How do you check a file type when there is no extension in c#

Question

How do you check a file type when there is no extension in c#

For instance, I have files with no extension, that are either .mp4 or .flv format (just no extension).

Answer 1

I had played this utility (TrID - File Identifier) and seems quite accurate. File type defination package (TrIDDefs) is also up to date.

And Here is a list of file type signature table if you interest. The list is continuing work-in-process.