iTunes ( /ˈaɪtjuːnz/ or /ˈaɪtuːnz/ ) is a media player, media library, online radio broadcaster, and mobile device management application developed by Apple Inc. It is used to play, download, and organize digital downloads of music and video (as well as other types of media available on the iTunes Store) on personal computers running the macOS and Microsoft Windows operating systems. The iTunes Store is also available on the iPhone, iPad, and iPod Touch.
Through the iTunes Store users can purchase and download music, music videos, television shows, audiobooks, podcasts, movies, and movie rentals (in some countries), available on the iPhone and iPod Touch (fourth generation onward). Application software for the iPhone, iPad and iPod Touch can be downloaded from the App Store. iTunes 12.5 is the most recent major version of iTunes, available for Mac OS X v10.9.5 or later and Windows 7 or later; it was released on September 13, 2016.  iTunes 12.2 added Apple Music to the application, along with the Beats 1 radio station, and iTunes 12.5 offers a refinement of the Apple Music interface.
In the latest version of iTunes released on September 12, 2017 (iTunes 12.7), Apple removed the App Store and Ringtone section of the software. iTunes U was also merged with the podcasts section.  On September 22, 2017, Apple released a special fork of iTunes (18.104.22.168) that reintroduces the ability to access the App Store for enterprise customers, while adding support for iOS 11 and macOS High Sierra. 
SoundJam MP, developed by Bill Kincaid and released by Casady & Greene in 1998,  was renamed iTunes when Apple purchased it in 2000. Jeff Robbin, Kincaid, and Dave Heller moved to Apple as part of the acquisition, where they continue to work today as the software's original developers. They simplified SoundJam's user interface, added the ability to burn CDs, and removed its recording feature and skin support.  On January 9, 2001, iTunes 1.0 was released at Macworld San Francisco. 
iTunes acts as a front end for Apple's QuickTime media framework.  Officially, it is required in order to manage the audio data of an iPod, iPhone, or iPad, although alternative software does exist. Users can organize their music into playlists within one or more libraries, edit file information, record Compact Discs, copy files to a digital audio player, purchase music and videos through its built-in music store ( iTunes Store), download free podcasts, back up songs onto a CD or DVD, run a visualizer to display graphical effects in time to the music, and encode music into a number of different audio formats. 
In addition, users are able to add PDF files to their library.  The PDFs can be synchronized with and read on several devices except the regular iPod.   iTunes 8.0 saw the removal of several options in the Preferences window. For example, iTunes once gave users the option to display arrows beside the selected song's title, artist, album, and genre that link directly to the iTunes Store. These arrows are no longer removable, except through the direct editing of a preferences file. 
iTunes keeps track of songs by creating a virtual library, allowing users to access and edit a song's attributes. These attributes, known as metadata, are stored in a binary library file called iTunes Library , which uses a proprietary file format ("ITL"). It caches information like artist and genre from the audio format's tag capabilities (the ID3 tag, for example) and stores iTunes-specific information like play count and rating. iTunes typically reads library data only from this file.  A second file can also be created if users activate a preference; the iTunes Music Library.xml file is refreshed whenever information in iTunes is changed. It uses an XML format, allowing third-party apps to access the library information (including play count, last played date, and rating, which are not standard fields in the ID3v2.3 format). Apple's own iDVD, iMovie, and iPhoto applications all access the library.  If the first file exists but is corrupted, such as by making it zero-length, iTunes will attempt to reconstruct it from the XML file. Detailed third-party instructions regarding this can be found elsewhere.  Beginning with iTunes 10.5.3 this behavior has been changed such that the XML file is not read automatically to recreate the database when the database is corrupted. Rather, the user should load the iTunes Library.xml file via File > Library > Import Playlist....
It has also been noted that iTunes does not automatically track changes to actual files in the library. If a file is moved or deleted, iTunes will display an exclamation mark beside the library entry and the user will need to manually amend the library record. Several third party tools address this problem. 
iTunes supports ripping from CDs, but not from DVDs. However, in 2008, Apple and select film studios introduced "iTunes Digital Copy ", a bonus feature on some DVDs that provides a copy-protected and iTunes-compatible file for select films. 
Audio file format support
iTunes can also play any audio files that QuickTime can play (as well as some video formats), including Protected AAC files from the iTunes Store and Audible.com audio books. Because tag editing and album art is done within iTunes and not QuickTime, these features will not work with these QuickTime components. As of Snow Leopard, iTunes 9 (Mac) will play HE-AAC / AAC+ internet streams. The latest version of iTunes (Win/Mac) supports importing audio CDs using any of the standard audio file formats iTunes supports (AIFF, WAV, Apple Lossless, AAC, MP3), with the AAC and MP3 available in constant bit rate (CBR) or variable bitrate (VBR) encoding.
