DYI repairs (do-it-yourself) are rare cases where, without deep knowledge of the subject, one can repair a corrupt movie file.
Don't get me wrong, I am not under-estimating my readership!
It's just that to repair a movie file is a very complex task that requires several years of experience in very demanding and inscrutable fields: Audio and Video encoding, QuickTime programming, ...
In general, you will not be able to repair a corrupt movie. Unless you are willing to spend several years learning (Did I mention that there is no school teaching that stuff? This guide is probably the most comprehensive resource about the topic publically available, anyway).
That is the raison d'ĂȘtre of my business, after all!
But in rare cases it's possible.
Note that I don't say easy or funny: You will have to put your hands in dirt, spend (waste?) a lot of time, and at the end it may or may not work. Even for technically capable people.
Last disclaimer:
The rare cases below are nearly indistinguisable from the common cases where a DYI repair method will not work. You have been warned!
DYI Techniques
Container Structure Correction
Repairing AIFF files
Fixing a missing resource fork
The mythical "fix by replacing damaged/missing moov atom by the moov atom of a good file" will only work in very rare situations. If the file contains audio or other video than a fixed-frame length format, then it cannot work.
See also http://echoone.com/filejuicer/formats/mov-repair