So, a glue layer for

* (LAN-)devices, most a source/sink/control for various Audio/Video streams.

* Those devices (can) share/use any HW (Microphones/Speakers/V4L-devices) available

* programs producing/consuming sound/video, to be "exported" as individual sinks/sources

* Eventing support to dynamically change media routing

Your stated "reference problem" (Car AV) is (imho) not the most user-"relatable" scenario (after all, who has "hackable car"), a more common scenario I'd see:

* In several of the rooms of the dwelling there are

* Devices large/small with several connection types

  * LAN (PCs, TVs, AV-HW, MediaPlayers, ...) with protocols including e.g.

    * Well-known programs (VLC, KODI) with their "own" protocol

    * UPNP/DLNA/AirPlay/Miracast/PulseAudio/RTSP/...

    * SIP/WebRTC devices/clients (Doorbells, VoIP-Phones, VideoConf)

    * Devices with Vendor-specific protocols. e.g LG WebOS

  * USB connection to one of the above (WebCam, Android-devices, phones)

  * Wifi-P2P (Some of LAN devices have this too, for e.g. screencasting)

  * Bluetooth BTLE/Classic (devices can be stationary/mobile/transient)

I would like to enable these usecases: * Send [emulated] [second] screen from PC to any Display surface

* View any desktop/UI/program/device on any other display surface

* Control all the above from PCs/Phones/Tablets, or Events (Doorbell -> Camera PiP @TV)

* Route any audio/video source to my speech-recognition/video-conf/VoIP Software

* Use Android device [connected to USB[ of another Device]] as 8+ devices: Camera F/R, Screen I/O, Audio I/O Headphone/Speaker/BT Microphone/App-Output

* Use "hook"-scripts for eventing/device control (TV might need some command to switch to HDMI3)

I realize most of the above can be probably be done using some GST/FFMPEG glue scripts/code and some systemd dependencies, but I'm haven't found quickly relatable examples of: * "Run this command/config to add an ffpmeg commandline as virtual camera"

* "Use this config to represent your TV as another display output device"

* "Run this command On DevA to launch a GUI-binary on DevB, and make this "stream" available as VideoSource in Browser@DevA"

* "Use the Webcam on DevA, bluetooth headsets via DevB for input, TV1 as VideoOutput, AudioOut on AVR, runnings VideoConf on DevC"

* "Do this to implement access-control" (Bob can see Input "foo", but Alice can't)