[noggin]

Just working off the Mediainfo of the .vob files.
Black Hawk Down movie DVD ISO and its saying 720x576, 25fps, PAL, Interlaced. Unless its lying and this is actually 25p.

Aaaaaghhhhh!!!!

I thought you knew the difference between native acquired interlaced and distributed interlaced. Movies are shot on film at 24p (or 25p if shot for a 50Hz market directly). 50Hz DVD releases will usually speed 24p up to 25p and use 2:2 pulldown (i.e. show one frame for 2 fields, then the next frame for 2 fields).

However 50Hz MPEG2 DVDs are often (always?) mastered in 50i. If you master a 25p source in 50i there will obviously be no motion between the two fields in the frame (effectively it is psf) - so you don't actually have to do anything to deinterlace other than present both fields weaved together (this is why you WEAVE 25p content received in a 50i wrapper). Effectively you create a 576 line image by using one 288 field for the odd lines and the next 288 line field for the even lines etc. and show it twice (once per field)

My point is about native interlaced material. This won't be a movie or high-end TV drama (in fact even many soaps now shoot 25p rather than 50i) - it will be entertainment, sport or news.

These sources will have motion between the two fields in a frame (as they are captured 1/50th second apart) - so you need to recreate the missing fields (you can't use the other field as you can for a WEAVE). Bob does this by duplicating (sometimes with a bit of filtering) the same field giving you lower vertical resolution, but 50 images per second with no combing (but jaggies instead). Then you get more and more sophisticated algorithms

However - the major difference between 25p and 50i native content is that 50i native content, when correctly deinterlaced, will have a very different look - it will be fluid 50Hz rather than slightly juddery 25Hz.

Black Hawk Down is a movie. It will have native 25Hz judder (due to only capturing 25 images a second). 50i native content captures 50 pictures a second, so when correctly deinterlaced should have 50Hz motion (which will look a lot more fluid than 25Hz)

ffmpeg won't know that the source is progressive without doing some analysis of the actual image content. The only real way of telling if a source is acquired interlaced or progressive is to watch it.

Obviously if you have Natural Motion, MotionFlow etc. enabled on your TV and it is converting 25p to look like 50i (i.e. the soap opera effect) you can't see the difference as you aren't watching the real video, but a mangled version of it. But if you have all these processes disabled - you will clearly see 25p from 50i content (or should be able to if you have a half-way critical eye)