Element/Matrix/Coturn: Computer-to-computer audio/video calls work, computer-to-mobile device calls do not

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1

Problem Description
I am trying to place an audio/video call in Element over my FreedomBox’s matrix-synapse and coturn servers. With computer-to-computer calls, I am able to place them successfully. With computer-to-mobile device calls, the audio and video do not fuction, even if the call connects.
I am using a laptop with Debian 11 Bullseye. Two users I contacted were using computers with what I assume is Windows. I encountered the problem when I tried to contact one of the same users who was using an Android phone over the exact same Internet connection. The only changing factor was the platform of the other user.

Steps to Reproduce

  1. User 1 places call over a laptop in Element to User 2 on a phone. The call connects, but no video is visible and no audio is audible.
  2. User 2 places call over a phone in Element to User 1 on a laptop. The call connects, but no video is visible and no audio is audible.
  3. User 1 places call over a laptop to User 2 on a laptop. Video and audio work well.
  4. User 2 places call over a laptop to User 1 on a laptop. Video and audio work well.
  5. Users are able to type messages to each other, both on computer-to-phone and computer-to-computer.
  6. I cannot test any type of phone-to-phone connection, as I have no mobile device.

Expected Results
I expect the audio and video to function in computer-to-phone calls as they do in computer-to-computer calls.

Actual results
I am able to connect to the other user, but I see only a black screen with the options to hang up, mute the mic, stop the camera, etc. I am able to see my own video feed in the bottom corner, however.

Information

  • FreedomBox version: Latest stable
  • Hardware: FreedomBox Pioneer Edition
2

For clarity, we are on seperate networks in different parts of the world. We are not on the same local network.

3

If indeed it is a case" local calls works and public calls don’t work" thing, then it is similar to this and also this.
In the first case the user had to disable Coturn completely to solve his problem.

Seems that Coturn is not working as it should in both Xmpp and Matrix. If the devs need any help debugging I am here to help.

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