You just about covered it. Content flagged as PSF can be treated by a display device capable of progressive display as progressive. Its carried in fields for compatability with interlaced systems. Which is why PSF exists.
Progressive content as interlaced not flagged as PSF won’t be handled as progressive by displays that can handle progressive display and indeed you will suffer interference between field updates.
Pat Horridge
Broadcast & Post Consultant, Trainer, Avid Certified Instructor
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pat@vet.co.uk