[pthatcherg]

First of all, there are 2 different kinds of video calls: 1:1 and group calls. For 1:1 calls, e2e encryption doesn't cause any problem at all.

For group calls, it depends on how it's implemented, but many group calls are implemented using what's called a Selective Forwarding Unit (SFU) and the sending clients send multiple resolutions (either independent, called "Simulcast" or dependent, called "SVC"). In that case, the adaptation is done by the server in selecting which resolution to forward at any given time. This is fairly common practice in the industry. For example: https://github.com/jitsi/jitsi-videobridge and https://tools.ietf.org/html/draft-aboba-avtcore-sfu-rtp-00 and https://www.w3.org/TR/webrtc-svc/.

For those types of group calls, the server only needs to know the sizes of the various streams and which packet is for what stream. It does not need to see the decrypted media, so one can implement e2e encryption for such types of group calls. This is less common in the industry, but is possible. For example: https://support.google.com/duo/answer/9280240?hl=en

(I used to work at Google on WebRTC, Duo, and Hangouts, but now work on video calling at Signal).

[cbsmith]

That would seem to require significantly more upload bandwidth & compression capacity from clients, which is often not broadly available to consumers. I guess you could drop down to the lowest resolution only when sending to the service if you have a bandwidth challenge, but that seems less than ideal.

[pthatcherg]

Lots of video conferencing systems already work this way (the SFU way). Compared to just sending the full resolution all the time, adding the smaller resolutions doesn't add that much bandwidth and compression because they are so much smaller.

[cbsmith]

Actually I'm calling BS on this. Zoom is literally adjusting frame rates at the single frame per second level. There is definitely upload pressure. SFU isn't going to be enough.

[cbsmith]

But a lot of video conferencing systems are designed for office environments, where you tend to have symmetric bandwidth.