If you're reasonably close to a modern Linux system, try the file command. It's pretty well-educated:
~> file foo.mov
foo.mov: ISO Media, Apple QuickTime movie
~> mv foo.mov whatever
~> file whatever
whatever: ISO Media, Apple QuickTime movie
As you can see, it checks the contents of the file, it doesn't just test the filename. Not implying that the tool you tried was reliant on the filename, just trying to illustrate that it can be a powerful tool.