Video is not working correctly for me - help?

I'm running Omeka 1.5 on a shared host. I'm trying to get some video working. The 25 minute long version was a bust. I've been experimenting with breaking it into shorter segments, increasing max_execution_time and other variables, but seemingly to no avail.
I've got one short clip as an .avi file - which sort of works. I've also got a short clip as a .mp4, which has excellent sound, but doesn't show any video. (When I view the file locally everything is fine.) (I really don't like the look of the player for the avi.)
The mp4 starts playing automatically when I access the page. This is not ideal behavior.

What's the easiest file format to use?
What's the max file size that I can work with (I realize this depends somewhat on php.ini settings, but what should I be aware of in setting maximums)?
Can I mix file formats? (When I just had the avi up, it worked okay - adding the mp4 caused the avi to work poorly.)
(See to see what I'm talking about - the avi is the top video)

It looks like you're using the HTML5 Media plugin, which is what's getting you the nicer-looking player for your MP4 file.

Video support, even with HTML5 Media, is a little tricky still on the Web, and your MP4 file uses a video format that's pretty well supported on desktops, but not well supported by browsers (MPEG-4 Part 2). The audio in that clip is AAC, which is well-supported.

If you instead use an H.264 video, the HTML5 Media player should work on pretty much any modern browser. The confusing part is that H.264 video for the web usually still comes in a .mp4 file.

For the mp4 file, the bottom line is that it looks like you're using a video codec that browsers don't support.

As for the AVI file, it's just being rendered with the system's default plugin, something like Windows Media Player or Flip4Mac. Omeka can't do much about the way AVIs look or perform.

For best results with the HTML5 Media plugin, you should try to use H.264 video and AAC audio in an MP4 file. This should work on all browsers, Android, iOS, and Windows Phone.

As a bonus, H.264 video results in smaller video files for the same quality than the codecs you're currently using.

John, thank you for the helpful response! I'll redo the clips as H.264 MP4 files.

I now have another problem/question:
This morning, around 4 am, Omeka started moving a "huge mp4 file" to the server's tmp folder. They shut down my account due to what they perceived to be a script or cron job creating mp4 files like crazy. From what they've told me (I'm afraid I may know more about this than the tech guy I talked to does), it sounds like it was really only the one file (I think from when I'd uploaded the whole video at once before I realized that was a bad idea - maybe being moved from the dropbox/files folder to the regular archive folder). Why it would have done this at 4am though is a mystery.
SO, the question, really, is: Is there something I need to be concerned about that this will happen again? What did Omeka think it was doing this morning? If I do only smaller (in MB at least) video files, should there be any sort of delayed movement (or any enormous movements that would concern by host)?

Omeka doesn't really have any time-delayed actions; it shouldn't be moving any files around by itself.

I assume the activity they were seeing was related to your initial attempts to upload very large videos. Even through the Dropbox, Omeka normally copies or moves a file to the temporary directory to work on it before moving it to the archive.