This utility helps concatenate PNG images with non-uniform durations using ffmpeg. Each frame's duration is determined from the difference between the file creation timestamps of the frame and the following one.
In my case this was needed to convert frames dumped from a Py5 program to a (roughly) accurate video, since the recording process drops a lot of frames.
Usage: ./vfconcat <path_glob>
<path_glob>: A glob specification for the frame files, e.g. 'frames/frame_*.png'
The program produces a file named input.txt in the current directory, which lists frames and durations in the format used by ffmpeg's concat demuxer (also see this Stack Overflow answer where I learned about it, and showed that fractional durations can be used).
This convenience script launches ffmpeg using the concat demuxer and the input file produced by vfconcat.