Playback of a video stream is slow under GTK

[pisymbol .]

Pipeline:
filesrc location=\"{}\" ! matroskademux name=demux demux.video_{} !
h264parse ! avdec_h264 ! videoconvert name=videoconvert

Obviously 'demux_video_{}' is calculated at run-time (usually 0 or 1).

When I use this within a GTK application, i.e. I connect 'videoconvert'
connect to 'gtksink' the video looks like it is in slow motion.

Has anyone seen this before?

-aps
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