The effect of Avisynth "selectevery"

[davexnet]

Hello all,
I've been playing around with some old, SD music videos I had on my PC, a few of which are
interlaced mpg. As an exercise, I wanted to try the PAL to NTSC conversion to see how it looked.
This technique preserves the interlacing, thus the temporal fluidity.
Here's the script:

MPEG2Source("F:\interlaced_vid1.d2v")
yadif(mode=1)
ChangeFPS(60000, 1001) # convert from 50 to 59.94
Separatefields().SelectEvery(4,0,3)
lanczosresize(720,240) # resize for NTSC
Weave()

On this page, http://avisynth.nl/index.php/FPS
it says of SelectEvery: "Use SelectEvery(4,1,2) for odd field first."

Here's my question. Is there any practical difference whether 4,1,2 or 4,0,3 is used,
as long as the field order is taken into account when the script is encoded?

I know it's a bit of an esoteric issue, but appreciate any insight.

[manono]

Is there any practical difference whether 4,1,2 or 4,0,3 is used,
as long as the field order is taken into account when the script is encoded?

Yes, you want to use the uninterpolated fields.

Usually bobbers keep one field unchanged (not QTGMC though) and interpolate the other. Use 4,0,3.

I think that's right. Someone will come along and correct me soon if I'm wrong about anything I've said.

[jagabo]

Nevermind

[davexnet]

Thanks for the info. I thought *all* the output from the Bob is interpolated equally, since it's turning
each field into complete frames. On top of that the ChangeFPS adds duplicates, to further complicate things.

I haven't seen any difference in terms of the quality with either 4,0,3 or 4,1,2 but it could be that the
video I'm looking at is just too cruddy to notice the difference. Certainly the field order is flipped.