"Dot indexing is not supported for variables of this type." error in reading VideoReader Object by its index?

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INDRANATH ROY
INDRANATH ROY on 5 May 2022
Answered: yanqi liu on 7 May 2022
I am working in video shot boundary detection, for that I need to read a specific video frame by its index, But in such cases when the video is read by its index in the main file, it runs perfectly but when it is ran in a seperate function, It gives an error "Dot indexing is not supported for variables of this type. in matlab", I am providing the code for which it is givning the error.
V=VideoReader("anni007.mpg");
if class1(1)>2
A=final(class1,V); % class1 is a frame transition numbers
else
class1 = class1(2:length(class1));
A=final(class1,V);
end
function A2 = final(C,V)
count = 1; th1 = 0.2; th2 =1;th3= 1;
for i = 1:length(C)
St = StdDifference(V,C(i));
if (St(2) > th1 && St(3)< th1 && St(1) < th1)
A2(count) = C(i);
count = count + 1;
end
end
end
function d = StdDifference(V,i)
count = 1;
for j=i-2:i+1
I = read(V,j);% This line the code gives error of "Dot indexing is not supported for variables of this type" I cannot understand why?
J = read(V,j+1);
Ir_std = std2(I(:,:,1));
Ig_std = std2(I(:,:,2));
Ib_std = std2(I(:,:,3));
Jr_std = std2(J(:,:,1));
Jg_std = std2(J(:,:,2));
Jb_std = std2(J(:,:,3));
d(count) = sqrt((Ir_std-Jr_std)^2+(Ig_std-Jg_std)^2+(Ib_std-Jb_std)^2);
count = count + 1;
end
end
  5 Comments
Walter Roberson
Walter Roberson on 5 May 2022
If the VideoReader call failed then that read() might be the first place affected.
Also I wonder if there is additional code beyond what was posted, with that additional code happening to have a "clear all"

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Answers (1)

yanqi liu
yanqi liu on 7 May 2022
yes,sir,may be use VideoReader to make video to frame image file list,and then use the images to analysis,such as
function nFrames = GetVideoImgList(videoFilePath)
xyloObj = VideoReader(videoFilePath);
nFrames = xyloObj.NumberOfFrames;
vidHeight = xyloObj.Height;
vidWidth = xyloObj.Width;
[pathstr, name, ext] = fileparts(videoFilePath);
video_imagesPath = fullfile(pwd, sprintf('%s_images', name));
if ~exist(video_imagesPath, 'dir')
mkdir(video_imagesPath);
end
files = dir(fullfile(video_imagesPath, '*.jpg'));
if length(files) == nFrames
return;
end
h = waitbar(0, '', 'Name', 'process...');
steps = nFrames;
for step = 1 : nFrames
temp = read(xyloObj, step);
temp_str = sprintf('%s\\%04d.jpg', video_imagesPath, step);
imwrite(temp, temp_str);
pause(0.01);
waitbar(step/steps, h, sprintf('%d%%', round(step/nFrames*100)));
end
close(h)

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