Custom Gst.Element in GTK3

[Manuel]

Custom Gst.Element in GTK3
--------------------------
Hi all,

I wrote a gst.Element (GTK2), which is a simple filter that just
forwards all buffers it receives on the sink-pad to the src-pad. Later I
will grab some information from the buffer before forwarding it. (More
precisely I will grab the timestamps and show some text based on the
time, like subtitles). The GTK2-version works fine.

Today I tried to change my code so that it uses the GTK3
gi.repository-package.
Although the new class looks almost the same it doesn't work.

This is the error printed on the console:
Error: Internal error: can't allocate images xvimagesink.c(979):
gst_xvimagesink_show_frame ():
/GstPlayBin:MultimediaPlayer/GstPlaySink:playsink/GstBin:vbin/GstBin:timed-video-bin/GstAutoVideoSink:autovideosink0/GstXvImageSink:autovideosink0-actual-sink-xvimage:
We don't have a bufferpool negotiated

Here is my GTK2-version: http://pastebin.com/J2gHfvS4
And here the GTK3-version: http://pastebin.com/9u8zzcTk

This is a scenario:
A video-file is played using playbin. The playbin's video-sink is set to
a Gtk.Bin that combines my own Gst.Element with textoverlay and an
autovideosink.

NOTE: If you remove the textoverlay from the GTK3 example then at least
the audio is playing ;)

I would be very grateful for your help. :)

Best Regards