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Matlab VideoWriter is very slow

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timo
timo on 30 Jul 2018
Edited: Jan on 3 Aug 2018
So i am trying to cut an mp4 file , and remove the last 20% I go from start :) and i have this code where 5833 is the last frame i want to write
videoFReader = vision.VideoFileReader('2018-07-30_21h52_48.mp4');
videoFWriter = vision.VideoFileWriter('myFile.avi','FrameRate',...
videoFReader.info.VideoFrameRate);
for i=1:5833
videoFrame = step(videoFReader);
step(videoFWriter,videoFrame);
end
I observed that : 1. My CPU is used around 25% (only one core from 8) 2. the process is very slow - the original file is 45 Mb but 5 minutes passed and is still at 80% done ..
Any workaround to make it faster (use GPU / or multi core ) ? For a professional product this is kinda of embarrassing :(

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timo
timo on 1 Aug 2018
Do you accept the challenge ? If i cannot do it i will pay u 50 bucks.
OCDER
OCDER on 1 Aug 2018
I really do support your efforts to make a multithreaded video WRITER, not multithreaded video processor or reader. VideoWriter is slow for you and others, and you'll be doing yourself and others a favor. The multithreaded video writer would be great - just ignore my skepticism, as that comes from my ignorance.
"for sure you can write from 8 processes in parallel on the hard drive ." "Well i can make a demo where i have a file with..." "If i cannot do it..."
So can you or can you not do it???
"If you pay me 50 bucks i can make the demo... If i cannot do it i will pay u 50 bucks."
No. Why pay you 50 before you make something, and if you fail, you just return (or not return) 50? Sounds unfair.... Plus, it's maybe a violation of forum policy to request money for code/service.
"Content that you submit must be offered free of charge. You may not use the Site to sell or market your products or services to others."
Jan
Jan on 2 Aug 2018
Let's keep the discussion on a professional level.

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Accepted Answer

Jan
Jan on 2 Aug 2018
Matlab is not the perfect tool for cropping MP4 files. Why not let a special tool like ffmpeg do this? See https://www.ffmpeg.org/

  3 Comments

timo
timo on 2 Aug 2018
Finally a sane answer. Thank you and it worked
Dinesh Iyer
Dinesh Iyer on 3 Aug 2018
In 18a, there have been performance improvements made to VideoWriter as per the release notes. Maybe you can give 18a a shot.
timo
timo on 3 Aug 2018
Hello I have latest Matlab

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R2018a