Hi,
Please refer to
$ gst-launch-1.0 nvcompositor name=mix sink_0::xpos=0 sink_0::ypos=0 sink_1::xpos=0 sink_1::ypos=240 ! 'video/x-raw(memory:NVMM)' ! nvvidconv ! video/x-raw ! textoverlay text="hello" ! nvvidconv ! 'video/x-raw(memory:NVMM)' ! nvoverlaysink videotestsrc ! nvvidconv ! mix.sink_0 videotestsrc ! nvvidconv ! mix.sink_1