Mencoder: 25fps interlaced to progressive?

[nexx]

I've recorded some content in 576i and 1080i via my HDTV card, and I'm after the best way to turn these into progressive movies when encoding to XviD.

I've done some research and tests and come to the following conclusions:

Since I plan on scaling the video down a lot (1920x1080 > 720x404), I should just discard one field (-field=0). But this results in jerkiness as half the fields are missing.

The alternative seems to be to display every field as a frame (-tfields=1 -fps 50 -ofps 50) - I end up with fluid motion but at twice the frame rate, requiring a much larger file for decent quality.

So it seems a compromise between fluidity and size, is there no way to get a fluid 25fps video out of this?

Any help appreciated