"decreasing DTS value" error with `nleurisource`s

[amindfv at mailbox.org]

A more general version of this question is how does one play a clip, then play another clip, writing the whole thing out to a single file?

I asked a variation on this question a few weeks ago, and I was pointed towards `nleurisource`, but now it seems like I'm having similar clock issues with `nleurisource` too.

A high-level description is fine: I'm comfortable adding pad probes, doing pipeine manipulation, etc. A link to docs or example code would be a great help.

Thanks,
Tom

On Fri, Jul 22, 2022 at 01:35:00AM -0700, amindfv--- via gstreamer-devel wrote:
> I'm attempting to write a .mp4 file made up of 4 clips from other videos. I'm using `nleurisource` to play a portion of a file, then when it's done I remove that `nleurisource` and create a new one for the next clip, until they're all done.
> 
> Before trying to write to a file, I had a version which output to `autovideosink`. That worked great. When I use x264enc->mp4mux->filesink, though, I get errors like this:
> 
> 
> 0:00:02.340877233 968227      0x47bae40 ERROR                  qtmux gstqtmux.c:4711:gst_qt_mux_add_buffer: decreasing DTS value 0:00:00.000000000 < 0:00:02.760000000
> 0:00:02.355170406 968227      0x47bae40 ERROR                  qtmux gstqtmux.c:4711:gst_qt_mux_add_buffer: decreasing DTS value 0:00:00.040000000 < 0:00:02.760000000
> ...
> 0:00:02.987386018 968227      0x47bae40 ERROR                  qtmux gstqtmux.c:4711:gst_qt_mux_add_buffer: decreasing DTS value 0:00:02.560000000 < 0:00:02.760000000
> 0:00:03.025097697 968227      0x47bae40 ERROR                  qtmux gstqtmux.c:4711:gst_qt_mux_add_buffer: decreasing DTS value 0:00:02.600000000 < 0:00:02.760000000
> 
> 
> This seems to be occurring for the 2nd, 3rd, and 4th videos. It appears, then, that creating a new `nleurisource` is resetting a clock to zero somewhere, and the file encoding is getting messed up because of it?(i.e. the 1st video caused the clock to count up to ~2.76, and then it didn't like when the 2nd video reset the clock to zero?)
> 
> If I only try and write 1 clip instead of 4, it of course works fine.
> 
> Am I correctly diagnosing the issue? And more importantly, how can I fix it?!
> 
> (Note I'm specifically asking how to do this with `nleurisource` or segment seeking. I'm aware of `ges-launch` and other tools but for a variety of reasons I need more fine-grained control.)
> 
> Thanks!
> Tom