Wrong field order - fix w/o re-encode - invalid mpeg4 file?

[KuroNeko]

I have an avi file, MP3 CBR audio, DIVX3 Fast Motion, 29.971 frames /sec (and Gspot says also 29.971 fiels/sec - does this mean it is not interlaced?).

It has a lot of combing artefacts, even on an interlaced display. I am assuming it is encoded interlaced in the wrong field order, or progressive, but again created with the wrong field order.

MPEGmodifier can fix this but reports it is an invalid MPEG4 video (startcode not found at beginning of frame)

Any ideas what's wrong with this file and can it be fixed (preferably without re-encoding)?

Thanks for any help!

Neko

[KuroNeko]

After a lot of experimentation I think the person who encoded it made a simple merge/weave-deinterlacing to progressive, then encoded.

How do I remove this, is there a way to re-interlace properly and then do a good deinterlacing? Re-encoding seems to be the only way to fix this.

Thx
Neko