under more info it just says when it was last opened.
Then I would move on to the VLC Player which contains its own codec and does not depend on the QT components. It tends to open many files using codecs primarily associated with "Windows" codecs, transport streams, and the like. If it open in that app, look in the "Window > Media Information..." window and see what codecs it says the file contains. If that doesn't work, post a sample file for examination by one of this forums' regular contributors.