Comment # 6 on bug 1161548 from Wolfgang Bauer

These errors could occur if the clips in the project use codecs not supported
by the installed ffmpeg libraries.
Maybe the reporter didn't install the Packman versions, but the clips are
encoded in formats not supported by openSUSE's versions for legal reasons...

The AppImage probably includes its own (full-featured) copies that made it
work.

FWIW, I quickly created a simple project right now with Leap 15.1's kdenlive
18.12.3 (18.04 might have been a typo) and tried to load it in the latest
19.12.1 (self-built branch from the KDE repos), no problems here.
Then I switched ffmpeg and libav* to the standard openSUSE versions, and I got
the same error dialog.

-> For me this bug report seems to be invalid.
The reporter should add the Packman repo and do a full switch to it (as usual
for multimedia stuff).

But let's wait for a response a little more.