GStreamer Python bindings are effectively GPL

While most of the bindings are LGPL licensed, modules like pygst are licensed under the terms of the GPL-2+. This means, together with the fact that you need to use pygst for any application wishing to use these binding, that you can not create proprietary or non-GPL-compatible programs using the GStreamer Python bindings.

You can read more about this in the Debian Bug Tracker in Bug#516190. I expect that this should be forwarded to upstream but I haven’t checked their bug tracker yet.