Unwanted Pillarboxing in 4:3 .mov file created from 4:3 .avi file

Question

I have been having problems prepping 4:3 .AVI and .DV files for use in Final Cut Express 4. Final Cut Pro is happiest using DV/DVCPRO .mov files, so I have been using Quicktime Pro to do the conversion. The problem is that QTP adds pillarboxing into the video converted from the AVIs: approximately 7 pixels wide black bars on the left and right edges of the video frame. The black bars are NOT visible in the original AVI when it is viewed in QTP, no matter what presentation aperture I select in the QTP Movie Properties window. The black bars are visible in the converted file (DV/DVCPRO .mov) created from the AVI when I view it in QTP, in any presentation aperture but "Clean".
If I drop the .mov files into either iMovie 6 or FCE 4, the bars are visible. If I drop the original AVI into FCE 4 or iMovie 6, there are no black bars. Interestingly, when I drag the .DV files iMovie 6 creates from the AVI out of iMovie and then play it in QTP, it does not have black bars (using any presentation aperture). I can drop this .DV into FCE 4 and see no black bars. If I use QTP to convert the original file AVI to the same .DV format as created by iMovie, I get black bars!
Quicktime and Quicktime Pro Version is 7.3.1.
The initial AVI format is: Apple OpenDML JPEG, 640x480 (its 4:3 video with square pixels), 30fps, progressive, millions of colors, Sound: 8-bit unsigned integer mono, 11.024kHz.
The output QT .mov file format I am using is: DV/DVCPRO, 4:3, 29.97fps, progressive, Sound : 16-bit 48 kHz, Stereo.
I have tried various output sizes: 640x480, 720x480 4:3, 720x486 4:3, "Compressor Native" (which should be the same as 720x480 4:3), and "Current" (which says its using 640x480). All the variations generate black bars. Out of desperation, I even tried exporting interlaced, rather than progressive, and of course that had no effect. I get exactly the same behavior in MPEG Streamclip, so it seems possible there may be something deep in Quicktime itself that is responsible, not just QTP.
QTP seems to want a square pixel 640x480 4:3 video to be 654x480 to get it to 4:3. That's a 4.0875:3 aspect ratio. I have been searching high and low on the net for definitive info on this. I have seen references to Apple adding the notion of "Aperture" to the QTP interface and to using 4.09:3 aspect ratios, and Apple saying there is no real defined standard. Whatever that means.
Does anyone know what is going on here? Can anyone point me at a web page that explains Apple's ideas about aspect ratios? Is there a checkbox in QTP that I have overlooked that would give me control over this behavior?
As described above, iMovie 6 certainly seems to know how to use the Quicktime engine in such a way not to introduce the black bars. It just doesn't create the format I need!

Answer 1

I think I just found the solution to my problem. When I open the original AVI file and look in the Movie Properties Presentation tab, the "Conform to Aperture" option is checked, and set to "Clean". If I uncheck it and THEN export the movie to either a .mov or .dv file, Quicktime Pro doesn't add black bars on the left and right in the output movie, and the resulting file works great in FCE4 and iMovie 6!
I thought the conform to aperture was just a viewer mode, and didn't realize it could modify the content of the video during conversions. Still, I would still be interested if anyone could provide links to web pages that explain this better. Thanks.