Preview in iTunes takes 5 min to load

Question

Our iTunes U site hasn't gone public yet, but we're uploading a lot of content to test things out. I've noticed with some videos (with what seems to be the same compression settings) if you click on the preview icon within iTunes U, it literally takes 3-5 minutes for the video to appear, during which time there's a "loading" message. The video eventually shows up, and if you hit "Get Movie", there's no problem downloading it and watching it on your own machine.
Many of the videos that don't work have the following settings (from Quicktime movie inspector):
H.264 Decoder, 320 x 240, Millions
AAC, Stereo (L R), 32.000 kHz
There's some files with these same properties that do work, though, and if you re-compress these using the iPod setting in Quicktime, you don't get the delay.
Strangely enough, I've never had any problems with videos compressed with:
Sorenson Video 3 Decompressor, 320 x 240, Millions+
MPEG Layer 3, Mono, 48.000 kHz
But, of course, these can't be transferred to your iPod.
The folks who made these videos claim that their process is consistent, and there should be no difference with the files. For what it's worth, they use Squeeze to do their compression.
I'm really stumped on this, and it's been throwing a wrench in our progress on the site (which needs to launch in about a month.) Any help would be wonderful.
Thanks,
Quinn

Answer 1

Actually, after some feedback from Apple and some testing it does look like iTunes U and iTunes does support progresive download fast start. With QuickTime 2.1, Apple introduced the Fast Start movie, which is a movie with the header at the start of the file. It works because the movie atom is stored at the beginning of the file. So, QuickTime knows how to interpret the movie sample data even before it arrives, and because the movie data is intelligently interleaved with respect to display time.
When the bandwidth of a connection meets or exceeds the data rate of the movie, a well-formed QuickTime movie file can play as it downloads. This kind of progressive download, or Fast Start movie, provides the same user experience as real-time streaming.
Originally, a special tool was needed to process the move for fast start. However, making fast start movies is now the default move of QuickTime. However, if you do any editing in QuickTime Player, even simple things like changing annotations, the header gets moved to the back of the file again, and fast start no longer works. When this happens, you ned to re-flatten the move, either by doing a Save As of the file from QuickTime Player.
There is a freeware utility that can be used to flatten movie (mov and mp4):
http://www.qtbridge.com/lillipot/lillipot.html
We use have used Sorenson Squeeze, which appears to not have GUI option to enable/disable progressive download fast start.
Most other compression tools let you set the progressive download, fast start option.
So, for example, on our iTunes U site we have progressive download fast start video's that play directly from iTunes U without issues.
http://deimos.apple.com/WebObjects/Core.woa/Browse/utah.edu.1413595482.014207570 81.1419303557?i=1534614695
But, we also have video that were encoded with Sorenson Squeeze or other tools without the fast start option. Thye do not play properly from iTunes U.
In regards to previewing & downloading media is possible, if the media is progresive download fast start, but the interface could be modified to make it more obvious.
IMHO, iTunes should better optimized to handle playback of non-fast start media, no raindbow beachball and hog resources for iTunes will trying to load media.