Combine two videos and place than side by side gstreamer

side_by_side

gst-launch-1.0 \
    videomixer name=m sink_1::xpos=50 sink_1::ypos=50 sink_2::xpos=400 sink_2::ypos=50  \
    ! x264enc \
    ! rtph264pay \
    ! udpsink host=localhost port=5000 \
    videotestsrc pattern=white \
    ! video/x-raw, format=I420, framerate=5/1, width=740, height=480 \
    ! m. \
    videotestsrc pattern=red \
    ! videobox left=100 \
    ! video/x-raw, format=I420, framerate=5/1, width=300, height=200 \
    ! queue \
    ! m. \
    videotestsrc pattern=green \
    ! videobox left=500 \
    ! video/x-raw, format=I420, framerate=5/1, width=300, height=200 \
    ! queue \
    ! m.

Nice