gst-launch-1.0 -v glvideomixerelement name=m sink_1::xpos=300 sink_2::ypos=400 sink_3::xpos=300 sink_3::ypos=400 ! glimagesink \
gltestsrc ! glupload ! gltransformation rotation-y=45 ! m. \
gltestsrc ! glupload ! gltransformation rotation-y=45 ! m. \
gltestsrc ! glupload ! gltransformation rotation-y=45 ! gldownload ! videocrop ! glupload ! m. \
gltestsrc ! glupload ! gltransformation rotation-y=45 ! gldownload ! videocrop ! glupload ! m.