Playing so called "NTSC" mpegs, framerate

[j7n]

When I play back MPEG files from 'NTSC' standard DVDs, all players (ffdshow, BSPlayer) say I have a framerate of 29.970 f/s. However, 'film' video is output at its true 24 f/s. Which component of the system is responsible for restoring the full frames? I thought that it was the decoder, but why would it say 29.970 then?

[Leak]

When I play back MPEG files from 'NTSC' standard DVDs, all players (ffdshow, BSPlayer) say I have a framerate of 29.970 f/s. However, 'film' video is output at its true 24 f/s. Which component of the system is responsible for restoring the full frames? I thought that it was the decoder, but why would it say 29.970 then?
That's because the video would really be 29.97 FPS if the renderer (or some filter in-between) would be honoring the field order flags set on the individual frames to apply a 3:2 pulldown before presenting the frames.

Ignoring them is what most players do to get progressive frames, but sadly that only works if the flags were set correctly when the DVD was made...

(Since that goes wrong often enough I've been whacking at ffdshow (http://sourceforge.net/tracker/index.php?func=detail&aid=1676882&group_id=173941&atid=867362) a bit lately...)

[j7n]

What would be the visual artifacts when playing a DVD with incorrectly set flags? Extra frames, out of sync, combing?

[foxyshadis]

Jerky video, mainly. In normal pulldown, you have:
1A, 1B, 1A, 2B, 2A, 2B, 3A, 3B...
In bad pulldown, or pulldown on pure interlaced, you might have:
1A, 1B, 2A, 1B, 2A, 2B... or
1A, 1B, 2A, 1B, 3A, 3B...
That backwards jump makes a jarring viewing experience. (Actually, I don't think that first bad example is legal, come to think of it.)

[j7n]

Is it possible that when playing NTSC film video frames don't come out precisely with 41.6 ms intervals?

To a naked eye american releases seem a lot more jerky than european, more than could be attributed to the frame rate difference.