'Schooner' - Depending on how much footage you wish to convert, I have a solution which I have used. It's labour-intensive, though, and I wouldn't recommend it for gigabytes of footage at-a-time. I had to devise this solution when I made a video of an overseas holiday, was stopped by the weather from achieving all that I set out to do, and had to mix Sony DV footage from a previous trip with MOV footage from my current JVC camcorder. Additionally, my work was in 16:9. The problem was that some of my vacation footage was shot in 4X3 format, before I became aware of the fact, plus, I also wanted to incorporate 'P-i-P' stuff shot in 1991, which was of historical interest but in 4X3 format.
In short, I used the graphics manipulation program GIMP for aspect-ratio conversion. This calls for short items of video to be processed at-a-time. The full 'GIMP' is needed, including the animation-module which splits sequences up into individual frames, then re-assembles them again after the changes have been effected. Sounds like a hell of a lot of work, and is, but it allows the 'impossible' to be achieved. Also with a bit of practice, you become better organised, and much faster at-it. Needless to say, you edit down the material first, so as to not have to convert footage which later won't be used.
I took the trouble of writing a 'tutorial' on the subject, since I belong to an active video-club. I failed to interest many in it, although it explains with great care and clarity what is needed, blow-by-blow as you do the button-pressing.
I have been involved, also, in an on-going documentary wildlife series. The first few excursions were filmed in 4X3 format, before I realised that 16:9 was plainly needed. GIMP was used, again, to crop the clips I wanted to use to 16:9, and then to reconstitute it all.
The full procedures are far too long-winded to go into here, but if you are still interested and care to contact me, I would be delighted to send you the full text of the article. My email is <artsmith@clear.net.nz>
Ian Smith, Dunedin, N.Z.