<div dir="auto"><div> <div class="gmail_quote"><div dir="ltr" class="gmail_attr">Le mar. 18 févr. 2020 10 h 45, Wolfgang Grandegger <<a href="mailto:wg@grandegger.com">wg@grandegger.com</a>> a écrit : </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello, still hunting latency! When I use "vaapisink sync=false" the latency drops from 130 ms to 60 ms. There seem to be a kind of backlog somewhere. Any idea how that could happen or be avoided. Is there a tracer showing buffer/queue usage? </blockquote></div></div><div dir="auto"> </div><div dir="auto">I would investigated why the depaylaoder reports that 80ms. For this use case, you should use the fast start on the JB too, it should remove the 100ms start-up latency, and most likely drops at start.</div><div dir="auto"> </div><div dir="auto"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Thanks, Wolfgang Am 09.02.20 um 19:07 schrieb Wolfgang Grandegger: > Hello, > > thanks for your valuable input... > > Am 07.02.20 um 14:01 schrieb Nicolas Dufresne: >> On ven, 2020-02-07 at 12:26 +0100, Wolfgang Grandegger wrote: >>> 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 >> >> What method to you use to measure this ? > > I put my Android smartphone close to the display. On the smartphone I > start the clock app and start the timer. Then I place the camera in > front, recording both, the smartphone screen and the display. Then I > take a picture with my compact camera and compare the times shown on > the picture. I think that's what you name "glass to glass" latency. > >>> GST_DEBUG=GST_TRACER:7" is reporting src to sink latencies of just >>> around 40 ms: >> >> You should look at the reported latency, maybe we are reporting too much. For >> this do: >> >> GST_TRACERS="latency\(flags=pipeline,element,reported\)" > Hm, what does "GST_TRACERS="latency" report? I think for the "flags=" I > need 1.6.x, IIRC. > >> To view the results, I suggest using gst-stats-1.0 tool form the latency logs >> saved to filed. >> >> pipeline ... 2> trace.log >> gst-stats-1.0 trace.log > > OK, here is what I get. I have added some comments/questions with (*): > > # gst-stats-1.0 /tmp/trace.log > > Overall Statistics: > Number of Threads: 0 > Number of Elements: 0 > Number of Bins: 0 > Number of Pads: 0 > Number of GhostPads: 0 > Number of Buffers passed: 0 > Number of Events sent: 0 > Number of Message sent: 0 > Number of Queries sent: 0 > > (*) Shouldn't the numbers above show some real values? > > Time: 0:05:54.100866710 > > Latency Statistics: > 0x4ef650.udpsrc0.src|0x5193a0.vaapisink0.sink: mean=43415981 min=38730503 max=108822660 > > (*) The 43 ms seem to be the src to sink latency similar to what > "GST_TRACERS=latency" reports. > > Element Latency Statistics: > 0x4f5db0.rtpjitterbuffer0.src: mean=54507945 min=21104 max=107217916 > > (*) Why is the rtpjitterbuffer responsible for most of the latency? > > 0x503fc0.rtpjpegdepay0.src: mean=340660 min=85865 max=655983 > 0x51eba0.vaapidecode_jpeg0.src: mean=1123497 min=282112 max=108139722 > > Element Reported Latency: > 0x4ef650.udpsrc0: min=0 max=0 ts=0:00:00.183949148 > 0x4f5db0.rtpjitterbuffer0: min=5000000 max=18446744073709551615 ts=0:00:00.184021844 > > (*) Does this very high max value screw up the statistis? > > 0x503fc0.rtpjpegdepay0: min=0 max=0 ts=0:00:00.184053451 > 0x51eba0.vaapidecode_jpeg0: min=80000000 max=0 ts=0:00:00.184074524 > > Some of the figures above a really confusing. > >> Depending on the display rate, and considering you likely have a compositer, >> you'll have about 1.5 vblank latency duration added to your glass to glass >> latency. vaapisink maybe use more HW blocks, so there might be some latency >> added there too (I'm not too wail informed on tha taspect). > > The display runs at 60 Hz, hence 25 ms vblank latency. I'm using X11 and > the Matchbox Window manager. Can I avoid or improve the vblank latency > somehow? The latency is not really better if I use "kmssink" (without > X11). > >> There is an extra 15ms added in the vieo sink, see processing-deadline. In your >> case, I assume it should have 33ms latency + processing time, so you have about >> 7ms of processing time. >> >>> >>> 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? > > Still puzzled why "mpv" does a much better job here (50 ms less latency!). > > Wolfgang > _______________________________________________ > gstreamer-devel mailing list > <a href="mailto:gstreamer-devel@lists.freedesktop.org" target="_blank" rel="noreferrer">gstreamer-devel@lists.freedesktop.org</a> > <a href="https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel" rel="noreferrer noreferrer" target="_blank">https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel</a> > > _______________________________________________ gstreamer-devel mailing list <a href="mailto:gstreamer-devel@lists.freedesktop.org" target="_blank" rel="noreferrer">gstreamer-devel@lists.freedesktop.org</a> <a href="https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel" rel="noreferrer noreferrer" target="_blank">https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel</a> </blockquote></div></div></div>