8. About Music and Video Formats  See Also
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 Convert Audio Files to Other Formats
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No matter how easy to use a piece of software is, there are some trivialities of computer technology that you just can't escape. One of these bits of esoterica is the plethora of digital music and video file formats that you'll encounter while using iTunes. Ideally, and for the most common paths of use, file formats are little more than a curiosity you never have to deal with yourself; but the moment you try to do anything at all advanced with your music, you'll find yourself surrounded by what seems an alphabet soup of acronyms and labels, lurking malevolently just under iTunes' polished surface. It pays to know what each of these formats is all about and how to deal effectively with it. Here you'll learn what the different formats that iTunes recognizes are used for, andmore importantlyhow they relate to the different styles of music and video entertainment that iTunes helps you to collect. Music File Formats All digital music files follow essentially the same idea: a series of numbers that describe the pitch and intensity of the sound waveform at each particular instant in the audio stream, all adding up to a familiar musical sound when it's interpreted by software such as iTunes at normal playback speed. Different kinds of files differ, though, in exactly what form those numbers take. Some music formats support compression (the ability to reduce the file size by discarding relatively unimportant sound information, or by indexing small repeated fragments of sound instead of encoding all of them directlyin addition to other, ingeniously mathematical methods). Some formats support Digital Rights Management (DRM), enforcing copy protection. Some forms of digital audio files encode stereo data differently from others, resulting in a somewhat different sound quality. These subtle but important differences are what make some formats more suitable for certain tasks than others, and explain why we have to deal with so many different file formats in the world of digital music. Key Terms Format The specific internal data structure of a digital music or video file, determined by the software that first popularized a given type of file. Competing software has often resulted in different incompatible formats for similar kinds of files. Compression Fitting more music into a fewer number of bytes by discarding unimportant musical data or indexing repeated patterns.
The following audio file formats are either supported directly by iTunes or destined to be a part of your life as you work with iTunes. Except where noted, the customary filename extensionthe three or four letters after the final period (.) in a file's nameis the same as the acronym of the format listed. CDDA (Compact Disc Digital Audio) An uncompressed, true stereo digital audio stream made up of a simple series of audio samples. This is the standard format in which every commercial audio CD is encoded and the format in which iTunes burns audio CDs. The CDDA format is essentially interchangeable with AIFF and WAV formats, and it's almost never used directly on computers. AIFF (Audio Interchange File Format) An uncompressed audio stream format developed by Apple and popularized as the default sound format of the Macintosh platform. It is still the preferred format for raw audio editing on the Mac. You can convert AIFF files without loss of quality to WAV format and back. WAV (Windows WAVeform file) An uncompressed audio stream format developed by Microsoft and IBM. Equivalent to AIFF in its supported features and file size, WAV is the default raw audio format for Windows. You can convert WAV files without loss of quality to AIFF format and back. MP3 (MPEG-1 Audio Layer 3) Developed in the early 1990s as part of the MPEG video/audio compression specification, MP3 is the first audio format to have brought the file size of individual song tracks down to the point where they could be easily transferred across the Internet while still sounding nearly true to the original CD-quality sound from which they were derived. Encoding technology for MP3 files is subject to patents held by Thomson Consumer Electronics and the Fraunhofer Institute, which contributed to the format's original design. MP3 is a lossy compression format, meaning that any music converted to MP3 format cannot be flawlessly converted back to its original format; some music data is inevitably lost. The benefit is that an MP3 file usually achieves about a 12:1 compression ratio over the uncompressed source, depending on the bit rate you select during encoding.
Key Terms Lossy A compression or conversion process in which some sound information or resolution is irretrievably lost, as when encoding a CD to MP3 format. The converse is lossless compression, meaning a reversible process in which no information is lost. Lossless A compression or conversion process that preserves perfect sound quality from the original source. Lossless compression doesn't achieve such small file sizes as lossy compression, but it's reversible. Bit rate The number of bits per second consumed by an audio stream. The bit rate can be constant or variable. If the rate is constant, you can use it to calculate how much disk space a song file will take up.
