Upgraded to Catalina - all QT videos now wont work

Apple doesn’t “approve” or recommend any third party app per se, but us users here might be able to suggest what we think are excellent converter apps.

• I like ff·Works, a GUI for ffmpeg, which can convert about any video or audio to almost any other format.
• I can also easily recommend HandBrake, a free and easy-to-use converter app (with handy presets), that can take just about any input, and export to .mp4 or .mkv. (I think it is also based on the excellent ffmpeg libraries.) No tinkering required, but you can if you want to.

NO WARNING and NO ADVICE

The end of 32 bit apps for macOS had been announced years in advance, and was heavily publicized.

Googling alternatives took me to Elmedia

That says more about their marketing budget than their quality. It is not on my recommendation list.

Good of you to find this forum, though. Less marketing, more honesty.

It is confusing that the version of QT that works on Mac OS Sonoma is also termed QT 10.5 - only the build code is different.

I agree. They also differ enough to warrant a different version number, imho, even if the differences are in the deeper layers of the framework. But they didn’t ask me.

People will have to specify both OS version and QTP version, else file compatibility is near meaningless.

May I ask you do you think VLC Version 4 when it comes will work on Mac OS Catalina 10.15 please.

Impossible to say. Even VLC themselves might not know at this time. I suppose they will offer support as far back as can easily be done in their software development; that is in their best interest. Alternatively, often older versions stay available for who needs that for their older systems.