳的回答： Brian

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Hello, thanks for reading this,

I have a image that I'm outputting to a gif/avi video, and neither one seems to work.

When I use the code:

    lseg = getframe(h);
    set(gcf,'InvertHardCopy','off')
    imwrite(lseg.cdata, outputFileName, 'WriteMode', 'append');
    camorbit(1, 0, 'data', [0 0 1])
    drawnow

and see my image stack, they're all the same image: the lseg frame never gets updated when I rotate with camorbit. Additionally, when I try to make a video with:

    fps = 60; sec = 10;
    vidObj = VideoWriter('newfile.avi');
    vidObj.Quality = 100;
    vidObj.FrameRate = fps;
    open(vidObj);
    for i=1:fps*sec
      camorbit(0.9,-0.1);
      writeVideo(vidObj,getframe(gcf));
    end
    close(vidObj);

I get a 10 second video of a static frame: again, getframe never gets updated to the frame rotated by camorbit.

When I view the image as its writing, I can see the figure rotating. Its just when MATLAB writes to file, the written file frames are not updated.

Any ideas?

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Brian 2014-7-21

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Actually, I got the video export to work by including the line

drawnow

after camorbit.

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Answer 1

Brian 2014-7-21

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https://ww2.mathworks.cn/matlabcentral/answers/142779-getframe-not-updating-when-outputting-video-images#answer_145851

Use drawnow after camorbit and it works.

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Answer 2

Chad Greene 2014-7-21

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https://ww2.mathworks.cn/matlabcentral/answers/142779-getframe-not-updating-when-outputting-video-images#answer_145832

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I've had troubles with getframe in the past. I've had better luck using export_fig . The syntax would be

frame = export_fig(gcf); 
writeVideo(vidObj,frame);

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Brian 2014-7-21

Just a update, I manually switched the axis to a value, and while it ran a bit longer, I wasn't able to get a full 360 degree turn, it stopped midway.

Why would the resolution of the movie suddenly change?

Chad Greene 2014-7-21

I think you'd need the -nocrop option in export_fit. That's because by default export_fig crops the frame to the dimensions of where plotted objects appear on the figure. If some data being plotted in your figure starts to go near the edge of the frame, export_fig will increase need to increase the size of the frame. Using the -nocrop option prevents the automatic frame sizing.

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