For the "why PDF?", Vol 0 of the zine was discussed on HN earlier this year (413 comments): https://news.ycombinator.com/item?id=27880905

There's also Vol 2, which is a PDF/A document that also parses as text/gemini: http://lab6.com/2

The last one has interesting discussion on the future of information archiving.

You could probably embed a video stream the same way --- as the name implies, streaming formats are specifically designed so that it's not necessary to find the "start" or "end" of the stream, but instead sync markers with a distinctive pattern are present at regular intervals so readers can just look for those and begin decoding.
i was in a FaceTime call when i opened this in Chrome on iOS.

The speakerphone became max volume and the volume slider became unresponsive.

i had to open up another media player and play music to get the volume slider to work again

> 250e3f7d581acff115537ba38e89ad31 is a handy random 128-bit integer that will appear in every issue of Lab 6 and can be used to search for copies.

I really like this idea for uniquely identifying emails. Our shop had been messing with something similar, but had trouble bridge the gap between the lay people and the technical minded people.

I feel like poc||gtfo already has done the pdf polygot thing to perfection...
It’s been ~18 months and nobody’s made much progress on the CTF hidden in the first issue as far as I can tell!
this is so cool