The Windows version of iTunes can automatically transcode DRM-free WMA (including version 9) files to other audio formats, but does not support playback of WMA files and will not transcode DRM protected WMA files. Telestream, Inc. provides free codecs for Mac users of QuickTime to enable playback of unprotected Windows Media files. These codecs are recommended by Microsoft. 
In addition to importing CDs into the iTunes library, users can also import digital audio files from other sources, in any format that iTunes supports. This can be accomplished by either right clicking on the file, selecting open with, and then selecting iTunes or dragging the file into the open iTunes window. Alternatively, for Amazon.com MP3 files, the Amazon MP3 Downloader application will automatically import the files into the iTunes library. 
For MP3 files, iTunes writes tags in ID3v 2.2 using UCS-2 encoding by default, but converting them to ID3v2.3 (UCS-2 encoding) and ID3v2.4 (which uses UTF-8 encoding) is possible via its "Advanced" > "Convert ID3 Tags" toolbar menu. If both ID3v2.x and ID3v1.x tags are in a file, iTunes ignores the ID3v1.x tags. 
Advanced Audio Coding and Apple Lossless files support Unicode metadata, stored in the MPEG-4 Part 14 container as so-called "atoms". iTunes uses the Gracenote interactive audio CD database to provide track name listings for audio CDs. The service can be set to activate when a CD is inserted into the computer and an Internet connection is available. Track names for albums imported to iTunes while not connected to the Internet can be obtained during a later connection, by a manual procedure.  For any album loaded into iTunes for which there is not an existing Gracenote track listing, the user can choose to submit track name data to Gracenote. 
File metadata is displayed in columns, including album, artist, beats per minute, bit rate, composer, date added, date modified, disc number, genre, last played, last skipped, plays, purchase date, size, skips, time, track number, year, and a few fields that may be supplied by users, such as description, kind, and rating. Metadata fields not loaded with the song, or added by a user, remain blank. 
iTunes utilizes a special ID3 tag in order to display an Explicit or Clean tag on songs purchased from the iTunes store. Unlike most other tags, the tag cannot be changed within iTunes. It can be changed or added to AAC files in third party software.
The Genius feature, introduced in iTunes 8, automatically generates a playlist of songs from the user's library which are similar to the selected song. Genius playlists are created by the ratings system and collaborative filtering. An iTunes Store account is required because information about the user's library must first be sent anonymously to Apple's database. Algorithms determine which songs to play based on other users' libraries, and Genius becomes more intelligent given a larger data set. The resulting Genius playlist can contain 25, 50, 75, or 100 songs and can be refreshed for new results or saved. Once Genius becomes active in iTunes, it can be used on current generations of the iPod Classic, iPod Nano, iPod Touch or the iPhone.  iTunes 9 added Genius Mixes, where the Genius software finds similar music and automatically puts them into mixes.  iTunes Genius creates playlists from the user's existing iTunes library based on a single selected song. Genius Mixes create playlists based on the musical genre.
One way of sharing a library is over the network, known as network sharing. A user's iTunes Library can be shared over a local network using the closed, proprietary Digital Audio Access Protocol (DAAP), created by Apple for this purpose. DAAP relies on the Bonjour network service discovery framework, Apple's implementation of the Zeroconf open network standard. Apple has not made the DAAP specification available to the general public, only to third-party licensees such as Roku. However, the protocol has been reverse-engineered and is now used to stream audio from non-Apple software (mainly on the Linux platform).  DAAP allows shared lists of songs within the same subnet to be automatically detected. When a song is shared, iTunes can stream the song but won't save it on the local hard drive, in order to prevent unauthorized copying. Songs in Protected AAC format can also be accessed, but authentication is required. A maximum of five users may connect to a single user every 24 hours. The multiple, alternate "View" options normally available to iTunes users including "Cover Flow" are disabled when viewing a shared library over a network. In the period before the arrival of inexpensive streaming services, local network streaming was a popular feature among user groups such as college students connecting their own computers on a local network.
Library sharing was introduced with iTunes 4.0, where users could freely access shared music anywhere over the Internet, in addition to one's own subnet, by specifying IP addresses of remote shared song libraries. Apple quickly removed this feature with version 4.0.1, claiming that users were violating the End User License Agreement. 
With the release of iTunes 7.0, Apple changed their implementation of DAAP. This change prevents any third-party client, such as a computer running Linux, a modified Xbox, or any computer without iTunes installed, from connecting to a remote iTunes repository. iTunes will still connect as a client to other iTunes servers and to third-party servers. 
iTunes libraries can also be shared using the “Home Share” option. This option enables users to share both video and audio files through the application. This allows users to also look for items that they don’t already have.  Like network sharing, it allows users to share over the same network to up to five computers. The media can then be transferred to any type of iPod or iPad. To set up home sharing, the two computers being used must be on the same network as well as set up using the same Apple ID.
