For reasons that aren't entirely obvious, there are a remarkable number of different audio file formats available for computers, and even "MP3" isn't entirely consistent, with different compression rates, sampling rates, etc. You don't usually have to worry about any of it, but for some audio purists, they don't like the idea that a file has been reduced in size by compressing the content. They want "every bit" of digital music.

Enter FLAC, or "Free Lossless Audio Codec", a format that is designed to retain all of the original music data and, even better, is license and restriction free (the MP3 format requires a license to use, though it's obviously widely licensed). If you're developing softare and want to just do your thing and not worry about licenses, FLAC is a good audio file format.

Except it doesn't work with iTunes, which prefers two formats; Apple's AAC format, and the ubiquitous MP3 format. No FLAC. So what you're left with is having to convert the audio files your friend sent you from FLAC format to MP3 format.

There are a bunch of tools that can perform this task, but one of my new favorites is a simple, fast app called ALL2MP3. It offers a nice front-end to some scripts that do the work, but you don't have to worry about that. You can download it through CNET: Download ALL2MP3.

Once downloaded, launch the app, and make sure you can see your FLAC audio file and the app window both:

Now just select the files you want to convert and drag them all onto the app window:

When you release the button, the app will absorb all the files and change its appearance to show what's about to be converted:

See that "Trash files after conversion" on the lower right? I suggest you check the box and then it really will be magic as the .flac files turn into .mp3 files with exactly the same names.

When you're ready to go just click on "Convert" and it'll start the conversion process:

When it's done, go back and look at your original folder full of ".flac" files and they'll all have been replaced with their MP3 equivalents:

Now to add them to your ITunes library, you can just drag them en-masse to the iTunes window:

That's it. Nice and straightforward. And better yet, ALL2MP3 is freeware too.