How to process large video in Matlab with for loop and without memory error

Question

I\'m new to Matlab processing, and I would like to read and process a large video (more than 200k frames) inside a \"for loop\" (or without it). In particular, i would like

Answer 1

% create video handle and get number of frames
vidObj = VideoReader(video_file);
nFrames = get(vidObj, 'NumberOfFrames');

blocksize = 1000;
BlocksIDs = 1:blocksize:nFrames;
nBlocks = numel(BlocksIDs);

frame_step = 3;

% cell array with all correlations values grouped by block
xcorrs_all_blocks = cell(1, nBlocks);

for j = 1 : nBlocks

    % if this is the last block, process until the last frame
    if j == nBlocks
        last_frame = nFrames;
    % otherwise, read until next block
    else
        last_frame = BlocksIDs(j + 1);
    end
    % compute the frame numbers that we want to look at
    frame_indices = BlocksIDs(j) : frame_step : last_frame;
    nFrames = numel(frame_indices);

    first_frame = [];
    % pre-allocate array holding the in-block corr2 values.
    xcorrs_this_block = nan(1, nFrames-1);

    for k = 1 : nFrames

        % read-in raw frame from video file.
        raw_frame = read(vidObj, frame_indices(k));            
        % determine level for bw conversion - this might help.
        level = graythresh(raw_frame);
        raw_frame = im2bw(raw_frame, level);

        if k == 1
            % save current frame as first frame for later corr2 processing
            first_frame = raw_frame;
        else
            % calc the correlation between the first frame in the block and each successive frame
            xcorrs_this_block(k-1) = corr2(first_frame, raw_frame);
        end


    end

    % save all xcorr values into global cell array.
    xcorrs_all_blocks{j} = xcorrs_this_block;

end