Another option to share music files is to burn CDs. To do this the user needs to create a playlist with the songs the user wishes to share. If the playlist exceeds roughly twenty songs it is likely they will need to make multiple CDs. By inserting a disk into the disk drive a button on the bottom of the window should give the option to burn a disk. The files are automatically downloaded to the disk and may be uploaded onto another computer or saved as a backup for the user’s computer.
iTunes allows users to choose different ways to categorize their collection, and displays content according to the selection. The default settings show the music collection sorted by album, laying out the artwork in a grid similar to the iPad Music app (iOS 3.1-6.1.3, 8.4). When selected, albums extend downwards, showing their contents, and allowing users to browse the store for missing or related content. The content listings are themed depending on the predominant color of the album artwork. Film and television shows are laid out in the same manner, with their posters or artwork laid out in a grid. Users may alternately arrange their music collection as a list of every song, by genre, or by artist. These show details in a list structure, but the latter two include the album artwork as thumbnails to aid navigation. Items are automatically arranged alphabetically by album name, but users may rearrange this if using the song list option.
iTunes 11 removes the Cover Flow option, previously the default viewing method for a user's music collection. It also disables the sidebar by default, focusing on spreading content across the width of the window. The status bar is also disabled by default. Both of these may be reactivated by the user. The sidebar design has been slightly altered, reinstating the colored icons removed in iTunes 10. When the sidebar is not activated, users can move between media libraries using a drop down menu below the control buttons.
In addition to static playlist support, version 3 of iTunes introduced support for smart playlists.  Smart playlists are playlists that can be set to automatically filter the library based on a customized list of selection criteria, much like a database query. Multiple criteria can be entered to manage the smart playlist. 
Some automatic smart playlists that are added to the user’s library include Top 25 Most Played, Recently Played, Recently Added, My Top Rated, Music Videos, Classical Music, Purchased, and 90’s Music. While creating Smart Playlists the user has to choose whether they want the playlist to be based on genre, whether or not the songs have album artwork, date added, etc. and if they want it to contain or not contain certain genres or artists. For example, a genre like country music, or songs added in a specific month or year, or an individual artist. The user can also limit the amount of songs they want in the playlist or they can leave it as unlimited. The Live Updating option will automatically update their new playlist as their library changes. 
Introduced in iTunes 4.5,  the "Party Shuffle" playlist was intended as a simple DJing aid.  By default, it selects tracks randomly from other playlists or the library, but users can override the automatic selections by deleting tracks (iTunes will choose new ones to replace them) or by adding their own via drag-and-drop or contextual menu. This allows a mixture of both pre selected and random tracks in the same meta-playlist. The playlist from which Party Shuffle drew could be changed on the fly by the computer user, but doing so will cause all randomly chosen tracks to disappear and be replaced.
Party Shuffle was renamed iTunes DJ in iTunes 8. When iTunes was updated to 8.1, quite a few features were added to iTunes DJ. The free Apple Remote application for the iPhone and iPod Touch was also updated at this time that added a new iTunes DJ option in the settings screen when the user is connected to a Wi-Fi network and a new song request feature is enabled in iTunes DJ on the hosts. Along with the song request feature voting on songs in the queue was added, the more votes a song gets the higher in the queue it will be and the sooner it will be played. Song voting can only be done when song requesting is enabled and in two ways: the first by right clicking on a song in the iTunes DJ queue on the host's computer in iTunes, the second is in the Remote application ether connected with the iTunes DJ option by a guest or by the host in the full playlist section. When song requesting is enabled a customizable welcome message is displayed below the host's shared library name in the button used to connect to iTunes DJ. 
Playlists can be played randomly or sequentially. The randomness of the shuffle algorithm can be biased for or against playing multiple tracks from the same album or artists in sequence (a feature introduced in iTunes 5.0, and later discontinued in iTunes 8.0). iTunes DJ can also be biased towards selecting tracks with a higher star rating.
With the release of iTunes 11, the iTunes DJ feature was removed in favor of the Up Next feature, which allows users to specify a song from their collection to play next, add it to a queue of songs to be played, or view a list of previously played tracks. However, the Up Next feature does not include features that used to be found in iTunes DJ, such as the ability for guests to request songs, does not provide as much information as the playlist view, and requires juggling multiple windows and floating dialogs to perform similar tasks.
To compensate for the lack of a physical CD, iTunes can print custom-made jewel case inserts as well as song lists and album lists. After burning a CD from a playlist, one can select that playlist and bring up a dialog box with several print options. The user can choose to print either a single album cover (for purchased iTunes albums) or a compilation cover (for user-created playlists). iTunes then automatically sets up a template with art on one side and track titles on the other. 
iTunes includes sound processing features, such as equalization, "sound enhancement" and crossfade. There is also a feature called Sound Check , which automatically adjusts the playback volume of all songs in the library to the same level; this is usually called volume leveling or audio normalization. Like "sound enhancement" and crossfade, this can be turned on in the Playback section of iTunes' preferences.
