How do I extract frames iteratively?

So far I have been able to trim the video and went from 4007 frames to 1509 frames, from those frames I only want to get every 3rd frame starting from the first. Currently I only know how to trim the video and to check how much frames the video has not much else.

[Daniel Mendoza Hermosillo]

% Import video file
obj = VideoReader('D:\Spring 2022\MARS Capstone\Trimmed Videos\Reef 1\GH010063.MP4');
vid = read(obj);
% Read the total number of frames
frames = obj.NumFrames;
% File format of the frames to be saved
ST = ' .jpg';
% Reading and writing the frames
for x = 1 : frames
    % Converting integers to string
    Sx = num2str(x);
    % Concatening 2 string 
    Strc = strcat(Sx, ST);
    vid = vid(:, :, :, x);   
    % Exporting the frames
    imwrite(vid, Strc);   
end

this is a code i found online that helps me write the frames into images that I can use later but it stops because it needs 23.2 GB storage to run, so I wanted to reduce the number of frames that I pick up from this code.

Answer 1

[Walter Roberson]

% Import video file
obj = VideoReader('D:\Spring 2022\MARS Capstone\Trimmed Videos\Reef 1\GH010063.MP4');
% File format of the frames to be saved
ST = ' .jpg';
% Reading and writing the frames
i = 1;
while hasframe(obj)
    % Converting integers to string
    Sx = num2str(x);
    % Concatening 2 string 
    Strc = strcat(Sx, ST);
    vid = readframe(obj);
    % Exporting the frames
    imwrite(vid, Strc);
    i = i + 1;
end

[Daniel Mendoza Hermosillo]

Thank you for your answer, just curious would this help me get every 3rd frames or would it export all 1509?

[Walter Roberson]

% Import video file
obj = VideoReader('D:\Spring 2022\MARS Capstone\Trimmed Videos\Reef 1\GH010063.MP4');
% File format of the frames to be saved
ST = ' .jpg';
% Reading and writing the frames
x = 0;
while hasframe(obj)
    vid = readframe(obj);
    x = x + 1;
    if mod(x, 3) ~= 1; continue; end
    % Converting integers to string
    Sx = num2str(x);
    % Concatening 2 string 
    Strc = strcat(Sx, ST);
    % Exporting the frames
    imwrite(vid, Strc);
end

It is also possible to ask to read() a particular frame by frame index, but I suspect this code would be faster.

[Daniel Mendoza Hermosillo]

Thank you this is what I was looking for