ltjfansite:
Perhpaps saying we do not support but the current release is a bit incorrect. You will find we do all sorts of help for people running older versions. However we will not make corrections to any but the current release. So if you have a problem that requires a change to Zenphoto you will have to either live with it or upgrade. That is, of course, your choice.
Now then, there have been some fixes to problems with video since the 1.2.9 release. If your problem is caused by one of the bugs that has been fixed, well, see above.
If it is someting else, for instance Acrylian's suggestion that you check to be sure that A/ you have the class-video plugin enabled and B/that the video format you uploaded (and neglected to mention) is supported by either the class-video plugin or by your browser [it depends on the format which is required.]