Footage is already progressive. why does any unit need to deinterlace?

because SD DVD's are always interlaced.

I don't believe this statement is correct.

Sean see this link it may help you out.
http://www.kenstone.net/fcp_homepage/hdv_to_sd_dvd.html

^^^the only thing that little tutorial demonstrates is how to encode progressive HD video to a standard def DVD. The DVD will still be authored as 480/60i, just as every other SD DVD has been done since the inception of the format. If it were possible to author a truly progressive SD DVD, it would not display on any interlaced CRT because, to my knowledge, no SD DVD player can interlace progressive video on the fly - progressive DVD players are designed to do just the opposite - de-interlace an interlaced DVD.

Ever make the mistake of trying to output progressive to an interlaced CRT lacking a de-interlacing chipset, LOL? That's exactly what would happen with a progressive SD DVD playing back over component vid hooked up to any interlaced CRT (lacking a de-interlacer ...sorry, lacking an active INTERLACER... - just about every single SD CRT television in existence).

The SD DVD format was created specifically for interfacing with interlaced televisions - because that's essentially all we had 10-15 years ago. Now, we all have progressive sets and that's why I say that the BDA really blew it when it failed to include native 1080/30P in the format.

Thanks for the link!

Aaron, why are there still things like interlaced HD formats, when, as you mentioned on another thread, most modern HD sets are progressive?

IMO, because the people controlling the advancement of technology are too firmly rooted in the past, short-sighted, or just dumb, LOL. And it's not like the tech isn't there. Didn't NHK or some other Japanese broadcaster demonstrate 1080/60P broadcast television at 2007's CES? Also, Harris already has 1080/60P equipment available. And the video processing chipset manufacturers are already developing 1440P products, LOL.

Things are not going to stand still in this arena. Unfortunately, the ATSC committee prematurely IMO decided to stick with MPEG-2 instead of a more advanced codec like AVCHD/H.264/MPEG-4/VC-1 - pick your flavor - although, in their defense, I don't think any of those existed, what 10 years ago when the official ATSC spec was put to paper <--please verify the exact timeframe, I'm just best guessing here without looking it up.

So now you're trying to cram multiple Gb/s of data into a 19Mb/s broadcast television bandwidth allocation. Something's got to give, LOL, and it clearly IS.

Thought I would edit this to include a nifty little background read I just discovered that might shed some more insight on this topic. It's somewhat dated, but very, very relevant IMO. This guy certainly has quite the credentials so I have no reason to doubt him. So, a fourth reason would evidently be ulterior motives.

http://www.vxm.com/Progvsinter.html

Wow, I've got to bump this up after reading the info in that link a second time. The above-referenced is LOADED with very interesting tidbits of knowledge and experience that are very relevant to many discussions on this site. HIGHLY RECOMMENDED READ!