Raspberry Pi Low-Latency Stream with GStreamer

[Matteo Valdina]

Hi
Do you really need gdpay? The RTP should be enough.

About your tee element you need to add queue element after the tee.
About the latency the queue element need some tweak for lowering the
latency but if your latency is 150 ms is good.

Best
Matteo


On Oct 26, 2017 04:52, "Gary Thomas" <gary.thomas at piksel.com> wrote:

I suggest you add queue elements downstream from the tee. I do something
similar with RPi and the receive pipeline I use is:

gst-launch-1.0 tcpclientsrc host=pizero1 port=5000 ! gdpdepay !
rtph264depay ! h264parse ! tee name=parsed parsed. ! queue ! avdec_h264 !
autovideosink sync=false parsed. ! queue ! mpegtsmux ! filesink
location=cam.ts

Gary

-----Original Message-----
From: gstreamer-devel [mailto:gstreamer-devel-bounces at lists.freedesktop.org]
On Behalf Of waymond91
Sent: 26 October 2017 08:52
To: gstreamer-devel at lists.freedesktop.org
Subject: Raspberry Pi Low-Latency Stream with GStreamer

Hello All!
I am trying to setup a raspberry pi as a low latency network camera (max.
latency 200ms).
In an ideal world, the raspberry pi would read the camera, send it over
wifi to a host pc.
This host PC would both display the video stream and save it to a file.
A key aspect that I am really struggling with is:
I would like the displayed image to be saved to a file that included a
timestamp of when an individual frame was actually displayed.
That being said, this is my first time doing any video processing
whatsoever.
I was able to find and build a gstreamer source for the pi camera from the
git repository here:
https://github.com/thaytan/gst-rpicamsrc

This seems to work. With the raspberry pi I am able to start a network
pipeline with the following command:
*$ gst-launch-1.0 rpicamsrc bitrate=1000000 \
    ! 'video/x-h264,width=640,height=480' \
    ! h264parse \
    ! queue \
    ! rtph264pay config-interval=1 pt=96 \
    ! gdppay \
    ! udpsink host=[MY IP] port=5000*

And on my host PC I can display a live stream with about 150mS latency with:
*$ gst-launch-1.0 udpsrc port=5000 \
    ! gdpdepay \
    ! rtph264depay \
    ! avdec_h264 \
    ! videoconvert \
    ! autovideosink sync=false*

Or save the stream with:
*$ gst-launch-1.0 udpsrc port=5000 \
    ! gdpdepay \
    ! rtph264depay \
    ! avdec_h264 \
    ! videoconvert \
    ! filesink location=video.h264*

So I am beginning to feel like I am on track.
Ultimately, however, I feel like I need to decode the h264 into some other
format (MP4?) so that I can actually start displaying and saving individual
frames and associating them with the current time (or at the least the time
between frames).
At the very least, I would like to be able to save and display the h264
stream with one pipeline.

On my host side, I have tried a tee element like so:
*$ gst-launch-1.0 udpsrc port=5000 \
  ! gdpdepay \
  ! rtph264depay \
  ! avdec_h264 \
  ! videoconvert \
  ! tee name = t \
  t. ! autovideosink sync=false \
  t. ! filesink location=tee.h264*

However, the video stream freezes up shortly after initialization. Any
ideas of how I can fix this?
Any ideas of how I can save the decoded, displayed frames and the time it
was displayed? I don't mind doing a little post-processing to get this
lined up correctly :P Any ideas on how to cut latency?

Thanks again for the help!
PS Sorry I couldn't get code tags to work...



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