On May 9, 2005, video support was introduced to iTunes with the release of iTunes 4.8. Users can drag and drop video clips from the computer into the iTunes Library for cataloging and organization. They can be viewed in a small frame in the main iTunes display, in a separate window, or full screen. Before version 7 provided separate libraries for media types, videos were only distinguished from audio in the Library by a small icon resembling a TV screen and grouped with music in the library, organized by the same musical categories (such as "album" and "composer").
On October 12, 2005, Apple introduced iTunes 6.0, which added support for purchasing and viewing of video content from the iTunes Music Store. The iTunes Music Store initially offered a selection of thousands of Music Videos and five TV shows, including most notably the ABC network's Lost and Desperate Housewives . Disney Channel shows ( The Suite Life of Zack & Cody and That's So Raven ) were also offered 24 hours after airing, as well as episode packs from past seasons. Since then, the collection has expanded to include content from numerous television networks. The iTunes Music Store also gives the ability to view Apple's large collection of film trailers.
As of September 5, 2006, the iTunes Store offers over 550 television shows for download. Additionally, a catalog of 75 feature-length films from Disney -owned studios was introduced. As of April 11, 2007, over 500 feature-length films are available through iTunes. 
Originally, films and TV shows were only available to U.S. customers, with the only video content available to non-U.S. customers being music videos and Pixar's short films. This feature is being extended to other countries as licensing issues are resolved.
Video content available from the store used to be encoded as 540 kbit/s Protected MPEG-4 video ( H.264) with an approximately 128 kbit/s AAC audio track. Many videos and video podcasts require the latest version of QuickTime, QuickTime 7, which is incompatible with older versions of Mac OS (only v10.3.9 and later are supported). On September 12, 2006, the resolution of video content sold on the iTunes Store was increased from 320×240 ( QVGA) to 640×480 ( VGA). The higher resolution video content is encoded as 1.5 Mbit/s (minimum) Protected MPEG-4 video ( H.264) with a minimum 128 kbit/s AAC audio track.
Video file format support
iTunes supports MP4, M4V and MOV files.
In September 2006, iTunes started to sell full-length films.  This entails downloading movies from the iTunes store. The prices for these range from: $9.99, $14.99 if it is a new release, and $19.99 if it is in High Definition.  iTunes also gives the option of renting movies, which began in January 2008.  The price for renting a movie can range from $0.99 if the movie is on sale, $3.99, and $4.99 if the rental is HD. However, iTunes sometimes carries, for a limited time, movies to rent that are available OnDemand, for a price of $6.99 in both SD and HD. Once a rental is downloaded the viewer has thirty days to watch the movie before it expires. Once the viewers begin to watch the movie they have 24 (in the US) or 48 hours to finish the movie before it expires. Movies can be organized in the iTunes library by title, genre, or unwatched.
In October 2005, the iTunes Store began to offer the option of downloading television shows in some, not all, markets.  iTunes offers the option of buying individual episodes of TV shows for $1.99 in standard definition or $2.99 in high definition. The high definition feature on TV shows was added in July 2008.  iTunes also offers the ability to buy a season pass for television shows. This allows viewers to buy an entire season that automatically downloads new episodes around twenty-four hours after they air. In the iTunes library, these shows are then categorized by season of the particular show. iTunes also gives the option of ordering shows based on: series, genre, or whether or not the episodes are unwatched. In fall of 2010 iTunes offered TV show rental options, but as of August 2011 this option is no longer offered. 
Version 4.9 of iTunes, released on June 28, 2005, added built-in support for podcasts. 
Users can subscribe to any podcast by entering its RSS feed URL, but also by browsing the podcast directory within the iTunes Store. The front page of this displays high-profile podcasts from commercial broadcasters and independent podcasters and allows searching by category or popularity. Once subscribed, the podcast can be set to download manually, or automatically — and as with other audio, content can be listened to directly or synced to a portable hardware device like an MP3 player.
The addition of podcasting functionality to such a widespread audio application like iTunes greatly helped podcasting enter the mainstream.  Within days after iTunes 4.9 was released, podcasters were reporting that the number of downloads of their audio files had tripled, sometimes even quadrupled,  and iTunes is considered the dominant podcast client.
Users can subscribe to RSS feeds through the iTunes Store or by directly entering the feed URL. Video podcasts can contain downloadable video files (in MOV, MP4, M4V, or MPG format), but also streaming sources and even IPTV. 
iTunes offers the ability to create "Smart Playlists" that can be used to control which podcasts are in the playlist, using multiple criteria such as date, number of times listened to, type, etc. It is also possible to set up iTunes so that only certain playlists will be synced with the iPod. By using a combination of the two techniques, it is possible to control exactly which music and/or podcasts will be transferred to the iPod. A user may configure a smart playlist to display only podcasts less than two weeks old or removing any podcast that the iPod user has already listened to. This smart playlist is synced with the iPod every time the iPod is plugged into the PC, ensuring that the user does not have to listen to the same show more than once. Once a podcast has been listened to, it will be removed from this list as soon as the iPod is synced with the PC. There are many criteria which can control what goes in a smart playlist, such as "name", "artist", "category", "grouping", "kind", "last played", "play count", "rating", "last skipped", and "playlist" and these can be combined with functions such as "equals", "is greater than", "is less than", "contains", "does not contain", "is true", "is false", "is", "is not", "starts with", "ends with", "is in the range", "is before", and "is after". As a result, it is possible to control exactly which podcasts are transferred to the iPod.
