Warning when opening .mp4 video files

["Jasper Thrussell" <j thrussell gmail com>]

Whenever I double click on a .mp4 video file in nautilus the following
warning message is displayed:

"The filename "test.mp4" indicates that this file is of type "mp4
document". The contents of the file indicate that the file is of type
"MPEG-4 video". If you open this file, the file might present a
security risk to your system.

Do not open the file unless you created the file yourself, or received
the file from a trusted source. To open the file, rename the file to
the correct extension for "MPEG-4 video", then open the file normally.
Alternatively, use the Open With menu to choose a specific application
for the file. "

Now as far as I know, .mp4 is the correct extension for MPEG4 video
files (I've never heard of a .mp4 document file), so how can I get
nautilus to open the file rather than displaying the warning message?

Using the "open with" command works fine, but it's annoying to have to
do that every time.