I followed your suggestion. It actually seemed to be working as it did it’s thing on this large file over the course of a couple of hours, but in the end it failed to repair the file.
Regarding file size, I do recall seeing it as an 861 mb file, perhaps when it was in its AVCHD state in the cam, before it transferred into its unusable 32 gb state.
Anyway, tks for your attempt to help me.