To create and distribute content for playback on iPod, iPhone, iPad, and in iTunes, you need to get the content (primarily audio or video) into compatible file formats. Understanding file formats and how they compare with each other can help you decide the best way to prepare your content.
Apple recommends using the following file formats:
AAC (Advanced Audio Coding) for audio content. AAC is a state-of-the-art, open (not proprietary) format. It is the audio format of choice for Internet, wireless, and digital broadcast arenas. AAC provides audio encoding that compresses much more efficiently than older formats, yet delivers quality rivaling that of uncompressed CD audio.
H.264 for video content. H.264 uses the latest innovations in video compression technology to provide incredible video quality from the smallest amount of video data. This means you see crisp, clear video in much smaller files, saving you bandwidth and storage costs over previous generations of video codecs.
One of the factors to keep in mind when preparing your content is file size. Using high-quality compressed formats, such as AAC and H.264, allows files to download faster and take up less space on a hard disk.
iPod and iTunes support many other formats, including MP3, MP3 VBR, AIFF, Apple Lossless, WAV, AA, MPEG-4, and PDF (iTunes only). iTunes U does not support the downloading of WAV or AIFF file formats on the iPod, iPhone, or iPad.
The following tables summarize the file formats that are available and list when and why you might choose one over another.
Audio File Format
AAC (Advanced Audio Coding)
A state-of-the-art, open audio file format. At any given bit rate, AAC delivers higher quality audio than other older MP3 formats.
AAC provides almost twice the clarity of MP3 audio at the same bit rate with equal or smaller file sizes.
File size: Usually less than 1 MB for each minute of content.
Use when you want CD quality audio in a highly compressed file.
AAC is the next generation in audio formats that offers:
A compressed audio format. Because it is an older format, quality is not as high as with newer formats.
File size: About 1 MB for each minute of content.
Offers good quality audio, but compression and quality are not as good as next generation formats.
MP3 VBR (Variable Bit Rate)
An enhanced MP3 format that compresses the audio at varying rates based on the content. The compression is determined moment by moment; for example, silence and simple sounds compress much more than complex sounds such as reverberation.
Unless the entire audio composition is complex, MP3 VBR provides better overall sound quality than MP3 without making the file size too large.
Video File Format
The next generation video compression technology in the MPEG-4 standard.
The result is crisp, clear video in much smaller files, saving in bandwidth costs over previous generations of video formats. For example, H.264 delivers up to four times the resolution of MPEG-4 at the same data rate.
Use when you want very high quality across the broadest range of bandwidths from 3G mobile devices to iChat AV for videoconferencing.
Because H.264 is an integral part of the QuickTime architecture in Mac OS X v10.5 Leopard, QuickTime-based applications—including iChat AV, Final Cut Pro, and other third-party applications—can take full advantage of this new video format.
Defined by MPEG (Moving Picture Experts Group) to deliver DVD-quality video at lower data rates and smaller file sizes than MPEG-2. (MPEG-2 was defined for DVD video; MPEG-4 was defined for Internet delivery of digital media.)
Based on the QuickTime architecture.
Use to create content in a simple, cost-effective “author once, play anywhere” model. You don’t have to manage the same content in multiple formats.
Works with a wide variety of devices, including mobile phones and digital still cameras.
PDF stands for Portable Document Format.
Used for text-based books or articles. PDF extension is required.
Note: iTunes and iTunes U do not write metadata to PDF files.
iPod does not support WMA, MPEG Layer 1, or MPEG Layer 2 audio files, or audible.com format 1.
To use specific artwork for individual tracks within a video, use QuickTime Pro to set the video’s poster frame. A poster frame is a still image from a video that represents the video. The default poster frame is the first frame in the video. iTunes U displays the track artwork in places such as track links and the Get Info Summary pane upon download.
© 2011 Apple Inc. All Rights Reserved. (Last updated: 2011-11-03)