interlacing in progressive DVD image

[ecc]

I am reviewing a DVD and I am told by the encoder that it was encoded at 23.98 with the Sonic encoder but while the image is progressive, I notice occasional combing in bright areas of certain frames or one frame every once in a while that is interlaced. The NTSC disc runs the same length as the PAL disc but there is no noticeable ghosting.

DGIndex says that the framerate is 29.97 and 30fps and is progressive while GSpot says it is 29.970 FRAMES per second and 23.976 PICTURES per second. [s:89944dda0f]Shouldn't that be the other way around with a 23.976 film transfer flagged for 3:2 pulldown?
[/s:89944dda0f] EDIT: checked a progressive MGM disc and I was wrong as GSpot also says 23.976 for pics and 29.970 for frames.

Might this be an example of the Alchemist method of standards conversion which one site says "which compensates for the difference in frame rates by dissolving each frame into the next" while a forum post says it "uses motion vector technology" to turn 25fps to 30 fps?

Could the master have been converted to NTSC using this method and then encoded as progressive 23.98 (I'm not sure if he actually encoded it at 23.98 or was just rounding off 23.976)? Would it be a mistake to encoded it at the rate or is it supposed to look like this when this method of transfer is done? Reportedly one or two Criterion transfers also use this.

[jagabo]

GSpot assumes 23.976 pictures per second when it encounters a progressive source with pulldown flags. It doesn't really examine the pulldown pattern to determine the real progressive frame rate (although 23.976 is usuallly correct).

Try opening your file with VirtualDubMod. It ignores pulldown flags and shows you each frame as if it was progressive. If you see comb artifacts there the video was simply converted/encoded incorrectly. VirtualDubMod may also report the wrong frame rate because of the ignored pulldown flags.