VideoReader read gets progressively slower

I'm using VideoReader in R2013b to read frames from an xvid video file. It gets progressively slower the more frames it reads. Why is this. I put tic and toc around the 'read' command and got this. The larger the frame number the longer it takes. Could I convert to a different video format that won't result in this problem?

Elapsed time is 0.030412 seconds. Elapsed time is 0.031585 seconds. Elapsed time is 0.039171 seconds. Elapsed time is 0.034544 seconds. Elapsed time is 0.053199 seconds. Elapsed time is 0.049999 seconds. Elapsed time is 0.043578 seconds. Elapsed time is 0.069764 seconds. Elapsed time is 0.052462 seconds. Elapsed time is 0.080845 seconds. Elapsed time is 0.076437 seconds. Elapsed time is 0.069285 seconds. Elapsed time is 0.077616 seconds. Elapsed time is 0.065248 seconds. Elapsed time is 0.067999 seconds. Elapsed time is 0.074150 seconds. Elapsed time is 0.081200 seconds. Elapsed time is 0.082125 seconds. Elapsed time is 0.086064 seconds. Elapsed time is 0.086792 seconds. Elapsed time is 0.090830 seconds. Elapsed time is 0.094100 seconds. Elapsed time is 0.095743 seconds. Elapsed time is 0.102189 seconds. Elapsed time is 0.100912 seconds. Elapsed time is 0.105056 seconds. Elapsed time is 0.127760 seconds. Elapsed time is 0.116694 seconds. Elapsed time is 0.115046 seconds. Elapsed time is 0.126171 seconds. Elapsed time is 0.123077 seconds. Elapsed time is 0.145319 seconds. Elapsed time is 0.127868 seconds. Elapsed time is 0.135925 seconds. Elapsed time is 0.136943 seconds. Elapsed time is 0.142427 seconds. Elapsed time is 0.190107 seconds. Elapsed time is 0.161109 seconds. Elapsed time is 0.151043 seconds. Elapsed time is 0.152178 seconds. Elapsed time is 0.153753 seconds. Elapsed time is 0.167216 seconds. Elapsed time is 0.164124 seconds. Elapsed time is 0.165329 seconds. Elapsed time is 0.165570 seconds. Elapsed time is 0.169328 seconds. Elapsed time is 0.190058 seconds. Elapsed time is 0.217986 seconds. Elapsed time is 0.271494 seconds. Elapsed time is 0.278628 seconds. Elapsed time is 0.284078 seconds. Elapsed time is 0.292255 seconds. Elapsed time is 0.220524 seconds. Elapsed time is 0.201130 seconds. Elapsed time is 0.197329 seconds. Elapsed time is 0.216730 seconds. Elapsed time is 0.208506 seconds. Elapsed time is 0.209435 seconds. Elapsed time is 0.243505 seconds. Elapsed time is 0.229380 seconds. Elapsed time is 0.222015 seconds. Elapsed time is 0.230163 seconds. Elapsed time is 0.243643 seconds. Elapsed time is 0.242045 seconds. Elapsed time is 0.237107 seconds. Elapsed time is 0.245758 seconds. Elapsed time is 0.248198 seconds. Elapsed time is 0.276591 seconds. Elapsed time is 0.314398 seconds. Elapsed time is 0.261610 seconds. Elapsed time is 0.295378 seconds. Elapsed time is 0.286336 seconds. Elapsed time is 0.264035 seconds. Elapsed time is 0.274385 seconds. Elapsed time is 0.328306 seconds. Elapsed time is 0.288166 seconds. Elapsed time is 0.321604 seconds. Elapsed time is 0.291431 seconds. Elapsed time is 0.295859 seconds. Elapsed time is 0.315024 seconds. Elapsed time is 0.317039 seconds. Elapsed time is 0.347607 seconds. Elapsed time is 0.337959 seconds. Elapsed time is 0.319575 seconds. Elapsed time is 0.303298 seconds. Elapsed time is 0.298656 seconds. Elapsed time is 0.303022 seconds. Elapsed time is 0.306631 seconds. Elapsed time is 0.311747 seconds. Elapsed time is 0.316540 seconds. Elapsed time is 0.321053 seconds. Elapsed time is 0.328235 seconds. Elapsed time is 0.320567 seconds. Elapsed time is 0.324301 seconds. Elapsed time is 0.335527 seconds. Elapsed time is 0.336781 seconds. Elapsed time is 0.351301 seconds. Elapsed time is 0.342081 seconds.

Answer 1

[Saurabh]

Hi @Peter Bone,

The issue arises because MATLAB's 'read()' method in older R2013b with compressed formats is not indexed. Each call to 'read(v, i)'causes MATLAB to rescan the file from the start or the nearest key‑frame. As the frame number grows, this scanning becomes progressively slower.

To resolve the issue there are few workarounds which can be opted:

• Switch to 'readFrame()' (R2014a and newer): readFrame() reads sequentially and avoids per-call scans, tracking position internally.

while hasFrame(v)
  frame = readFrame(v);
  % process frame
end

• Preload All Frames Once: If memory allows, read all frames at once to build an indexed array:

frames = read(v, [1 Inf]);
% then access frames(:, :, :, i) quickly

• Convert Video to Indexed Format (e.g. .seq, Uncompressed AVI) : Convert to a format with a frame index table for fast random access. MATLAB supports .seq (via MathWorks example) or uncompressed AVI for quicker seeking.

Choosing one of these options- especially moving to 'readFrame()' or converting the video format-will eliminate progressive slowdowns and improve frame access effciency.

I hope this helps in resolving the query.