After Gstreamer 1.16.3, seeing CPU starvation in pipline containing GESTimeline

[David Ing]

I am running Gstreamer on Windows, MSVC; and I'm seeing the same problem on
Fedora Linux.

Basically I have a GstPipeline which contains a GESTimeline and then some
encoders.  When the pipeline runs under Gstreamer 1.16.3, I typically reach
100% CPU usage (which is what I want).  But under Gstreamer 1.18.4, it is
more like 40% CPU usage (and the job takes longer).

The encoders are third party elements which are always the same (in both
conditions), so I am ruling those out.  It seems like it must be the
gstreamer elements (perhaps within the GESTimeline).

*My questions are*:

   1. Does anyone know of some changes (perhaps related to threading) that
   might be causing this issue?
   2. What is a good way to diagnose this problem?

I have some files on a gfolder here
<https://drive.google.com/drive/folders/1b-jGZUw0g7RvwormxZcThKSxF3zdLK5e?usp=sharing>
to illustrate the problem.

   - *cpu_under_utilization.png* shows CPU usage over time:
      - The first bump is the pipeline running under Gstreamer 1.16.3
      -
      - The next bump is the pipeline running under Gstreamer 1.18.4
   - *playing_1.16.3.svg* shows the pipeline on 1.16.3
   -
   - *playing_1.18.4.svg* shows the pipeline on 1.18.4 (it looks the same).
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