It would be useful, if Xpra would show the currently used video encoding and video encoder in {System Tray > Session Info > Connection}, similar to how the codec is displayed for "Speaker".
This cannot be done, especially since version 2. There is no "current encoding".
The "auto" encoding is the default and it will select the best encoding available for any given region. Video regions may get encoded with any of the available video encodings, same for the non-video regions which may use any of the non-video encodings - all concurrently.
If you want to inspect this visually, use the opengl client with Meta+Shift+F12
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1561