[StainlessS]

Can someone confirm,
When compressed by dropping fields, they are dropped in top/bottom or bottom/top pairs (even if not from same original frame pair, I guess they MUST be).

So there are these (original pre drop) possibilities ('.' being missing field)

 t1 | t2 | .  | t4
-------------------    TYPE A
 b1 | b2 | .  | b4


 t1 | t2 | .  | t4
-------------------    TYPE B
 b1 | .  | b3 | b4


 t1 | .  | t3 | t4
-------------------    TYPE C
 b1 | b2 | .  | b4

And TYPE B would imply TFF, and TYPE C BFF.
And if TFF, then only types A or B could be present, if BFF then types A or C only. [possibly two types mixed if edited after time compression, or compression in pieces]
All three types should never [legally] occur in a stream. [Otherwise as in DGIndex, "Illegal Field Order Transition"]

EDIT: For Progressive Frames dropped, could try Duplicity/DropDeadGorgeous combo.

Duplicity/DropDeadGorgeous:- What they can do.
Duplicity: Creates dupe DBase for use by DropDeadGorgeous. You can use ChangeFPS to insert duplicate frames to same framerate as desired output (use dupes as markers when creating DBase).
DropDeadGorgeous: Searches for duplicate, then on finding dupe, scans to at most "ScanAhead" frames prior to dupe looking for frame with biggest difference from its predecessor. [Dupe or SceneChange curtails big diff scan distance]
Interpolate at biggest diff frame and move along one, the frames between big diff (inclusive) to the frame before the dupe,
this sqeezes out the dupe and inserts an interpolated frame where biggest diff is found.
Advantage: All non dupe original frames are kept verbatim in output.

Locate Dupe, scan prior to dupe to find biggest diff, interpolate at big diff and relocate frames following bigdiff along to squeeze out the dupe.

12345678      IN: Where 7 is Dupe, and diff 2->3 is Big (B)
  |   |
  B   D

12I34568      OUT: Interpolates 2->3 (I), relocates (R) following frames along one place to squeeze out the dupe (dupe frame 7 gone).
  |||||
  IRRRR

Where multiple consecutive dupes (M) found, then will interpolate M frames at B, and relocate frames B to first dupe - 1, to squeeze out the dupes.

12345678      IN: Multiple consecutive dupes=2(M), Where 6 & 7 are Dupe, and diff 2->3 is Big (B)
  |  ||
  B  DD

12II3458      OUT: Interpolates 2(M) frames(I, 2->3 as interp source), relocates (R) following frames along 2(M) places to squeeze out the dupes (dupe frames 6 & 7 gone).
  |||||
  IIRRR