Saving gray images to .avi with VideoWriter and Lagarith codec

highgui

asked 2015-04-21 10:52:20 -0600

lb
11 ●3

updated 2015-04-23 03:56:16 -0600

I wish to save grayscale images to a (small) avi file with the Lagarith codec under Windows in a 32 bit application compiled with Visual C++ 2010 and OpenCV 2.4.10. I'm using the VideoWriter object from highgui. However, the function VideoWriter::open returns false --see the following code snippet:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>
using namespace cv;

int main(int argc, char* argv[]){
    VideoWriter outputVideo;
    if (!outputVideo.open("test.avi", CV_FOURCC('L', 'A', 'G', 'S'), 25.0, Size(800, 600), false))
        std::cout << "Couldn't open VideoWriter" << std::endl;
}

Is this the expected behaviour? I could convert my gray image to a color image but as far as I know the Lagarith codec compresses each channel separately so I think it would increase the size of the resulting video. How can I get the smallest possible video file?

Edit:

Encoding color images works.
I compiled OpenCV in debug mode and it seems Video For Windows is being used for compression.

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answered 2015-04-22 11:22:22 -0600

Eduardo
3589 ●1 ●15 ●41

updated 2015-04-22 11:25:48 -0600

"How can I get the smallest possible video file?"

You can use a lossy codec (Lagarith is a lossless codec) like CV_FOURCC('M','J','P','G').

OpenCV use ffmpeg for reading / writing videos. I think there is some kind of problem between OpenCV and the ffmpeg library used when the OpenCV dll was built, that's why it returns 0 ? Or maybe ffmpeg can decode Lagarith but not encode in Lagarith ?

If you want to keep a lossless video, one option could be to save the images in a directory (img_1.png, img_2.png, etc.) using a lossless format like png and after use a tool to create a video from images like ffmpeg.

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Thanks for your answer! From executing OpenCV in Debug mode it seems Video For Windows is used internally. Encoding color images is OK. Saving the images as png could be a good workaround but I leave the question open to see if there are other options.

lb ( 2015-04-23 04:01:01 -0600 )edit

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answered 2016-09-18 14:47:09 -0600

Alfonso Perez-Escudero
1

Hi!

I was also unable to make the Lagarith codec only work with grayscale images (maybe it's prepared for color images only?).

I use the following workaround: for every three grayscale frames in the video, I stack them creating a false color image. Then I save this image using the Lagaryth codec.

Of course, this solution is not good if you want a standard video player to reproduce your video. In my case I just want to archive the images in compressed format, and read them from another script.

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Saving gray images to .avi with VideoWriter and Lagarith codec

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