In February 2010, Apple announced the release of the iPad, and along with it a new app for it called iBooks. The application performs two functions. The first function is as a direct link to the iTunes book store, called iBooks Store , which can be accessed on iOS devices and computers (Mac or PC). The second was as a storage place for downloaded books (whether free or purchased) from the iBooks Store. The format of books from the Apple store (and the only one users could use with iBooks until PDF functionality was added later) is ePub.
Additional functions were later added in mid-2010 to include annotations and placeholders/bookmarks in any book. Also PDF documents were able to be added, and were stored under their own tab in a user's iBooks library, with the same functionality. The iBooks app for the other two iOS devices (iPhone and iPod Touch) was released when iOS 4 was distributed shortly before the release of the iPhone 4.
Until the release of OS X 10.9 Mavericks in October 2013, books (though not PDF documents) could only be read using the app on any iOS device and not on a user's Mac or PC. With the release of Mavericks, Apple released a standalone iBooks app for OS X, which moved books from the iTunes library, and allows Mac users to read these books on their Macs. PDF documents can be read using Preview or any other PDF reader/editor application the user has on their machine.
The App section on iTunes kept track of all of the apps the user has downloaded or purchased. It also organized their apps by genre, and there was another tab that let the user see all of their apps. It also informed the user when they have updates available for their apps. The app store part of iTunes was removed in iTunes version 12.7. On September 22, 2017, Apple released a special fork of iTunes (10.6.3) that reintroduces the ability to access the App Store for enterprise customers, while adding support for iOS 11 and macOS High Sierra. 
Version 4 of iTunes introduced the iTunes Store, then named the iTunes Music Store, from which iTunes users can buy and download songs for use on a limited number of computers and an unlimited number of iPods. In previous years, purchased music from the iTunes Store were copy protected with Apple's FairPlay digital rights management (DRM) system which allows protected songs to be played on up to five computers at one time, as well as unlimited devices (iPod, AppleTV, etc.) DRM protected songs cannot be played on computers not authorized to the purchaser's iTunes account. At the 2009 Macworld Conference & Expo, it was announced that the iTunes Music Store would be DRM-free, with all songs DRM-free by April 2009. 
Apple also announced changes in their price tier. They announced that songs will now cost $0.69, $0.99, or $1.29, but did not elaborate on how they will be priced. Observers expected new hits to be $1.29 while older songs will be the cheaper $0.99 or $0.69 tier.  However, many record labels have listed whole catalogs by artists with nothing but $1.29 songs, taking advantage of the price option. Due to this, there are very few songs in the iTunes store with a $0.69 price tag. 
On January 6, 2009, Phil Schiller announced in his Macworld 2009 keynote speech that over 6 billion songs had been downloaded since the service launched on April 28, 2003,  making it the largest online music store in the world.
At the previous Macworld Expo 2008, Apple CEO Steve Jobs stated that the service had set a new single day record of 20 million songs on December 25, 2007. He also announced that the iTunes Store will offer over 1,000 movies for rental by the end of February.  The iTunes movie catalog includes content from 20th Century Fox, Warner Bros., Walt Disney Pictures, Paramount Pictures, Universal Studios, and Sony Pictures Entertainment. These movies will also be transferable to all 6th generation iPods. 
On February 25, 2010, Apple announced that over 10 billion tracks had been downloaded from the iTunes Store. 
As of Tuesday, November 16, 2010, Beatles fans could download their entire catalog digitally via iTunes.  Artists whose music remains largely unavailable include Garth Brooks, Tool, and Aaliyah. The KLF, who infamously deleted their back catalogue, had their catalogue unofficially released onto the iTunes store.  
On May 30, 2007, Apple announced the launch of "iTunes U" via its digital content store, iTunes, which delivers university lectures through a format called iTunesU.   The service was created to manage, distribute, and control access to educational audio and video content for students in a college or university. Member institutions have the opportunity to have their own iTunes U site, which facilitates searching for material. The online service is free for uploading or downloading these documents. iTunes U includes lectures, language lessons, lab demonstrations, sports, and campus tours provided by many colleges and universities in the United States, United Kingdom, Australia, Canada, Ireland and New Zealand.
Right around the end of 2009/start of 2011, new members' institutions no longer have the capability to upload content to Apple's servers. Any member institutions before that are grandfathered in.
iTunes U has collected materials from a variety of locations around the world, including colleges, universities, museums, libraries and other cultural institutions of educational value. There are more than 75,000 files available for download. The Open University in the UK set the record for the most downloads as of October 3, 2011, having reached 40 million downloads. 
In late February 2013, iTunes U surpassed one billion downloads from more than 800 institutions. 
In version 12.7, iTunes iTunes U collections became a part of the Apple Podcasts family.
iTunes in the Cloud and iTunes Match
While iTunes 10 supported the Cloud, it did not integrate offline and cloud libraries. A list of previously purchased content was accessible via the iTunes store, where users could download content to the device they were using. Automatic downloading of newly purchased content could also be enabled, and iTunes Match allowed content purchased outside of the iTunes store to be uploaded to the Cloud. With the release of iTunes 11, the Cloud became fully integrated into iTunes. Content stored in a user's Cloud is displayed in the same way as that stored on their device, and online content does not have to be downloaded to be played. Films and TV shows also resume from where they were left off on the last device to have played them.
When iTunes was released, it came with support for the Kerbango Internet radio tuner service, giving users a selection of some of the more popular online radio streams available.  When Kerbango went out of business in 2001, Apple created its own Internet radio service for use with iTunes 2.0 and later.  As of February 2008, the iTunes radio service features 1795 "radio stations", mostly in MP3 streaming format. Programming covers many genres of music and talk, including streams from both internet-only sources and traditional radio stations. iTunes also supports the .pls and .m3u stream file formats used by Winamp and other media players.
Since the release of iTunes 7, Apple no longer promotes the Internet radio feature, though it remains in the application. Some third parties offer iTunes plugins that add additional radio stations.
In addition, users are able to enter additional stream feeds to listen to in their own music libraries. This is done by selecting the menu item "Advanced" > "Open Audio Stream..." or by the hotkey Ctrl-U (PC) or Command-U (Mac).
At Apple Worldwide Developers Conference (WWDC) 2013, Apple announced iTunes Radio, geared to be an obvious competitor to preexisting streaming/radio services such as Pandora Radio, Spotify, Slacker Radio, and several others. iTunes Radio is integrated with iOS 7 and 8 and iTunes 11.1 and 12. iTunes Match customers are opted-in to the full service (ad-free) whereas new/free users will have to listen through the ad-supported version. At WWDC 2015, Apple announced Apple Music, a streaming service similar to Spotify Premium, which launched on June 30 and coexists with iTunes Radio in iOS 8.4 and iTunes 12.2. iTunes Radio was discontinued on January 28, 2016, for users who were not members of Apple Music. 
Beginning with the introduction of the original iPhone, iTunes can activate an iPhone through their mobile carrier. The original plan for the iPhone 3G was to have the carrier authenticate it at the point of sale, either through iTunes or through the carrier's own activation interface.  However, a worldwide crash of iTunes' authentication servers on July 11, 2008, the day that the iPhone 3G was released, caused major issues. In some cases, AT&T and Apple Store employees told iPhone buyers to attempt to activate it at home.  Also affected were original iPhone users attempting to upgrade to the 2.0 firmware.   UK Apple, O2 and Carphone Warehouse stores were further impacted, as carrier O2's contract processing servers (known as Gateway) could not handle the number of new contracts and upgrades happening on launch day. Some stores reverted to hand written contracts, while others held stock. With the launch of the iPhone 3GS on June 19, 2009, iTunes at home activation was available for people purchasing their iPhone from AT&T Mobility and Apple. This allowed them to activate their new iPhone 3G/iPhone 3GS at home when they arrived. 
Apple revealed a new feature within iTunes 10 on September 1, 2010, called Ping,  which was intended to bring a social music networking component to users of iTunes. It was not made available to all countries.  Ping could be connected to user's Twitter accounts.  Ping connected user accounts of iTunes, allowing iTunes users to share and recommend music to one another.
Ping also allowed users to follow artists in order to see the photos and videos they have posted, their tour date, playlists they have created, and their comments on other artists’ albums. Users could create a profile so their friends could see whom they were following, what they were listening to, and what concerts they were going to. Ping also showed users' top 10 lists of songs and albums among the people they followed. It also provided artist recommendations to follow based on one's library and preference options. 
iTunes 2 was the first version of the software to be able to sync with an iPod. iTunes can automatically synchronize its music and video library with an iPod or iPhone every time it is connected. New songs and playlists are automatically copied to the iPod, and songs and playlists that have been deleted from the library on the host computer are also deleted from the iPod. Ratings awarded to songs on the iPod will sync back to the iTunes library and audiobooks will also remember the current playback position.
