I have downloaded a file which is supposed to be an AVI, but it says "Format unknown" when it is played. How can I find out what is its extension? I've tried without success using Gspot.
In order to check the file format of your video file, just right-click its icon and select Properties. Click the General tab and you will find the file format next to Type of file. If it displays unknown format, try scanning your file using TrIDNet or FileType Identifier. The last one is a free of charge tool that can be downloaded from Google Code page.
