Pipeline blocking when part of an mp4mux is not receiving data

[Wayne Piekarski]

Hi everyone,

I have a use case where I'm recording a V4L H264 camera along with a UDP 
audio stream into an mp4mux file, and also displaying the video to the 
screen.

gst-launch-1.0 -v \
mp4mux name=combo fragment-duration=1000 ! fakesink async=false \
\
v4l2src 
device=/dev/v4l/by-path/pci-0000:00:14.0-usb-0:2:1.0-video-index1 
do-timestamp=false ! video/x-h264, width=320, height=240, framerate=15/1 
! h264parse ! tee name=tv0 ! queue ! h264parse ! avdec_h264 ! 
videoconvert ! autovideosink    tv0. ! queue ! combo.video_0 \
\
udpsrc port=5701 do-timestamp=false ! application/x-rtp, 
clock-rate=44100, config=40002410adca00 ! rtpmp4adepay ! aacparse ! 
queue ! combo.audio_1

This works fine if there are UDP packets coming in. However, if the UDP 
source has not sent any packets, then the video stops displaying on the 
screen after about 50 frames of working fine.

However, if you send just one valid RTP packet to the port, then 
everything starts working, and stays working, even though no new UDP 
packets are arriving.

Is there anyway to tell the pipeline to not block like this? I tried 
putting async=false everywhere as recommended to me in 
https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/issues/628 but 
that is not working in this new scenario. I've tested this on the latest 
gstreamer 1.16.0.

thanks!