mp4mux complains about missing PTS

Florian Echtler floe at
Tue Apr 18 11:42:05 UTC 2023

Hello everyone,

I'm trying to record multiple H.264 and Opus streams to a MP4 file. However, 
there is apparently some sort of race condition going on, because in roughly 8 
out of 10 attempts, the pipeline fails with the following error and an EOS:

gst-stream-error-quark: Could not multiplex stream. (10): 
../gst/isomp4/gstqtmux.c(5402): gst_qt_mux_add_buffer (): 
Buffer has no PTS.

In the other 20% of cases, the pipeline starts and the resulting MP4 file 
contains all the streams, correctly synchronized and playable. I also tried with 
qtmux instead of mp4mux, but got the same results.

I'm attaching the dot graph for the failure case; the dot graph for a successful 
run looks exactly identical, with the only difference being that the filesink 
doesn't flag EOS.

Side question: even if everything works, the resulting MP4 file is not seekable. 
Is there a straightforward fix for that?

Thanks and best, Florian
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