As reported in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785859
xpra currently still depends on GStreamer 0.10.
GStreamer 0.10 is no longer maintained and supported by the upstream project since almost 3 years, and contains many known bugs that are fixed in the new 1.x release series of GStreamer. Next to many bug fixes, the new release series also contains many other improvements, new features and a more streamlined API.
For the next Debian release GStreamer 0.10 is planned to be removed.
As of 0.16, it will be possible to run gstreamer 1.x with the GTK2 code: See ticket:849#comment:9
Though this is unlikely to be the default at this point.
Before opening this ticket I had a look at #849 but I did not recognised it as duplicate due to broader scope of the problem. We have (at least) few years ahead of us till next Debian release so hopefully there is enough time to address this...
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/903