Automatic synchronization can be turned off in favor of manually copying individual songs or complete playlists. iTunes supports copying music to an iPod; however, only music and videos purchased from the iTunes Store can be transferred from the iPod back to iTunes. This functionality was added after third-party software was written which allowed users to copy all content back to their computer. It is also possible to copy from the iPod using ordinary Unix command line tools, or by enabling hidden file viewing in Windows Explorer, then copying music from the iPod drive to a local disk for backup. Doing this can be confusing because the files are arranged in such a way that their folders and (depending on iPod and iTunes versions) file names are seemingly picked at random as they are put on the iPod. It is worth noting, however, that the files (along with their embedded title and artist information) remain unchanged. It is therefore less confusing to let iTunes reimport, reorganize, and rename all of the files after they are backed up.
When music or video purchased through the iTunes Store is copied from an iPod, it will only play on computers that are authorized with the account that was used to purchase them. Several third party utilities can remove this limitation by stripping iTunes DRM from protected files. The legality of using such software in the United States is the subject of active debate. 
When an iPod is connected that does not contain enough free space to sync the entire iTunes music library, a playlist will be created and given a name matching that of the connected iPod. This playlist can then be modified to the user's preference in song selection to fill the available space.
The macOS version of iTunes can also synchronize with a small number of discontinued digital music players,  while the Windows version supports only the iPod.  The synchronization is limited, however, in that the iPod is the only digital music player compatible with Apple's proprietary FairPlay digital rights management technology, and thus most music purchased through the iTunes Store (before the introduction of iTunes Plus) can only be played on an iPod. The remaining ability to synchronize with a limited number of legacy digital music players is likely a remnant of Apple's history in the music industry: iTunes was released in January 2001, nine months prior to the iPod's unveiling, and slightly more than two years before the introduction of the iTunes Music Store. When iTunes was released, compatibility with other music players was critical. Since iPod has now become the dominant digital music player, Apple no longer considers that compatibility to be a necessity.
In June 2009, Palm Inc released the Palm Pre, which has the ability to sync with both the Windows and Mac OS X version of iTunes by identifying itself to iTunes as an iPod. The Pre is able to sync only DRM-free music.  However, on July 14, 2009, Apple released iTunes version 8.2.1, which prevented the Palm Pre from syncing directly with iTunes. Then on July 23, 2009, Palm Inc released WebOS 1.1, re-enabling syncing between iTunes 8.2.1 and the Palm Pre.  But Apple again prevented Palm Pre syncing with the release of iTunes 9. 
A number of unsupported third-party applications have been created to assist synchronization of songs with any music player that can be mounted as an external drive. Though iTunes is the only official method for synchronizing with the iPod, there are other applications available that allow the iPod to sync with other software players.
As of iTunes 7, purchased music can be copied from the iPod onto the computer. The computer must be authorized by that iTunes account. iTunes allows up to 5 computers to be authorized on one account. To de-authorize and register new computers thereafter, all accounts must be deleted, followed by registering the live one. This can be done only once a year.
iTunes does not feature any transfer facility for importing music files between computers directly. This is being addressed in September 2011 by iCloud, but only tracks that Apple sell in their iTunes Store are available (in 256 kbit/s AAC format) without uploading them to iCloud first. Any other tracks, that are either not available in the Store or that the user wants in different encoding can be uploaded to the iCloud with 5 GB of free space and the, as yet undisclosed, potential to purchase more storage. Though what audio formats will be accepted for upload has not been confirmed.
iTunes managed content can also be accessed via the Apple TV set-top box. Files in the iTunes library can either be synchronized with the Apple TV unit, which results in their being copied to the Apple TV's hard drive (for the first generation Apple TV), or streamed to the Apple TV directly from a Macintosh or PC. Apple TV does not require the use of iTunes (as of the 'Take Two' software update) and can now import files from the iTunes Store directly over the internet. 
In macOS, applications can access the iTunes Library directly, allowing access to its playlists and songs. Music files from iTunes can be embedded directly into Pages documents and can be used as soundtracks for iDVD, iMovie, and Keynote productions. In addition, any song exported from GarageBand, Apple's basic music-making application, is automatically added to the user's iTunes music library. iTunes Artwork.saver is a screen saver included in macOS that displays album artwork as a screen saver.
On Windows, Adobe Photoshop Elements can connect to iTunes in order to stream its photo library on Apple TV.
iTunes can be scripted, using AppleScript for macOS or using the Apple-provided SDK for iTunes on Windows, allowing many other applications to integrate themselves into iTunes. A common use is to manipulate tags, by finding and replacing text, adding text to the beginning or end of a tag, correct capitalization and more.
iTunes also supports visualizer plugins and device plugins, which allow developers to create music-driven visual displays. Free software development kits are available for Mac and Windows can be downloaded from Apple.  Device plugins allow support for additional music player devices, but the APIs are only licensed to authentic OEMs who sign a non-disclosure agreement.
Apple Inc. also offers a free iOS application, Remote, that allows the user to remotely control their iTunes library or Apple TV over DACP.  This can be downloaded from iTunes itself or directly from one's iOS device. It is only compatible with iOS 7.0 and above.
