vsViewer reveals problem with vapoursynth.so (I think)

[drfear]

Still on the trail of testing plugins but I have yet to get past first base ...

I've installed vsViewer from github, but when I run it (standalone) it shows, as I would expect, just two lines of code

import vapoursynth as vs
core = vs.core

and then, unexpectedly, a red error message

2024-01-20 15:59:02.574
Failed to initialize VapourSynth environment!
Failed to initialize VapourSynth environment!

If I run those two code lines in a console python session, there is no complaint, however, see what happens with the 4th code line below:

>>> import vapoursynth as vs
>>> vs
<module 'vapoursynth' from '/home/myname/opt/vapoursynth/lib/python3.11/site-packages/vapoursynth.so'>
>>> core = vs.core
>>> core
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "src/cython/vapoursynth.pyx", line 2750, in vapoursynth._CoreProxy.__repr__
  File "src/cython/vapoursynth.pyx", line 2715, in vapoursynth._CoreProxy.core.__get__
  File "src/cython/vapoursynth.pyx", line 2701, in vapoursynth._get_core
  File "src/cython/vapoursynth.pyx", line 2705, in vapoursynth.vsscript_get_core_internal
  File "src/cython/vapoursynth.pyx", line 2681, in vapoursynth.createCore
vapoursynth.Error: Failed to obtain VapourSynth API pointer. System does not support SSE2 or is the Python module and loaded core library mismatched?

(By the way, the problem is definitely not due to lack of SSE2, checked that with 'cat /proc/cpuinfo | grep flags' just to be sure.)

This seems like it might be related to a problem relating to passing pointers as integers reported as fixed a few years ago, https://github.com/vapoursynth/vapoursynth/issues/468 but I am completely baffled.  Also, if it is actually a bug in the source code of vapoursynth, why doesn't everyone in the world have the same problem?

I've tried compiling with both system and local Cython 3.0.8-1 - no difference.

On the plus side, this would explain why absolutely none of my plugin testing has been successful so far :-)

Any clues?