I am on Debian/sid, using latest G’MIC version from github.
Here are the results and the conclusion I have reached.
This command failed for me in the past too, which held me back then from looking into g’mic any further. Perhaps you have lost more people interested into this in the past.
Here is a detailed list of what I found.
The file is an emacs org file with the org extension replaced with txt to make the upload possible.
Yes, this is clearly related to a video output issue. I’ve tested the same script here on my Ubuntu 16.04, and it works as expected: it produces a .mov file that I can read with mplayer.
To read/write video files, G’MIC relies on OpenCV’s routines, and it seems that in your case the codec ‘MP4V’ is undefined, and unfortunately, this is the default video codec used in G’MIC.
Maybe you can try changing the codec, like this: