iPod Software
The iPod can play MP3, AAC/M4A, Protected AAC, AIFF, WAV, Audible audiobook, and Apple Lossless audio file formats. The fifth generation iPod can also play MPEG-4 (H.264/MPEG-4 AVC), .mp4 and QuickTime video formats, with restrictions on video dimensions, encoding techniques and data-rates. Unlike most other media players, Apple does not support Microsoft's WMA audio format — but a converter for non-DRM WMA files is provided with the Windows version of iTunes. MIDI files cannot be played, but can be converted to audio files using the "Advanced" menu on iTunes. Alternative open-source audio formats such as Ogg Vorbis and FLAC are not supported.
Each time an iPod connects to its host computer, iTunes can synchronize entire music libraries or music playlists and the user can choose for automatic or manual synchronization. Song ratings can be set on the iPod and synchronized later to the iTunes library. If songs were added to the iPod on other computers, however, they won't be copied back to the music library.
iTunes Store
The iTunes Store (formerly iTunes Music Store) is an online media store run by Apple and accessed via iTunes. It was introduced on 29 April 2003 and it sells individual songs relatively easily and cheaply, with typical prices being US$0.99, EU€0.99, or GB£0.79 per song. iPods are the only portable music players that can play the purchased music. The store became the market leader soon after its launch[verification needed] and Apple announced the sale of videos through the store on 12 October 2005. Full-length movies became available on 12 September 2006.
Purchased audio files use the AAC format with added encryption. The encryption is based on the controversial FairPlay digital rights management (DRM) system. Up to five authorized computers and an unlimited number of iPods can play the files. Burning the files onto an audio CD removes the DRM, at a cost of reduced quality when re-compressed from a lossy format to the standard CDDA (CD audio) format.
iPods cannot play music files from other competing music stores such as Napster or MSN Music which use rival DRM technologies like Microsoft's protected WMA or RealNetworks' Helix DRM. RealNetworks claims that Apple is creating problems for itself, by using FairPlay to lock users into using the iTunes Store. Steve Jobs stated that Apple makes little profit from song sales, but Apple uses the store to promote iPod sales.
File storage
All iPods can function as mass storage devices to store data files. If the iPod is formatted on a Mac OS X computer it uses the HFS Plus file system format. If it is formatted on Windows, the FAT32 format is used because Windows cannot access HFS filesystems. Unlike UMS/MTP-capable digital audio players, simply copying files to the drive will not allow the iPod to properly access them (although some third party iPod software allows this). Instead, the user must use iTunes or a compatible third-party software to load audio, videos, and photos in such a way that they are playable and viewable on the iPod.
An iPod formatted as HFS Plus is able to serve as a boot disk for a Mac computer, allowing one to have a portable operating system installed. The older iPods with FireWire ports could additionally function in FireWire Disk Mode. With the advent of the Windows-compatible iPod, the iPod's default file system switched from HFS Plus to FAT32, although they can be reformatted to either filesystem (excluding the iPod shuffle which is strictly FAT32).
iTunes cannot transfer songs or videos from device to computer (although iTunes 7 allows it for music purchased online). The media files are stored on the iPod in a hidden folder, together with a proprietary database file. However, the hidden content can be accessed on the host operating system by enabling hidden files to be shown. The audio can then be recovered manually by dragging the files or folders onto the iTunes Library or by using third-party software.
In earlier iTunes versions, files were copied into these hidden folders using their original filenames. In later versions of iTunes, files were copied using random four-character filenames (such as ABCD.mp3) to make it more difficult to simply search for files and drag them out of the hidden folders. This can be worked around by either using an application that can read the tags from the files directly and display and copy them along with the filenames, or by using third-party software that is able to read the iPod database format, since the iPod's database links the randomly-named files to their titles, artists, and other information.
Additional features
The larger models also have limited PDA-like functionality and can display text files. Contacts and schedules can be viewed and synchronized with the host computer, and some built-in games are available including Brick, Parachute, Solitaire and Music Quiz. Brick (which is a clone of Breakout) was originally invented by Apple co-founder Steve Wozniak in the 1970s.
A firmware update released in September 2006 brought several new features to 5th generation iPods including downloadable games, adjustable screen brightness, and gapless playback.
Open-source alternatives
The iPodLinux project has a port of an ARM version of the Linux kernel alongside an interface called "Podzilla" that runs on all iPods, although only the first, second and third generations are officially supported by the developers. The iPod shuffle is not supported and the September 2006 iPods are incompatible.
An open-source firmware called Rockbox allows the iPod nano, mini, and all display-capable iPods after the third generation (except for the updated video iPods) to play Ogg Vorbis, FLAC, Musepack, WavPack, Shorten, and MIDI files, but not FairPlay-encrypted files. Rockbox also offers gapless playback and a more sophisticated equalizer but is in a testing stage as of September 2006.
There are also several open source alternatives to iTunes. gtkpod allows machines running virtually any OS to connect to the iPod. ephPod is another Windows iTunes alternative. MediaChest is a Java application which allows users to synchronize the iPod from different operating systems. There are also iPod plug-ins for popular music players.
There are several closed source and commercial iPod content synchronizers.
