The version 0.31.4 didn't work with the previous version of Opera. It did work with the latest 54.0.2952.51 version.
That does make me wonder if the problem is more than just the wrong code being distributed.
Yes, a new lib doesn't work with previous releases, but a previous lib can work with new Opera releases. With new Opera releases many changes inside the code is done, fixes are made so the libffmpeg has to accommodate this changes that is some time incompatible with previous releases of Opera , it has nothing to do with wrong coding.
I think we may be slightly mixed up.
1: Why can't Opera work properly without getting a library-file from somewhere else? That suggests that, as distributed, it is supplied with the wrong code.
2: If the library has to be specially made to work with the opera calls, that feels as though the Opera code is badly written. It's missing the whole point of a library.
The first error should be easy to fix. The second feels a rather deeper problem.