NTP wall clock time of first frame in captured MP4 file

[kmliu]

I have a pipeline like this to capture H.264 video from an RTSP camera to an
MP4 file:

gst-launch-1.0 rtspsrc location=rtsp://xxx ! rtph264depay ! h264parse !
mp4mux ! filesink location=camera.mp4

I want to get a very accurate wall clock time that the first frame in the
MP4 file corresponds to. This needs to be more accurate than just reading
the system time when I start the pipeline. I can sync the camera to an NTP
clock. The camera is supposed to send an NTP-to-RTP timestamp mapping in its
RTCP Sender Report. From this, gstreamer should know the NTP wall clock time
of the first frame. But how do I extract this information from gstreamer?



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