i did, same length on computer. also one other video seems to have been snipped too but only maybe one second but this one is somewhere between 20-30.
i guess the lesson is to either do not rename the file on the device or backup images and videos yourself since backup app doesnt.
the same happened to me, but not using the n900. what i did was i tried to convert the video then play it again, was okay, then convert it back to the original file format.
hope this helps