Field order problem

[dukey]

I have this video and it appears 100% interlaced. However in tmpgenc, if i select top field first, then in the inverse telecine option i select the B frames i get 100% progressive picture. If i select bottom field first i can only seem to get interlaced material.

How do i do this in avisynth ?
I've tried messing with the swapfield options and other things but have had no luck

My script is this atm

DGDecode_MPEG2Source("video.d2v")
BicubicResize(688,352)

Edit:
I figured out what is wrong I think. One field in each frame is in the wrong frame !

So
field(a,b) + field(a,b)

instead it's something like

field(b,a) + field(b,a)

where field b should be shifted into the previous frame

How can i do this with avisynth ?

[ChiDragon]

It's not a field order problem but a field "phase" problem. If you're sure that the shifting is constant then "SeparateFields().Trim(1,0).Weave()" or "DoubleWeave().SelectOdd()" will do the trick. For automatic field matching use Telecide or TFM without any decimation filters.

[IanB]

DoubleWeave().SelectOdd() is prefered as it is faster. ;)

Internally there is DoubleWeaveFields() which does the mundane and DoubleWeaveFrames() which takes some shortcuts to be as fast as possible.

[dukey]

DoubleWeave().SelectOdd()

that did the trick :)
Yes the phase shift thing was consistent to the very end of the video.

Many thanks :)