| The way these video meeting services work is the participants all connect to the service's servers. Each participant sends their video feed to the server, which sends it on to the other participants in the meeting. It's that server that wants to be able to dynamically downgrade outgoing feeds based on the bandwidth between it and the meeting participants, which can vary from participant to participant. Alice, for example, might be on a symmetric gig fiber connection with consistent and low latency. Her client can send a high resolution feed to the server. Bob might have no trouble with receiving that, but Carol might be on slower, less stable connection, and need a lower resolution version. If you aren't trying to do E2E encryption, you can handle this by having the server deal with taking the high resolution feed from Alice and generating a low resolution feed and then sending the other participants whichever is the best version they can handle. That works because without E2E encryption the server actually has access to the video, so it can do things like resample and re-encode. If you are using E2E though then the only parties that should have access to the video itself are the meeting participants. The server should not have access to the video except in encrypted form. The problem then is how to encode and encrypt a video stream in such a way that a server that is copying that stream between a sender and one or more recipients can alter a copy of the stream in such a way as to reduce the resolution even though it does not have access to unencrypted video? |