How to determine file type?

Question

I need to know if my file is audio file: mp3, wav, etc...
How to do this?

Answer 1

Well, the most robust way would be to write a parser for the file types you want to detect and then just try – if there are no errors, it's obviously of the type you tried. This is an expensive approach, however, but it would ensure that you can successfully load the file as well since it will also check the rest of the file for semantic soundness.

A much less expensive variant would be to look for “magic” bytes – signatures at the start or known offsets of the file. For example, if a file starts with an ID3 tag you can be reasonably sure it's an MP3 file. If a file starts with RIFF¼↕☻ WAVEfmt, then it's a WAV file. However, such detection cannot guarantee you that the file is really of that type – it could just be the signature and following that garbage.

Answer 2

While you can use the extension to make a reasonable guess as to what the file is it's not guaranteed to work 100% of the time. If you are targeting Windows then it will work 99.9% of the time as that's how Windows keeps track of what file is what type.

If you are getting your files from non-Windows sources the only sure way is to open the file and look for a specific string or set of bytes which will unambiguously identify it. For example, you could look for the ID3 tags in an mp3 file:

The ID3v1 tag occupies 128 bytes, beginning with the string TAG.

or

ID3v2 tags are of variable size, and usually occur at the start of the file, to aid streaming media.

How far you go depends on how robust you want your solution to be, and does rely on there being a header or pattern that's always present.

Doing it this way can help guard against malicious content where someone posts a piece of malware as a mp3 file (say) and hopes that it will just be run by a program prone to some exploit (a buffer overrun perhaps).

Answer 3

You can use the file extension to figure it out:

using System.IO;

class Program
{
    static void Main()
    {
        string filepath = @"C:\Users\Sam\Documents\Test.txt";

        string extension = Path.GetExtension(filepath);
        if (extension  == ".mp3")
        {
            Console.WriteLine(extension);
        }
    }
}

The file extension is the first point of call for the OS to figure out what file type it's dealing with, if you really want to know the file type 100% the only way to do it is read into the file. But this comes with a catch, image files are easy as they include headers in a pretty easy to read format, however it can get a little more complex with a completely variable file type.

You could check out this post on an old post for a bit of help. Here is a post about finding just media file types.

Ultimately it depends on why your trying to do this.

Answer 4

Path.GetExtension(PathToFile)

Answer 5

See this post. You end up passing the first (up to) 256 bytes of data from the file to FindMimeFromData (part of the Urlmon.dll).