Oh wait I just realized something... It's for ipod video use I think
I was thinking something similar. I think you can play youtube on some cellphones (or maybe just iphone??), and I think that's what the .3gp version is for. If someone managed to work out what url iphone was accessing they'd have seen the extra bit in the url and experimented with other numbers. I'm just clutching at straws here.
I saved the url's of the files that wouldn't download and I tried them again later (when maybe things were less busy?) and they worked.
I noticed the info in the video...
Audio: AAC 44100Hz stereo 110Kbps [(C) 2007 Google Inc. v06.24.2007.]
Video: MPEG4 Video (AVC) 400x304 [(C) 2007 Google Inc. v06.24.2007.]
Google video. Maybe they first started making mp4's when Google bought youtube. I know that Google Video (Google video now lists youtube stuff, I'm talking about original Google Video) allows you to download in avi or pmp so maybe it's connected with that somehow. I have noticed that some files I tried to download (uploaded in 2006) wouldn't download. Also one uploaded last week won't download. Maybe there's a backlog of encoding to do or
maybe they stopped doing it. I've saved the url and I'l try it again later.
^ then its time to experiment with more parameters to see if the original file is also downloadable?
I was thinking that too, maybe there's a tag you can add to get the original file, no matter what filetype it is?
One thing I noticed about aspect ratio was that sometimes I download a flv and it's really stretched and tall, but when I downloaded the mp4 of one like this it looks normal. A shame I can't find a rare Ayu video that was stretched, it's probably gone now. Another advantage is I can play mp4 with media player classic and easily change the aspect ratio and audio sync with a few keypresses and play them full screen. With flv I couldn't play them very large, when I play flv in a big window it really thrashes my cpu.
Weird, the embedded one that says "it doesn't" works for me! (EDIT:But it plasy as a 320x240 flv)
EDIT: I tried to embed one that doesn't have an mp4 (repeated attempts and it never plays), and it played but it was igonring the tag for me and just played the normal flv.
EDIT2:I tried one that I knew was there and got the message "We're sorry, this video is no longer available."