MP3's compression is achieved through a number of techniques, including the discarding of superfluous (inaudible) audio data and the application of psychoacoustics. Stereo information is usually done in "joint stereo" mode. That means that instead of two separate tracks for the left and right channels, most information is recorded as a "mono" track and a separate channel records the separation from left to right, which saves on file size. Also, Variable Bit Rate (VBR) encoding is frequently employed to encode lower-complexity sections of music at a lower bit rate, saving space without sacrificing audio quality. MP3 files have no DRM technology built in, so there is no way for a copyright holder to control or track the spread of an MP3 version of a song. MP3 files do, however, have info tagsalso known as ID3 tagsthat allow the user to embed a wide variety of organizational information into the file's text headers. This information does not interfere with the audio stream, but it gives software such as iTunes the ability to organize MP3 files with much better control and flexibility than with filenames alone. In iTunes, an MP3 file is identified in the Kind column as MPEG audio file. AAC (Advanced Audio Coding) The official successor to MP3, AAC (another lossy compression format) is the latest iteration of the audio specification in the MPEG standard, part of the MPEG-4 framework that underlies modern versions of QuickTime. Apple is currently the most visible company using AAC in its products, although it is far from being a "proprietary" format; the only thing proprietary about AAC as used in the iTunes Music Store is the way the DRM scheme (known as FairPlay) is keyed to individual purchasers. Functionally, however, as far as any company that wants to interoperate with music purchased through iTunes, Apple's format is essentially closed.  AAC files incorporate many advances over the earlier MP3 format, including as many as 48 distinct audio channels, a more dynamic form of stereo encoding, and a notably smaller file size for files that are encoded with the same subjective sound quality. This means that if you encode your CD collection in AAC format instead of MP3, you can save about 25 percent of your disk space (which, remember, also applies to the space available on your iPod). AAC supports all the same info tags that MP3 does.
There are two flavors of AAC as used in iTunes: protected and unprotected. Protected AAC files are keyed to an individual purchaser's identity and cannot be opened on a given computer unless that computer has been authorized with the central iTunes authorization servers; as many as five separate computers can be authorized at one time for a single purchaser account. (See  Authorize a Computer to Play Purchased Music for more information.) Unprotected AAC files are as freely portable and playable as MP3 files are; you can send an unprotected AAC file to anyone else with iTunes or any other software capable of reading AAC files, and the recipient can play it successfully. When you import music from your CD collection, iTunes creates the digital music files by default in unprotected AAC format. AAC files are identified by either an .m4a (MPEG-4 Audio) or .m4p (MPEG-4 Protected) filename extension, depending on whether the files are protected with DRM. WMA (Windows Media Audio) Microsoft's answer to MP3 (and later, to AAC as used in iTunes), WMA is a lossy compression format that is entirely proprietary and owned by Microsoft. Its capabilities are comparable to those of AACthe audio quality for a given file size is considerably better than with MP3, and thus for the same audio quality you get significant file size savings. WMA also comes in both protected and unprotected flavors. iTunes for Windows can import unprotected WMA files by converting them to AAC on-the-fly. The DRM scheme in WMA files as sold through the online music stores that compete with the iTunes Music Store is flexible and is implemented differently by various sellers. Some stores restrict copying and playback to a certain number of computers, like iTunes does. Others, like Napster's subscription service, enforce an expiration date beyond which you cannot open a file; periodic authorization is required to extend the expiration date on these files. Still other services set a limit on the number of times you can play a given song before it becomes locked. Apple Lossless A format developed by Apple and released with iTunes 4.5 in April 2004, with the intention of supporting high-quality audio storage for professional musicians and audiophiles without requiring the full amount of disk space required by uncompressed AIFF, WAV, or CDDA data. Apple Lossless achieves compression of about 2:1 over the uncompressed source data by using techniques similar to those found in GIF or ZIP files (both compression formats that must by their nature be totally lossless). If you encode your music using Apple Lossless, expect to consume about 5 megabytes (MB) of disk space for every minute of music; but this music will be at true CD quality without even the minimal degradation of quality found in MP3 or AAC formats. Apple Lossless files are encapsulated in MPEG-4 wrappers; thus, they have an .m4a filename extension. These files are not, however, AAC files. MIDI (Musical Instrument Digital Interface) Completely unlike all the preceding formats, MIDI is not a series of samples at all, but a synthesized music format. MIDI files are generally tiny compared to sampled music files such as AAC and MP3only 20 to 50 kilobytes (KB)because all they contain are lists of commands comparable to what you would see on a piece of sheet music. MIDI files depend on a library of playback technology to interpret these commands, as an orchestra would read the sheet music in front of it; both Windows and Mac OS X can play MIDI files natively, but the playback quality of a MIDI file depends greatly on the quality of the synthesized instruments in the software you use. iTunes can add MIDI files to its Library and play them using the QuickTime MIDI instruments, but you cannot transfer these files to the iPod. MIDI files generally have a .mid extension.
