A lot of older DVD video is available only in interlaced format. Back in the day, the only screen format was 4:3 SD (NTSC and PAL) and all TV sets used interlacing to avoid screen flicker. The old tube and early transistor circuitry bandwidth could barely keep up those framerates.
(During the development of the first color TVs, the development engineers actually tested to see how bad of a picture the public would tolerate in order to determine what they could ‘get away with’ technically to keep the cost of producing a saleable product down.)
Widescreen movies were letterboxed and the number of lines and pixels in those images were miniscule by today’s standards. (I think back and wonder how we actually watched that stuff.)
Anyway, to make a long story short before the advent of HD TV, all DVD video was interlaced and used lossy compression. The feat of getting enough useful information from those old, noisy, frames, interpreting it, adding detail and rescaling it to HD is actually a miracle. We’d never be able to do it without the aid of AI.
Bottom line: There are many years of old pre-HD video out there, and the majority of it is interlaced. And, unless you want an unacceptable 2x “progressive” framerate, you need to merge those 2x frames down to 1x. Otherwise, the conversion output may be progressive, but it really isn’t
That is why we have the Interlaced Progressive section of enhancements. It is also why we have seen the implementation of screen interpolation, which was originally adopted for slow motion. now being used for converting the 2x pseudo-progressive down to fully progressive, potentially at its original frame rate. of 30 or 25 FPS depending on whether it is/was PAL or NTSC.
