Not sure if this is the place to provide this, but I can't find anywhere else.
I've discovered a Bug in Windows Live Photo Gallery that is corrupting .3gp files. It seems as though it is not updating the header information correctly if metadata is added to the file. About 90-95% of the time if I add a caption and a person tag, the
movie becomes unplayable. It can sometimes take a while to become corrupt, which I assume is the delay in the program writing out the MetaData.
The file will either come up with the message "windows encountered a problem playing the file" or only audio will play. This may also answer a lot of the other issues people have raised with not playing .3gp files on the forum.
This is on Windows 7, 64Bit and is only happening with movie files in the .3gp format.