High latency with my JPEG VAAPI pipeline

[Wolfgang Grandegger]

Hello,

I'm trying to understand the latency figures measured with a smartphone
and camera for the following pipeline:

  # gst-launch-1.0 -v udpsrc port=5678 buffer-size=2000000 do-timestamp=1 \
     caps="application/x-rtp, media=(string)video, clock-rate=(int)90000, encoding-name=(string)JPEG, payload=(int)26, framerate=(fraction)30/1" \
     ! rtpjitterbuffer latency=5 \
     ! rtpjpegdepay \
     ! vaapijpegdec \
     ! vaapisink

I measure around 130 ms. The latency trace with "GST_TRACERS=latency
GST_DEBUG=GST_TRACER:7" is reporting src to sink latencies of just
around 40 ms:

  0:00:08.447955233   411       0x4d3c00 TRACE             GST_TRACER :0:: latency, src-element-id=(string)0x4f03a0, src-element=(string)udpsrc0, src=(string)src, sink-element-id=(string)0x51acc0, sink-element=
(string)vaapisink0, sink=(string)sink, time=(guint64)41801197, ts=(guint64)8447919094;
  0:00:08.481356539   411       0x4d3c00 TRACE             GST_TRACER :0:: latency, src-element-id=(string)0x4f03a0, src-element=(string)udpsrc0, src=(string)src, sink-element-id=(string)0x51acc0, sink-element=
(string)vaapisink0, sink=(string)sink, time=(guint64)41875079, ts=(guint64)8481323375;
  0:00:08.514592194   411       0x4d3c00 TRACE             GST_TRACER :0:: latency, src-element-id=(string)0x4f03a0, src-element=(string)udpsrc0, src=(string)src, sink-element-id=(string)0x51acc0, sink-element=
(string)vaapisink0, sink=(string)sink, time=(guint64)41766241, ts=(guint64)8514557403;

I wonder what is responsible for the 90 ms extra latency. Of course, the
camera and the network introduces some latency, but if I use MPV
instead,

  # mpv --profile=low-latency --untimed jpeg.sdp

I measure just 80 ms. Still a difference of 50 ms. Any idea where that
comes from?

TIA,

Wolfgang