GStreamer hangs with v4l2src, compositor, tee and fakesync

Terry Barnaby terry1 at
Tue Nov 9 08:26:58 UTC 2021

Hi, I wonder if anyone can point me to where I am going wrong ?

I am working on an embedded video system and have a solid video stream 
lockup on the pipeline start. I have reduced the problem to a 
gst-launch-1.0 command line that fails under Fedora33 (as well as 
Fedora29 and Centos8-stream) with default gstreamer packages installed. 
When I run the following I see a glimagesink window with the contents of 
the test1.png file displayed but no video stream from the webcam 
(Logitec C920 USB). I should see the test1.png overlaying the video stream.

If I remove the "t. ! fakesink sync=false" part it runs fine (this would 
normally go to further processing). I have also seen lockups with a 
similar setup using videotestsrc rather than v4l2src intermittently.

gst-launch-1.0 -v compositor name=c sink_1::alpha=1.0 ! videoconvert ! 
glimagesink  v4l2src ! jpegdec ! queue ! tee name=t  t. ! queue ! 
c.sink_0  t. ! queue ! fakesink sync=false multifilesrc 
location=./test1.png caps=image/png,framerate=1/1 ! pngdec ! imagefreeze 
! videoconvert ! c.sink_1

Any ideas ?

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