Halt video transmission on bad connection

I used to have conversations with a partner who's mobil connection is a) slow and b) bad, so there's a high latency and a high rate of package drops.

This sometimes leads to having to extremely low fps at the video transmission and even worse to robotic sounding voices and eventually to a call drop.

I know from WhatsApp that they stop the video transmission and replace the background image with the last received picture and an overlay saying "video halted", when the connection quality falls under a certain level.

Further I know, that for example with Mumble and the Opus codec we never had any trouble understanding each other nor we had participant drops.

Summary

1. Somehow measure the current connection quality.
2. If the value of 1) falls under a certain level: a) stop video transmission b) lower bitrate and/or bandwidth if voice transmission
3. adjust 2) if the quality becomes significantly better again.

Setup

Nextcloud Talk v3.1.1 on Android 7.1.2
Nextcloud 15.0
Stun/Turn-Server: Yes

The issue names no files or tests. Start by locating the Android Talk call media and connection-quality handling, then determine how quality thresholds, video pausing, the last received image, and voice bitrate changes should work; done means degraded connections preserve understandable audio and recover video when quality improves.