Invalid buffer timestamp; dropping buffer?

[pisymbol .]

I have a multistage pipeline that looks like this:

gst-launch-1.0 -v -e matroskamux name="muxer" streamable=true !
multifilesink post-messages=true next-file=5 max-file-duration=60000000000
location=capture.mkv \
  nvcamerasrc fpsRange="30.0 30.0" aeLock=true sensor_id=0 \
  ! 'video/x-raw(memory:NVMM), width=(int)4104, height=(int)3046,
format=(string)I420, framerate=(fraction)30/1' \
  ! nvvidconv flip-method=3 ! 'video/x-raw(memory:NVMM), width=(int)1520,
height=(int)2704, format=(string)I420' \
  ! omxh264enc bitrate=10000000 ! 'video/x-h264,
stream-format=(string)byte-stream' ! h264parse ! muxer.video_0 \
  nvcamerasrc fpsRange="30.0 30.0" aeLock=true sensor_id=1 \
  ! 'video/x-raw(memory:NVMM), width=(int)4104, height=(int)3046,
format=(string)I420, framerate=(fraction)30/1' \
  ! nvvidconv flip-method=3 ! 'video/x-raw(memory:NVMM), width=(int)1520,
height=(int)2704, format=(string)I420' \
  ! omxh264enc bitrate=10000000 ! 'video/x-h264,
stream-format=(string)byte-stream' ! h264parse ! muxer.video_1

Basically, I'm trying to capture streams from two cameras and mux them into
one mkv file. This works on the command line and I can view the capture
without issue.

However, when I try to import this into PyGst using
parse_from_description() I don't get any output at all! I also don't get
any explicit errors either. Instead I see this continuously:

0:00:03.297571465 11548   0x7f800021e0 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_0> Invalid
buffer timestamp; dropping buffer
0:00:03.298439263 11548   0x7f84003b20 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_1> Invalid
buffer timestamp; dropping buffer
0:00:03.310016224 11548   0x7f800021e0 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_0> Invalid
buffer timestamp; dropping buffer
0:00:03.317109682 11548   0x7f84003b20 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_1> Invalid
buffer timestamp; dropping buffer
0:00:03.340857644 11548   0x7f800021e0 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_0> Invalid
buffer timestamp; dropping buffer
0:00:03.348889524 11548   0x7f84003b20 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_1> Invalid
buffer timestamp; dropping buffer
0:00:03.376322341 11548   0x7f800021e0 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_0> Invalid
buffer timestamp; dropping buffer
0:00:03.377022270 11548   0x7f84003b20 WARN             matroskamux
matroska-mux.c:3558:gst_matroska_mux_write_data:<muxer:video_1> Invalid
buffer timestamp; dropping buffer

I'm not sure how to debug this. Googling suggests this is a latency issue
but I don't see that could be since gst-launch-1.0 again works fine.
Somewhere something got lost in translation.

NOTE: I've already set do_timestamp=true for the nvcamerasrc to no avail.

Any suggestions?

-aps
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