AudioMetaTagger: recursively read files and gather metadata
welcome to code review! Here are some thoughts:

Casting

To get rid of the casting you can use generics (see also: https://docs.oracle.com/javase/tutorial/java/generics/types.html) like so:

public static Collection&lt;File&gt; checkData(File dir){
    Collection&lt;File&gt; files = FileUtils.listFiles(
        dir, 
        new RegexFileFilter("^(.*mp3)"), 
            DirectoryFileFilter.DIRECTORY
        );
    return files;
}


This way in your main function you can avoid the casting:

 Collection&lt;File&gt; files = checkData(dir);
 for(File file: files) {


This is to be preferred, as casting is to be avoided when possible (Interesting related discussion: https://stackoverflow.com/questions/4167304/why-should-casting-be-avoided).

Code

Why initialize a variable first and then assign the value? You can easily do it in one line, which is nicer to read:

AudioFile audioFile = AudioFileIO.read(file);


Formatting

On the nitpicky side, you should take a look at how code formatting is usually done in java: https://docs.oracle.com/javase/tutorial/essential/io/formatting.html 

Using decent indentation and spacing allows for easier reading of the code. The best advice here is probably using the auto-formatter of your IDE (eclipse, intelliJ, etc.), as it is tedious to do it by hand.

Performance

Judging from your code, I don't see any specific place to make it a lot faster using the library. It looks like the library reads the entire file to get the metaData, which is of course very I/O intense, and therefor slow. 
More advanced libraries like JAudioTagger (http://www.jthink.net/jaudiotagger/examples_read.jsp) might be able to do this in a more efficient way.

Hope this helps!