iTunes U Administration Guide: Understanding File Formats

Understanding File Formats

To create and distribute content for playback on iPod, iPhone, Apple TV, 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 will 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.

Note: iPod and iTunes support many other formats, including MP3, MP3 VBR, AIFF, Apple Lossless, WAV, AA, MPEG-4, and PDF (iTunes only).

The following tables summarize the file formats that are available and list when and why you might choose one over another.

Audio File Format	Description	Usage
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: Improved compression with higher quality results and smaller file sizes Increased quality at a wide range of data rates Support for multichannel audio, providing up to 48 full frequency channels Higher resolution audio, yielding sampling rates of up to 96 kHz Improved decoding efficiency, requiring less processing power for decoding
MP3	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.

Audio File Format

Description

Usage

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:

Improved compression with higher quality results and smaller file sizes
Increased quality at a wide range of data rates
Support for multichannel audio, providing up to 48 full frequency channels
Higher resolution audio, yielding sampling rates of up to 96 kHz
Improved decoding efficiency, requiring less processing power for decoding

MP3

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	Description	Usage
H.264	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.
MPEG-4 Video	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 booklets	PDF stands for Portable Document Format. PDF files can be stored and accessed from within iTunes and iTunes U, but not on iPod.	Used for text-based books or articles. PDF extension is required. Note: iTunes and iTunes U do not write metadata to PDF files.

Video File Format

Description

Usage

H.264

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.

MPEG-4 Video

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 booklets

PDF stands for Portable Document Format.

PDF files can be stored and accessed from within iTunes and iTunes U, but not on iPod.

Used for text-based books or articles. PDF extension is required.

Note: iTunes and iTunes U do not write metadata to PDF files.

Notes:

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.