Add WebRTC features (camera, screen and window sharing)

[stweil]

Many modern web browsers now support HTML5 and WebRTC, features which could be very useful for users of PalMA, too.

Currently, screen sharing requires special software (VNC) for the notebook with screen sharing. It is limited to sharing of the whole screen. Sharing of a single window is not supported. Screen sharing is unsupported for iOS and Android devices.

With WebRTC it is no longer necessary to install special software on the client's side. WebRTC can share a single window or the whole screen. Maybe it even works with iOS and Android.

WebRTC also allows sharing of camera live images and audio, so PalMA could even be extended to be used as a web conference platform.

[stweil]

Maybe the implementation can be based on SimpleWebRTC which is also used for Nextcloud Talk.

[jmechnich]

Python-based API which might be useful: https://github.com/aiortc/aiortc

[dennmuel]

An alternate approach could be Deskreen: https://github.com/pavlobu/deskreen
Users could paste the resulting link into the URL field in PalMA so as to have chromium display the shared screen. Unforunately, this is not (yet?) available for Android or iOS. Also, I'm not sure if this will work across different subnets...