[winswitch] record audio via pulseaudio with xpra?

[Massimiliano Dal Cero]

Hi all,
when run a xpra environment with this command:

$ xpra start-desktop :2020 --start="fluxbox" --start="xrandr -s
1280x720x16" --no-daemon --bind-tcp=0.0.0.0:14500 --html=on
--resize-display=no --encoding=h264 --speaker=on --start="google-chrome"

I can hear the sound on the remote client (via html5 client).

Also, on the "server" I can record screen with ffmpeg, but without audio
(second pulseserver is running, but is recognized only the main pulseserver
of the system).

$ ffmpeg -f x11grab -video_size "1280x720" -framerate 25 -i :2020.0 -f
pulse -i 1

So, my question now is:
how can i record both screen and audio?

Thanks a lot & best regards :)
Max