Though iTunes itself can be installed where the user desires on Windows, ancillary applications such as Bonjour, which are part of the iTunes installation, cannot be placed in a user-desired directory. 
Apple licensed G-Force for use in iTunes in 2001, and again in 2003.  This included many different WaveShapes, ColorMaps, and FlowFields; however, these configs may not be available in some versions of G-Force, although they can be found by downloading various zip files.  With iTunes 8.0 and later, which introduced a new visualizer, the option to select the iTunes Classic Visualizer is available in the Visualizer menu, and remains available in later versions of iTunes. 
The revised policy states that Apple has the right to share this information with 3rd parties who provide services to the customer, including advertising and promotion services. Apple also states that "it may be necessary" to provide this [real-time] information in response to "requests from public and governmental authorities within or outside your country of residence or if [Apple] determines that for purposes of national security, law enforcement, or other issues of public importance, disclosure is necessary or appropriate.... Additionally, in the event of a reorganization, merger, or sale we may transfer any and all personal information we collect to the relevant third party."
The revised policy does not make any distinction between warrant-based and warrantless searches, nor provide what criteria would trigger the sharing of personal real-time information with government entities, nor allow an opt-out for the location-based information.
The revised policy prompted the co-chairs of the Bi-Partisan Privacy Caucus of the United States House of Representatives to request that Apple respond to nine basic privacy questions out of concern of possible violation of that country's Federal Communications Act. The Caucus stated it was pleased with Apple's prompt written explanations, and stated they would continue to monitor the issue.  
Some products are not available in all markets. For example, an iTunes subscriber in the Republic of Ireland cannot purchase a TV programme available in the United Kingdom, despite there being no alternative provider in the Irish market.
The Telegraph reported in November 2011 that Apple had been aware of a security flaw since 2008, that would let unauthorized third parties install "updates" to end-user's iTunes' software.  They reported that security writer Brian Krebs had informed Apple of the vulnerability in 2008. They reported that the flaw was only closed in November 2011. They reported that United Kingdom security software firm Gamma International developed a program named FinFisher, intended to covertly spy on computer users, which can be clandestinely installed via bogus updates to iTunes' software. Der Spiegel reported Gamma International had advertised the capability to clandestinely install FinFisher by exploiting this iTunes vulnerability. 
iTunes has been accused of being bloated as part of its efforts to turn it from a program that plays media to an e-commerce and advertising platform,   with former PC World editor Ed Bott accusing the company of hypocrisy in its advertising attacks on Windows for similar practices.  However, other commentators contest that criticism, saying that iTunes isn't bloated, it is just feature-rich. 
The following is for the newest version of iTunes.
- Mac computer with an Intel Core Processor (Version 10.6.3 and earlier will run on PowerPC Processors)
- Intel Core 2 Duo 2.0 GHz or faster processor is required to play Standard Definition video from the iTunes Store
- 2.0 GHz Intel Core 2 Duo is required to play HD video, an iTunes LP, or iTunes Extras from the iTunes Store
- 512 MB of RAM; 1 GB is required to play HD video, an iTunes LP, or iTunes Extras
- Screen resolution of 1024×768 or greater; 1280×800 or greater is required to play an iTunes LP or iTunes Extras
- Playing videos also requires at least 16 MB of video RAM
- Broadband Internet connection to use the iTunes Store
- Apple combo drive or SuperDrive to create audio, MP3, or back-up CDs; some non-Apple CD-RW recorders may also work.
- Apple SuperDrive to back up library to DVDs; some non-Apple DVD-RW drives may also work.
- A PC with a 1 GHz Intel or AMD processor or Compatible CPU
- Intel Pentium D or faster processor is required to play Standard Definition video from the iTunes Store
- 2.0 GHz Intel Core 2 Duo or faster processor is required to play HD video, an iTunes LP, or iTunes Extras from the iTunes Store
- 512 MB of RAM; 1 GB is required to play HD video, an iTunes LP, or iTunes Extras
- Screen resolution of 1024×768 or greater; 1280×800 or greater is required to play an iTunes LP or iTunes Extras
- DirectX 9.0-compatible video card with 32 MB of video RAM; 64 MB recommended
- Broadband Internet connection to use the iTunes Store
- iTunes-compatible CD or DVD recorder to create audio CDs, MP3 CDs, or back-up CDs or DVDs
- 32-bit editions of Windows 7, Windows 8, Windows 8.1, or Windows 10
- 64-bit editions of Windows 7, Windows 8, Windows 8.1, or Windows 10 require the iTunes 64-bit installer (See note)
- 400 MB of available disk space
- Screen reader support requires Window-Eyes 7.1.1 or later
Note: Although iTunes will operate with Windows 10, there is an issue if Windows 7 or Windows 8.1 is updated to Windows 10.  The iPhone/iPad/iPod USB driver is disabled following the update. Often the only solution is to perform a clean install of Windows.