Server having trouble playing back certain .mv4 or .mp4 files

Question

Hello folks,
I'm really stumped about why certain .mv4 or .mp4 files do not playback well off of the server for my website www.listenup.org -- a large archive of youth media video.
At first, I had a few files that weren't working because there were non-alphanumeric characters in the names. But even after renaming them on the server and in the database, they still sit on the site longer before opening.
I can't send live to the site the videos that really aren't working at all (which I have mostly solved anyway -- users tacking on the wrong extensions or having non-alphanumerics in name), but here are the real mysteries -- the ones that load for a considerable time longer than the others before displaying the download progress bar quicktime playback tool.
All of these videos do work. And by leaving one or another sitting there for about 30sec - 1 min it should appear (and they are pretty good anyhow). At the end of the downloading process, you can right click and use "Save as Source" (these are all on Creative Commons licenses of various sorts).
Here are a few problem videos:
http://www.listenup.org/screeningroom/view.php?media=ae9e78f2d591206ab070b699478 8b8c5
http://www.listenup.org/screeningroom/view.php?media=cbd34b179c2f3e2a758a3d840ef e7d2c
And here are several collections where everything seems to be fine, even with videos with rather hefty datarates, videos that are iPod video 640x426 or 320x240, you name it:
http://www.listenup.org/screeningroom/cat.php?view=7c599d3bc98f45d2803c3fd5ec737 01b
http://www.listenup.org/screeningroom/cat.php?view=d9c8ba16e3295518c7f7cc6a4b75c ca9
If there is some processing action that I could do to these to make sure that they load immediately when a visitor clicks on them I will be happy. (Even if the progress is very slow! that's a member's prerogative whether they want to compress video with a larger web visitor community in mind!) I'd rather not rerun these through iTunes or similar to "Convert to iPod" because a) I don't know what I'm doing that is making the files better, and b) it almost always seems to make the files bigger with no perceptible gain in quality. If that is what I should do, though, I can certainly do that and replace these on the server.
Thanks so much for your QT guru-ness. It is times like these that I wish I knew more about quicktime from a developers point of view!
Thanks,
Matt
G4 Al-Book (1.25 GHz) Mac OS X (10.4.9) laptop

Answer 1

This is very helpful! How do I create .m4v or .mp4 vidoes that "Fast start"? Just changing the extension doesn't work -- and exporting takes time. I'd love another fast solution like this for opening and "Save As" -- that results in the MPEG-4 extensions that my users are expecting. (Yes, QT is a container format, and yes this .mov has the same media H.264 media streams, but we'd like folks to be able to drag these into itunes or similar and get them quickly on iPods.)
Thanks!
matt