Originally Posted by David Jimerson (Post 1655185)

The frame rate and p or i are not the same thing. Progressive means full-frame pictures are taken. Interlaced means half-frame pictures are taken, the half being every other line of vertical resolution (line 1, line 3, line 5, etc., then the next picture would be the even-numbered lines).

A few points:

60i is often called "30i" or "29.97i," because the time code is based on 29.97 frames per second, but it's inaccurate, misleading, and confusing. It's a throwback which is no longer necessary.

60i is more properly called "59.94i." This is because there are actually 60 (59.94) pictures taken per second, not 30. Each interlaced field is a separate picture. They say two fields put together make a "frame," but anyone who's worked with video knows why that isn't true -- you'll see the comb artifacts made by mashing together two pictures taken at different times.

This matters to the motion, too, because a moving object is in twice as many positions per second as it would be in true 30 fps. True 30 fps would be 30 pictures per second, meaning there's twice as wide a gap between the positions of moving objects from picture to picture. Obviously, less of a gap means smoother motion, so 60i motion is twice as fluid as 30p.

So, you can see why 60i and 60p would have the same motion -- it's the same number of positions per second for any moving object. 60p being progressive, the resolution of a 60p frame is twice that of any 60i field, but the motion characteristics are exactly the same.

There really is no such thing as 30i or 29.97i -- no format shoots or displays 30 interlaced fields per second. But, you'll still see that nomenclature in legacy equipment and software with a history going back more than a decade. Would be nice if it would go away, because it's confusing.