input-selector => flvmux: create audio clicks/pops/artefacts when switching input

[blokfyuh]

I have 2 Nvidia Jetson Nano on my local network, each one running their own
gstreamer pipeline. On the first one (i.e. the slave), the pipeline looks
like this:

gst-launch-1.0 -e v4l2src ! 'video/x-raw,width=(int)1920,height=(int)1080' !
videoconvert ! videorate ! 'video/x-raw,framerate=(fraction)30/1' !
nvvidconv ! 'video/x-raw(memory:NVMM),width=1920,height=1080' ! omxh264enc !
flvmux streamable=true ! rtmpsink
location=rtmp://MASTER_LOCAL_IP/live/CAMERA_ID
So it's a simple pipeline that take a USB camera input, encode it in h264,
mux it and send it to a nginx rtmp server on the second Jetson Nano.

On the second Jetson Nano (i.e the master), the pipeline looks like this:

gst-launch-1.0 -e v4l2src ! queue !
'video/x-raw,width=(int)1920,height=(int)1080' ! videoconvert ! videorate !
'video/x-raw,framerate=(fraction)30/1' ! nvvidconv flip-method=0 top=0
left=0 bottom=1080 right=1920 !
'video/x-raw(memory:NVMM),width=(int)1920,height=(int)1080' ! omxh264enc
bitrate=4000 ! "video/x-h264" ! h264parse ! input-selector
cache-buffers=true sync-streams=true sync-mode=1 name=i ! queue ! flvmux
streamable=true name=mux ! rtmpsink location=rtmp://random/rtmp/server/url
rtmpsrc location=rtmp://SLAVE_LOCAL_IP/live/CAMERA_ID flvdemux ! queue ! i.
alsasrc device=hw:2,0 ! queue ! audioconvert ! audioresample !
audio/x-raw,rate=44100 ! voaacenc bitrate=192000 ! "audio/mpeg,
mpegversion=4" ! aacparse ! queue ! mux.

It's a more complex pipeline. It takes a USB camera input, encode it in h264
and send it to an input-selector. It also retrieve the rtmp stream from the
slave, demux it and send it to the input-selector. It also retrieve the
audio from an alsa device and encode it in AAC. Then the input-selector
output and the audio are muxed and sent to a remote RTMP server.

FYI, my real code use the Python Gstreamer API, but for the sake of this
question, I translated my python code into those gst-launch commands.

In my python code, I have some logic that switch the active-pad of the
input-selector every 5 seconds, to either get the master input source or the
slave one.

While the pipeline is running on the master Nano, I get a lot of flvmux
errors:

flvmux gstflvmux.c:1082:gst_flv_mux_buffer_to_tag_internal:<flvmux:sink_0>
Got backwards dts! (0:25:45.133000000 < 0:25:45.234000000)
And every 2x(swich time period) = 10s, I get this error:

v4l2src gstv4l2src.c:976:gst_v4l2src_create:<v4l2src0> lost frames detected:
count = 10 - ts: 0:28:18.428984294
This error below is perfectly periodic. If I change the switch time period
and put it at 15 seconds for example, I will get this every 30 seconds (i.e.
2x15s).

And all those errors messages have the effect to produce a lot of audio
clicks/pops when I listen to it on the remote RTMP server. If I don't switch
the input-selector, I don't get those glitches.

I have been working on this issue for weeks without any luck.

Any help would be appreciated. Thanks.



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