We're awake and able to respond now (but weren't when you first wrote at 6:25 am !)...

1) Apply interlace filter was renamed, for clarity, to "Reduce interlace flicker" in Vegas 3.0a. The online help description covers it pretty well:

"This switch can be useful in cases where the source material didn't originate as video and contains extremely high spatial or temporal frequencies.

When you watch the rendered (interlaced) output on video of this sort of media, you may see flickering or crawling edges if this switch is not applied."

2) Video resample switch (again from Vegas online help):

"Resampling allows Vegas to interpolate frames in an event when the frame rate of a media file is lower than the project’s frame rate. With resampling, the intervening frames are interpolated from the source frames, much like a crossfade effect between the original frames.

This may solve some interlacing problems and other jittery output problems that result when you're using source material that did not originate as video (generated graphics, still-image sequences, or video rendered by some 3D applications)."

We considered making this turn on automatically when timestretching video, but there are some cases when this would not help and would just add to the render time. In the future, we may expose a pref that turns this on automatically when timestretching.

I believe the original poster wanted to know what the Interlace filter does. you haven't answered the question by quoting the help file. We've read the 'explanation' offered there.

I would also like to know what this filter does, since I have some material that exhibits crawling/shimmering, but is actually NOT interlaced.

Digital photos with lots of little details seem to have this problem when zooming/panning on them at just the right rate. I'm rendering to DV progressive and watching this on my monitor. I'm wondering what the 'Reduce Interlace Flicker' filter does, so that I can figure out if similar techniques can solve my problem.

Another problem with the help file, is that it wasn't updated all the way from VV2.

EXAMPLE: There is a new Median filter in VV3 with more capabilities. but the VV3 help file only has a section for the VV2 median filter. none of the new options are addressed, and I have no idea why they were added nor how to utilize them properly. they were obviously added for a reason, it would be nice to know what the reasons were. it is somewhat frustrating that all the median filters I applied to VV2 projects are now broken since they get zero'd out when opening the projects in VV3 due to the new Median filter. I'd be less frustrated if the help file wasn't completely oblivious to the new filter settings.

The interlace filter applies a small amount of vertical-only filtering so that high-frequency elements don't twitter as they move. The best example of when you'd want to use it is on a credit roll with serifed fonts or characters with thin horizontal bars. Depending on the roll speed, these elements can "beat" with the interlacing rate and cause twitter on the display. Imagine a roll speed *just faster* than one scanline per field time. For many fields in a row, the element lines up with a field line, and is displayed. Then (because the roll is slightly faster), it lines up with the "other" field for each rendered field, and therefore disappears for a while. When you view this sequence, the elements fades in and out as it scrolls up. Depending on the roll speed, this beating might be very fast or take many seconds (as in the nature of beating, it's a modulus type of thing). The interlace filter, by applying a small vertical blur, bleeds half the energy from the element into adjacent scanlines, and the artifact is removed. It is only needed for "high frequency" sources such as small text or imported images. Video shot on a camera has already been filtered by the camera.
///d@

It's also critical when importing stills that contain small vertical or diagonal lines, and the still is panned or cropped.
Further, it helps when someone has created bad audio that leaks into the video bandwidth and it causes the video to twitter. (yes, bad audio can screw up video. And bad video can screw with audio, but it's less common.)

Well, THANK YOU ALL !!!
- SonicEPM, my fault, I apologize ! I forgot that the world is round :-) 6:25AM "there", 11:25AM "here"... Now, 8:10AM "here", 3:10AM "there" ... sleep well, my friend.
- SonicEPM, I am aware of the help text (by the way, it is exactly the same as the text in the manual), but, as I said in another post, reading the help is a dog, because Vegas insist on reloading all the job (90 seconds to me) each time that another application is used (including WinHelp). Really annoying, maybe an improvement for a later fix (having reload as an option, load as a default).
- and my original claim was about uncomprehensible things like "extremely high spatial or temporal frequencies" (what ?). I *wrote* that I had read the help and manual ...
- "reduce interlace flicker" is more clear to me that "interlace filter". Go figure !!!
- cheesehole remarks are right, and I second the opinion. Zoom + Pan on stills is bad news. Resampling does quite better it a little, but I think that the filter applies blur to the scene (try zooming on an image of a text page). Anyway, I don't know if progressive scan helps much, considering SonicEPM explanation (later). You should try lower field first.
- SonicEPM. Oh Yeah !!! Your second approach to the theme was much more like it. Now it makes much more sense to me. Thanks for that, that's what I was seeking in the first place.
- SPOT is right (spot on, if you pardon the pun). And now, I am surprised, I was not aware that bad audio can leak in video bandwidth !!! It's quite an interesting theme for a topic of its own. Would you care posting your wisdom about the subject in a different posting, so that we can all add our grain of salt (or lots of questions ?) Appreciate.
Bless you all.