On android I’ve used QR scanner pfa and I recommend it.
If you want to share static video, you could simply share a proton document or google docs. You could use a secure pastebin which does not require account and is not linked to you.
If you want to go to the chat route, Signal and SimpleX chat already have QR generation feature when youre sharing a link to your group.
Not all messengers have the same feature and security. Signal and simplex are user friendly but might not be the top contender if you require a life and death protection. See privacy guide chat section for recommendation.
Do note that with chat, you will also need to moderate, which could be a pain.
I’m reading through the lines here, but If you’re planning to attend a protest, there are guide for that which are more broad than just communication tool, take a look at eff guide for protesters.