I'm wondering if it's possible to do content filtering in a firewall. Maybe with something that cooperates with pf. I'm on a very limited (5 GB/month) metered internet connection through a cell phone and I'm not the only user when I have it shared over wifi. I'd like to block video because it's an incredible waste. Problematic clients are Android/Kindle. User competence in not clicking where they shouldn't is sometimes an issue.
I can see this happening if there's a file size available during transfers, if the size is under a certain threshold value it just passes without interference, over a certain size the first few bytes of the file get checked. If it fails the check that exact URL to the file would get blacklisted for maybe 24 hours. I've noticed watching random transfers with wget that in some cases it knows the file size from somewhere and sometimes not. Presumably there's no size available on streaming video so just block it. There seems to be an abundance of video in advertising in apps but also in news apps there's a mix of video and text stories. Most of the world assumes bandwidth is free and fast. Some videos are bigger than entire operating systems, and most are fairly pointless. If the transfer is happening over an ssl connection maybe not much can be done since from the firewall's perspective it's just encrypted data, essentially inside a tunnel.
