But I actually like it. The idea is that I can pass -c or -m to my script and it's a meaningfully different playlist order (either plays in the order I downloaded, or the order the videos were originally uploaded)

And yes the videos were downloaded with youtube-dl

edit: ohhh it uses the Last-modified HTTP header to set the mtime!! cool! https://unix.stackexchange.com/questions/387132/youtube-dl-a...