Here is a letter from TMD Hosting support - they were very kind but couldn't help. Its a UNA issue they say. Help! I must have configured something wrong but I don't know what it could possibly be.

Hello,

Thank you for your patience up to now.

We have thoroughly reviewed your concern and would like to inform you that we were able to recreate the issue from our end.

We have tried to resolve the issue which you are currently experiencing with your website but regrettably, all attempts were unsuccessful.

However, according to our investigations, the UNA script uses the build-in ffmpeg and not the server's one, therefore the issue is related directly to the bug of UNA cms since the server meets all requirements as could be verified via Dashboard - Server Audit

The executable ffmpeg file is located in ....

Here is the video conversion log:

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We would recommend you contact the vendor and developers of the UNA cms who should be able to review this and provide you with additional information, as unfortunately, this is out of our area of expertise as a hosting provider.

Thank you for understanding and do not hesitate to contact us again if we could be of any further assistance!

Best Regards,

Roy Herman

Technical Support Team