iTunes lets you convert between most of these formats, if not bidirectionally, at least from each to a native format such as AAC or MP3. In the tasks in this chapter, you will see how to take advantage of the strengths of these different formats as you bring in your music from varying sources to consolidate it into your digital iTunes Library. Video File Formats Video files have their own set of formats, each defined by the company or software that originally popularized it. Some video formats are just frameworks that can support many different codecs (encoding and decoding algorithms); others are more monolithic in nature, with the format and the codec being synonymous. What you have to know is that iTunes works with all the video formats supported by Apple's QuickTime multimedia architecture, but the iPod supports a much more limited range of file formats. MPEG Developed by the Moving Picture Experts Group in the early 1990s, MPEG (whose files end in .mpg or .mpeg) is a format that's widely supported on all computing platforms, including QuickTime and iTunes. The original MPEG standard (MPEG-1) contains the specification for MP3 audio files, as described earlier. The audio and video tracks in an MPEG file are multiplexed or "muxed," meaning that they're tied together and cannot be independently edited. In iTunes, an MPEG file is listed in the Kind column as QuickTime movie file. Because MPEG's compression technology is not particularly advanced (and thus its quality-for-file-size compromise is not ideal), MPEG files are not supported on the iPod; however, iTunes can convert them to an iPod-compatible format. (See  Put Your Home Movies and Downloaded Videos on Your iPod.) AVI The Microsoft multimedia container format, Audio/Video Interleave is a framework developed in 1992 that supports a wide variety of different codecs. The most popular video format on the Internet today (used for distributing illicit recordings of movies and TV shows, in the same way that MP3 files became the preferred format for digital music piracy) is AVI with the DiVX codec or one of its relatives. Even though QuickTime can play AVI files as long as it recognizes the codec, you cannot import AVI files into iTunes or transfer them to the iPod. Flash Popularized in the late 1990s by Macromedia (now Adobe), Flash is very different from the other types of video files listed here. It's a sprite animation framework that uses vector images described by mathematical curves. This approach results in quite small file sizes even for long-running videos; thus, Flash has become very popular for distributing movies over the Internet. However, Flash files (with an .swf) extension) are supported only to a limited extent by QuickTime and cannot be added to iTunes or transferred to the iPod. Windows Media A comparatively recent development by Microsoft, Windows Media Video (.wmv) files are a proprietary standard being popularized by the movie-making tools that are built into Windows, and they are one of the more common video formats on the Internet today. (WMV is the video counterpart to WMA.) Windows users can play WMV files natively in Windows Media Player; Mac users can play them in the QuickTime player using a free plug-in from Flip4Mac and Microsoft (http://flip4mac.com/); this plug-in also allows Mac users to import WMV files into iTunes. However, you cannot transfer these WMV files to the iPod, and because a plug-in to add WMV support to QuickTime is not available for Windows, you can't add WMV files to iTunes in Windows. QuickTime Apple's own venerable video framework, QuickTime files work like AVI files in that they can use any of a myriad of different codecs, including very modern ones such as MPEG-4. The .mov extension can be confusing; it indicates a QuickTime wrapper on a movie file that can be self-contained or just consist of a pointer to another file or set of files on your disk or on the Internet. Most .mov files that you find on the Internet are in a popular codec such as Sorenson 3 or MPEG-4/AVC (H.264) and can be used in iTunes with no trouble. However, you have to convert some QuickTime files to a compatible format (see Put Your Home Movies and Downloaded Videos on Your iPod) before you can transfer them to the iPod. MPEG-4 The newest iteration of the MPEG standard is the native and preferred format for both iTunes and the iPod. It's also the foundation for the modern QuickTime architecture. MPEG-4 files can contain any of several different codecs, but the most efficient one (and the one used by iTunes and the iTunes Music Store) is H.264, also known as AVC (Advanced Video Coding), which enables videos to display a broadcast-quality picture at a file size that is suitable for downloading. As with AAC audio files, MPEG-4 files come in both protected and unprotected varieties, although both use the extension .m4v (MPEG-4 Video). Unprotected MPEG-4 files also use that extension. You can import any MPEG-4 video file into iTunes and transfer it to the iPod for portable viewing.
