Image overlay over a video stream

[Wolfgang Grandegger]

Hello,

I'm currently evaluating the following pipeline to receive, display and
record a MJPEG video stream:

  # nice -20 \
    gst-launch-1.0 -v \
    udpsrc port=50004 buffer-size=180000000 do-timestamp=1 \
      caps="application/x-rtp, media=(string)video, clock-rate=(int)90000, \
      encoding-name=(string)JPEG, payload=(int)26, framerate=(fraction)50/1" \
    ! rtpjitterbuffer latency=20 \
    ! rtpjpegdepay \
    ! vaapijpegdec \
    ! timeoverlay \
    ! tee name=t
    t. ! queue ! vaapisink
    t. ! queue ! vaapih264enc ! mp4mux ! filesink location=/tmp/test.mp4

The CPU usage of the various threads with and without the element
"timeoverlay" is listed below:

    with timeoverlay ->  no     yes 
  TID  Thread Name      CPU %  CPU %
  ----------------------------------
  542  gst-launch-1.0    42.0   88.8 
  550  queue0:src         0.2    0.4
  549  vaapiencodeh264    5.3    5.5
  548  gmain              0.0    0.0
  547  udpsrc0:src        8.9    8.4
  546  rtpjitterbuffer    8.5   51.6
  545  timer              0.0    0.0
  544  queue1:src        14.8   17.6
  543  queue0:src         3.9    4.9

The "timeoverlay" adds approx. 45% to the CPU load (max is 4 x 100%).
What does take that much CPU time?
Is there a faster way to do the overlay or is that element from the
Pango plugin already quiet efficient?
I want to overlay an image over the video stream, ideally done by
the graphics hardware.

Thanks for your help,

Wolfgang.