Low framerate when using Videomixer

[Lukas Middelberg]

Hi,

I would like to use a videomixer element to mix to sources of video 
together.
For some reason, the video becomes really laggy and drops to framerates 
under 1 fps.

This is my pipeline:
gst-launch-1.0 ximagesrc ! \
    queue ! \
    mixr. \
    \
    wrappercamerabinsrc ! \
    queue ! \
    mixr. \
    \
    videomixer name=mixr framerate=30 ! \
    theoraenc ! \
    oggmux ! \
    filesink location={TEMPFILE} sync=true

Additionally, when piping the output into an ximagesink element instead 
of encoding and
writing it to a file, I get these messages:

gstbasesink.c(2846): gst_base_sink_is_too_late (): 
/GstPipeline:pipeline0/GstXImageSink:ximagesink0:
There may be a timestamping problem, or this computer is too slow.

This is definitely not an issue of CPU power. I can use both
"ximagesrc ! fpsdisplaysink"
and
"wrappercamerabinsrc ! fpsdisplaysink"
without any lags or frame drops.

What am I doing wrong?

Cheers,
Lukas