I can't say it's impossible, but I know of no way to loop a video on an iPad.
As to linking up a series of them, unless you want to try to write your own app (and even then it's iffy), that's not going to be possible.
I think you'll be best off with something like a Mac mini, a touchscreen, and a presentation/kiosk application. For driving multiple displays you may be forced to a Mac Pro if you want those displays synchronized.
I had the same problem and followed FrancisStie's suggestion. It worked without compressing the video. I also tried "vloop", and was disappointed by the video quality. It is surprising that apple does not have a ready solution, and we are left to hack these back door methods. It would make sense for the video player to have a repeat option.
1. In iphoto, import the video and create a photo album for it.
2. Upload the album to ipad through itunes
3. On ipad, in settings, make sure that slide shows are set to repeat.
3. On ipad, in photos go into the Albums screen, select your movie.
4. Choose slideshow , click Start Slideshow
To loop videos get LoopyLoopy, it's free. For a while I've been using Video Loop Presenter and had problems getting both an iPad 1 and iPad 2 to see the videos. With Video Loop Presenter you need to use a utility called iPhone Explorer to copy videos to the camera roll. If it's not in the camera roll it won't be recognized. It worked ok for 1 video, then weird things would happen. It wouldn't recognize all 6 videos I have, just selected ones. Truly flaky behavior. With LoopyLoopy the interface is set up through iTunes to implicitly recognize videos you want it to play. To do this you have to use the File Sharing feature in iTunes. Here are the directions:
For all you who have been looking for a solution for the problem above, here it is :
The Kiosk Pro app allows you to run any html-scrip locally stored on the ipad!
Which is great! Because not only does it allow for an infinite amount of possibilities next to the video-looping, it also keeps on working with one click after a reboot!
The learning curve of usage is quite simple for the problem above, since they provide extensive information on the website and have great customer service.
I am very very happy I found this app, and I really hope this post saves a lot of people the headaches I've suffered in the course of finding the solution.
You can't do this because Steve Jobs knows better! Even if you think you want it, you don't because Steve Jobs has already thought of that for you. Wanting to loop a video is just crazy insane. In today's world you actually expect that some one in charge of your IOS will supply a simple button that lets you loop a video. Next you,ll be wanting multiuser login ability so you can share your ipad with your family with privacy ensured. Remember inflatable Steve said no to small iPads and we all know that ipad mini was a complete failure and Steve was right again! LOL.
...oh wait, that's Android that does all that already!