On the surface, iTunes 4 isn't a huge upgrade, but Apple wasn't content to let the application remain just a music player and encoder. As the iTunes Music Store's interface, iTunes has become a Web browser and an e-commerce engine. With new sharing capabilities, it's also a streaming server. Couple those features with added support for the Advanced Audio Coding (AAC) format, and it's clear that iTunes 4 is a must-have update for everyone who uses the program. Just keep in mind that this app runs only on OS X 10.1.5 or higher.

Let's Go Shopping

iTunes is still an excellent music encoder, organizer, and player, but it now wears an additional hat: iTunes 4 is also a music-store browser, accessible via the new Music Store item in iTunes' Source pane. And iTunes 4 even displays the cover art Apple includes with purchased tracks and albums. Click on the last icon in the lower left corner of iTunes to open the artwork window. To add your own artwork (something you downloaded from Amazon.com or a picture you scanned, for example), select an album or song and then drag the image onto the artwork window. In a small but nice touch, iTunes embeds the image in your music file, so the image stays attached when you move your music to another Mac.

AAC: Not Just for Playback Anymore

iTunes 3 could play several file types, including MP3 and the standard, unprotected AAC format. iTunes 4 can also encode music in the AAC format -- you just have to install the free QuickTime 6.2 update first.

Before iTunes 4, you could use the $30 QuickTime Pro 6 to encode one AAC file at a time. For batch encoding, you had to use another application. With iTunes 4, you can rip your CDs to AAC with the same simple tools you use for MP3 encoding -- and all iPods, with a free software update, can now play these files (for more on the new iPods, see "Third-Generation iPods"). iTunes 4 can even replace your old MP3 files with new AAC files you encode, and it keeps your song ratings, play counts, and other song data intact.

This new encoding option is a welcome addition. And when we encoded a track to both AAC and MP3, at the same bit rate, on a dual-867MHz G4, the file sizes were the same and took the same amount of time to encode, but the quality of the AAC file was higher.

All the World's Your Jukebox

One new feature we've enjoyed playing with here at the Macworld office is iTunes' library sharing. Once you enable the Share My Music option in the new Sharing pane of iTunes' preferences, Apple's Rendezvous technology lets other iTunes 4 users on your local network see your music. You can share individual playlists or your entire library, and you can password-protect your shared music to limit access -- you can't, however, store a password in your Keychain, so you have to enter it every time you connect to someone's shared music.

Using an IP address or domain name, you can also reach outside your network to connect to libraries on any Internet-connected Mac running iTunes 4 (Macs behind firewalls may have to open up port 3689 for this to work, and each server can have only five users at a time). Alas, iTunes doesn't let you bookmark other people's libraries; this can be frustrating when they're not on a local network and must be accessed manually. To circumvent this limitation, you can cre-ate an Internet Location file outside of iTunes and use it to connect to the iTunes-sharing computer. To create the file, type daap://serveraddress into just about any place you can enter text, select the text, and drag it to the desktop.

Once connected, you can listen to a streaming version of music in someone else's library, but you can't copy the actual files. Although people viewing your library can see MP3 files, standard AAC files, and the protected AAC files purchased from the iTunes Music Store, they can't play the Music Store tracks unless you authorize their Mac with your Apple login and password. We understand why Apple made this choice, but it does make for an aggravating experience: since you can't tell a file's type by looking at it in an iTunes library, you can't know which songs you can listen to until you try.

If you like applications such as Synergy or Kung-Tunes, which work with iTunes to display currently playing tracks in separate windows, you're out of luck. These tools don't work when you're listening to songs from other people's libraries.

Small Improvements

Previous versions of iTunes had a Search box, but you couldn't specify which tags -- information stored with a file -- you wanted to search. iTunes 4 lets you search by artist, album, composer, and song: click on the magnifying-glass icon in the Search box.

iTunes' Burning preference pane has a new option called Data CD (Data CD Or DVD if you have a DVD-RW drive) that lets you burn a Mac-formatted data disc containing the files in a playlist. When combined with iTunes' Smart Playlist feature, this makes backing up or moving files to another Mac an easier task.

Finally, Apple has added a Beats Per Minute (BPM) field, so DJs who enter this information can use it for mixing songs together.

Potential Problems

You may come across a few annoyances after upgrading. For example, because iTunes now pays attention to your systemwide font settings, track information may look a bit fuzzy. You can fix this by adjusting your font-smoothing settings in the General pane in OS X's System Preferences.

It should also be noted that some people have experienced muffled sound and volume adjustments after upgrading from iTunes 3. We haven't experienced any such problems.

Macworld's Buying Advice

Anyone who's interested in improved sound quality with AAC files, who wants to browse and buy from the iTunes Music Store, or who'd like to share and access other people's iTunes music should download iTunes 4.