Processing Frames from a Video

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Hollis Williams
Hollis Williams on 15 Apr 2022
Commented: David K. on 15 Apr 2022
I have a piece of code where I read an image and then do some processing with it. If I instead have an AVI file, is there a simple way to read the video file, select a chosen frame from it, and then analyse that frame as an image?
III0 = double(imread('Documents\sphereattempt.png'));
III1 = (III0(:,:,3)./(III0(:,:,1)+III0(:,:,2)+III0(:,:,3)));
figure(2);
contourf(flipud(min(max(movmean(movmean(III1,10,2),10,1),0.3),0.5)),[0.3:0.01:0.5]);
axis equal;
colorbar
set(gca,'Ydir','reverse')

Accepted Answer

David K.
David K. on 15 Apr 2022
The VideoReader object looks like the way to go. With the basic case being:
v = VideoReader('example.avi');
while hasFrame(v)
frame = readFrame(v);
% processing for each frame goes here
end
Where frame is an individual image. If you want to start from a specific time you can use
v.CurrentTime = 2.5; % time in seconds to start
then use readFrame to get the frame you want.
Something that may go wrong is shown on Supported Video Formats where there is a troubleshooting section talking about how there is a chance that you will need to install some other things if your specific avi format is not currently readable by your matlab install. I have not personally tried any of these methods to fix a format issue.
  2 Comments
David K.
David K. on 15 Apr 2022
Not quite. The readFrame function is taking the place of the imread function in your code. If the video is X by Y pixels and is in color. The output frame from
frame = readFrame(v);
should be a X x Y x 3 uint8 array. So III0 should be
III0 = double(readFrame(v));
to make them the same as your single image.

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