Not every household needs more than one computer running iTunes. In fact, as it becomes more common to stream music and videos to connected devices throughout the house, more homes may have just one PC. As that happens, you'll need to know how to consolidate iTunes libraries from multiple machines into a single, large iTunes library on the new computer.
Due to the large size of most iTunes libraries, consolidating them isn't as simple as burning a CD and loading it on the new computer. Luckily, there are a number of methods--some free, some with small costs--that can make this process easier.
Home Sharing, available in iTunes 9 and higher, allows iTunes libraries on the same network to copy items back and forth. This works on up to 5 computers and requires that they sign into iTunes using the same iTunes account.
To consolidate libraries, turn on Home Sharing on all the computers you want to merge and then drag and drop the files to the computer that will store the merged library. You'll find the shared computers in the left-hand column of iTunes. Home Sharing does not transfer star ratings or playcounts for music.
Some apps will copy via Home Sharing, some may not. For ones that don't, you can redownload them onto the merged library for free.
2. Transfer Purchases from iPod
If your iTunes library comes primarily from the iTunes Store, try this option. The drawback is that it probably won't work for everything (most people have music from CDs and other stores), but it can reduce the transferring you need to do in other ways.
Start by signing the computer that will have the shared iTunes library into the iTunes account associated with the iPod. Then connect the iPod to the computer.
If a window pops up with a "Transfer Purchases" button, click that. Do not choose "Erase and Sync"--you'll erase your music before you move it. If the window doesn't appear, go to the File menu and choose "Transfer Purchases from iPod."
The iTunes Store purchases on the iPod will then move to the new iTunes library.
3. External Hard Drive
If you store your iTunes library, or back up your computer, on an external hard drive, consolidating libraries is easier.
Plug the hard drive into the computer that will store the new iTunes library. Find the iTunes folder on the external hard drive, and the iTunes Music folder inside it. This contains all music, movies, podcasts, and TV shows.
Select the folders that you want to move from the iTunes Music folder (this is usually the entire folder, unless you want to select only certain artists/albums) and drag them to the "Library" section of iTunes. When that section turns blue, the songs are moving to the new library.
NOTE: using this method, you will lose the star ratings and playcounts on the songs being moved to the new library.
4. Library Sync/Merge Software
There are a few third-party software programs that willmake the process of merging iTines libraries easier. Among the key features of these programs are that they will retain all of the metadata--star ratings, playcounts, comments, etc.--that are lost using other transfer methods. A few of the programs in this space include:
If your entire iTunes library is synced to your iPod or iPhone, you can move it from your device to the new merged iTunes library using third-party software.
There are dozens of these iPod copying programs--some are free, most cost US$20-$40--and all do essentially the same thing: copying all the music, movies, playlists, star ratings, playcounts, etc. on your iPod, iPhone, or iPad to a new iTunes library. Most don't transfer apps but, as noted above, you can always redownload apps to the new iTunes library.
Unlike the external hard drive method above, these programs let you retain star ratings, playcounts, playlists, etc.
6. Online Backup Services
You do back up all your data, right? (If you don't, I'd recommend starting before a hard drive failure makes you sorry you didn't. Check out the top 3 backup services for a starting point.) If you use an online backup service, merging iTunes libraries can be as simple as downloading the latest backup from one computer to another (if your library is very big, you may want to use DVDs with your data on them that some services offer).
Whether you download or use a DVD, use the same process as with external hard drives to move your old iTunes library to the new one.
7. Create a Local Network
If you're a more technically advanced user (and, if you're not, I'd recommend trying all the other options before you try this one), you may want to just network to computers together so you can drag and drop the iTunes files you want to consolidate from one machine to the other. When doing this, follow the instructions from the external hard drive option above to make sure you combine libraries, rather than erase one with the other.
8. Dealing with Apps, Movies/TV
All the contents of your iTunes library--apps, movies, TV, etc.--are stored in your iTunes library, not just music. You can find these non-music items in your iTunes folder (in the My Music folder). The Mobile Applications folder contains your apps, and you'll find folders called Movies, TV Shows, and Podcasts in the iTunes Media folder containing those items.
While some iPod copying software won't transfer all of these kinds of files (especially if they're not all on your iPod, iPhone, or iPad when you try to copy it), the methods above that include drag-and-drop copying of files from one iTunes folder to another will move these non-music files, too.
9. Consolidate/Organize Libraries
After you've moved the files from your old iTunes library to the new, merged one, take these two steps to make sure that your new library is optimized and stays that way. This is called consolidating or organizing your library (depending on your version of iTunes).
First, consolidate/organize the new library. To do that, go to the File menu in iTunes. Then go to Library -> Organize (or Consolidate) Library. This optimizes the library.
Next, ensure that iTunes is set to always organize/consolidate your new library. Do this by going to the iTunes Preferences window (under the iTunes menu on a Mac, under Edit on a PC). When the window appears, go to the Advanced tab. There, check the "Keep iTunes Media folder organized" box and click "OK."
Lastly, to ensure that your new iTunes library can play everything in it, you need to authorize the computer to play the music you've transferred.
To authorize the computer, go to the Store menu in iTunes and choose "authorize this computer." When the iTunes account sign-in window pops up, sign in using the iTunes accounts from the other computers merged to the new one. ITunes accounts have a maximum of 5 authorizations (though one computer can have multiple account authorizations), so if you've authorized 5 other computers to play content, you'll need to de-authorize at least one.
Before you get rid of the old computer that you moved the iTunes library from, be sure to de-authorize it to preserve your 5 authorizations.