capture to file, A/V out of sync

[Katerina Voulgary]

Hello, I have a pipeline that does not synchronize audio with video. It 
seems like it has captured less audio than video.

VLC plays both streams synchronized, but stalls the video (still frame) 
at the beginning. MPlayer plays both streams immediately, but audio lags 
(~1 second).

I start gstreamer from a bash script for two cameras like this, both 
files have the same problem,perhaps one more than the other:

        (gst-launch-1.0 -e pulsesrc device=${audio_array[0]} ! 
audio/x-raw, rate=8000, channels=2 ! queue !  opusenc name=aenc0 
audio-type=voice bitrate-type=cbr bandwidth=narrowband ! queue 
max-size-buffers=0 max-size-bytes=0 max-size-time=5000000000 ! 
mux0.audio_0 v4l2src device=/dev/${camera_array[0]} ! videoconvert ! 
queue ! x264enc name=enc0 tune=zerolatency ! queue ! matroskamux 
name=mux0 ! queue ! filesink location=1$RECORDING_FILEPATH sync=true 
&>/dev/null & ) &
         (gst-launch-1.0 -e pulsesrc device=${audio_array[2]} ! 
audio/x-raw, rate=8000, channels=2 ! queue !  opusenc name=aenc1 
audio-type=voice bitrate-type=cbr bandwidth=narrowband ! queue 
max-size-buffers=0 max-size-bytes=0 max-size-time=5000000000 ! 
mux1.audio_0 v4l2src device=/dev/${camera_array[2]} ! videoconvert ! 
queue ! x264enc name=enc1 tune=zerolatency ! queue ! matroskamux 
name=mux1 ! queue ! filesink location=2$RECORDING_FILEPATH sync=true 
&>/dev/null & ) &

I was tipped for the parametres at queue to compensate for the x264enc 
latency. The project is to capture a determined time accurately I am not 
restricted to container or encoder.

1. Could someone give me directions on how to capture synced 
audio+video? I suspect pulsrc, because I don't know much about it.

2. One camera starts later than the other. Can gstreamer add some 
waiting on the pipeline for both cameras to be ready before it starts 
capturing or it should be handles externally somehow?


GStreamer 1.16.2

Ubuntu 20.04.2 LTS