In summary, iTunes can import and play MPEG, AVI, QuickTime, and MPEG-4 files (and WMV files if you have a Mac and the Flip4Mac plug-in). To transfer movie files to the iPod, you must ensure that they are in MPEG-4 format, although iTunes can convert several kinds of files to MPEG-4 for use on the iPod. Styles of Music and Video in iTunes iTunes distinguishes between a number of different kinds of entertainment media, depending on how the media is presented and what mechanisms exist for organizing it. Following is a list of the different kinds of media you'll find in iTunes: Digital music Any music, spoken word, comedy, or other audio that you would normally expect to find on CDs. This is the bulk of what you'll collect in iTunes, and iTunes' primary goal is to make the navigation and playback of your digital music as versatile as possible. Digital music can be in MP3, AAC, AIFF, WAV, Apple Lossless, or MIDI formats (although MP3 and AAC are the most common). Digital music is organized in the Library, which is at the top of the iTunes Source pane. Podcasts A podcast can be anything from a simple downloadable MP3 file of a guy talking, to a multichapter audio stream of music, comedy, politics, and commentary with artwork displayed at each named chapter marker, or even a video stream in MPEG-4 format. Because a podcast is episodic in nature, with new episodes being released on a regular basis (often weekly), you subscribe to a podcast using the URL (Web address) of its RSS feed (see  Watch for Newly Added Music Using an RSS Feed) or by selecting it in the Podcast directory of the iTunes Music Store. iTunes then downloads new episodes when they become available, and it alerts you to episodes you haven't played yet using a blue dot that also appears next to the episode's listing on the iPod. Podcasts by default support automatic bookmarking, which means that iTunes keeps track of your place when you stop listening to the audio stream and resumes at that point when you play the podcast episode again. It even synchronizes the bookmark to the iPod so that you can go from iTunes to the iPod and have the episode always pick up right where you last left off. See  Subscribe to and Listen to Podcasts for more details.
Key Terms Bookmarking Not an official term; refers to iTunes' ability to keep track of where you left off listening to a podcast or audiobook or stopped watching a TV show; iTunes starts there again when you view the item again, whether in iTunes or on the iPod. You can enable or disable bookmarking on a per-file basis in the Options pane of the Info window, using the Remember playback position check box. Audiobook The digital equivalent of the spoken-word tape. It's a special kind of digital audio file that plays for a long time as its content (the text of a book or speech) is read. The file supports automatic bookmarking and multiple internal chapter markers, and the iPod has the ability to speed up and slow down the rate at which it is read.
Audiobooks An audiobook is the digital equivalent of a book on tape. Spoken narration of a book is recorded into a long audio file, usually in AAC format, and distributed in several parts that can each last for hours. A single audio file representing a part of the book can have its own subdivisions, or "chapters," that you can skip to using the selector that appears next to the status display in iTunes when you're playing it. Audiobooks support automatic bookmarking, making sure that you don't lose your place in a long stream of narration. The iPod, additionally, can speed up or slow down the playback speed at which the audiobook is read without affecting the pitch of the narrator's voice. Audiobooks are organized with your digital music in the iTunes Library, and they have their own listing in the Music menu on the iPod; see  Listen to an Audiobook or Podcast at Home or on the Go for more information. Internet Radio A "stream" of audio data (usually in MP3 format) coming from a source on the Internet, Internet Radio data cannot be saved directly by iTunes, paused, rewound, or scanned using the scrub barit's a live stream to which you connect by specifying a web address to listen to. Favorite Internet Radio streams are added to your iTunes Library as you listen to them so that you can return to them whenever you want, but (naturally) you cannot transfer them to your iPod. Internet Radio streams sometimes use downloaded "playlist" files to schedule the playback of tracks that are stored on the server. Refer to  Listen to an Internet Radio Station for more information. Movies This category of video files indicates standalone items such as short films from Pixar and Disney, home movies, and videos you download off the Internet, which can be in QuickTime or MPEG-4 format in iTunes, and only in MPEG-4 format on the iPod. Movies that you buy from the iTunes Music Store have automatic bookmarking turned on by default, allowing you to keep your place and return to the movie later. Other movies have to have bookmarking turned on manually to keep track of their playback positions. Music videos A specific category of videos that you can buy from the iTunes Music Store, music videos are just like the ones you would see on MTVpopular songs set to video. These files do not support automatic bookmarking by default (they're usually no longer than a typical song, so bookmarking isn't really important), but you can turn it on for individual files if you want. TV shows Released sequentially as they're broadcast new, and in complete "seasons" (analogous to "albums" for music), TV shows are episodes of popular television series from any of more than a dozen popular networks. Because they have no commercials, half-hour episodes last for about 22 minutes and hour-long episodes are 45 minutes, although some cable shows that were designed to be broadcast without commercial interruption last for the complete hour. TV shows support automatic bookmarking so you won't lose your place in iTunes or on the iPod. Booklets Presented as premiums in the iTunes Music Store, usually accompanying special packaged sets of digital music such as the $150 The Complete U2, digital booklets are computerized versions of the books you might expect to get in a premium CD or boxed music set at the record store. Containing such things as lyrics, biographies, interviews, cover art, and artist commentaries on the music it accompanies, booklets are listed in the iTunes Library along with the artists and albums to which they pertain.
These subdivisions of your audio and video files allow you to narrow your searching scope when you search for music or videos using the Search box. (See  Find and Play Music in iTunes for more information about searching.) Be sure to familiarize yourself with the subtle differences between each of these types of media, because when you want to dial up a specific podcast episode, audiobook chapter, or TV show episode on your iPod, you need to know what groupings to look for on the way to your desired content. |
