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26-415: ALAC supports up to 8 channels of audio at 16, 20, 24 and 32 bit depth with a maximum sample rate of 384 kHz. ALAC data is frequently stored within an MP4 container with the filename extension .m4a . This extension is also used by Apple for lossy AAC audio data in an MP4 container (same container, different audio encoding). The codec can also be used by the .CAF file type container, though this

52-426: A finite number of values from some alphabet , such as letters or digits. An example is a text document , which consists of a string of alphanumeric characters . The most common form of digital data in modern information systems is binary data , which is represented by a string of binary digits (bits) each of which can have one of two values, either 0 or 1. Digital data can be contrasted with analog data , which

78-511: A general structure for time-based media files. It in turn is used as the basis for other file formats in the family (for example, MP4, 3GP , and Motion JPEG 2000 ). The MP4 file format defined some extensions over the ISO Base Media File Format to support MPEG-4 visual/audio codecs and various MPEG-4 Systems features such as object descriptors and scene descriptions. Some of these extensions are also used by other formats based on

104-473: A new one should not be invented. While the only filename extension defined by the standard is .mp4 , various filename extensions are commonly used to indicate intended content: Most kinds of data can be embedded in MPEG-4 Part 14 files through private streams . A separate hint track is used to include streaming information in the file. The registered codecs for MPEG-4 Part 12-based files are published on

130-418: A single word. This is useful when combinations of key presses are meaningful, and is sometimes used for passing the status of modifier keys on a keyboard (such as shift and control). But it does not scale to support more keys than the number of bits in a single byte or word. Devices with many switches (such as a computer keyboard ) usually arrange these switches in a scan matrix, with the individual switches on

156-543: A switch is pressed, released, and pressed again. This polling can be done by a specialized processor in the device to prevent burdening the main CPU . When a new symbol has been entered, the device typically sends an interrupt , in a specialized format, so that the CPU can read it. For devices with only a few switches (such as the buttons on a joystick ), the status of each can be encoded as bits (usually 0 for released and 1 for pressed) in

182-460: Is a digital multimedia container format most commonly used to store video and audio , but it can also be used to store other data such as subtitles and still images. Like most modern container formats , it allows streaming over the Internet . The only filename extension for MPEG-4 Part 14 files as defined by the specification is .mp4 . MPEG-4 Part 14 (formally ISO / IEC 14496-14:2003 )

208-421: Is a standard specified as a part of MPEG-4 . Portable media players are sometimes advertised as " MP4 players ", although some are simply MP3 players that also play AMV video or some other video format and do not necessarily play the MPEG-4 Part 14 format. MPEG-4 Part 14 is an instance of the more general ISO / IEC 14496-12:2004 (MPEG-4 Part 12: ISO base media file format ), which is directly based upon

234-536: Is much less common. ALAC is not a variant of AAC (which is a lossy format), but rather an unrelated lossless format that uses linear prediction (similar to other lossless codecs). ALAC also does not use any DRM scheme; but by the nature of the MP4 container , it is feasible that DRM could be applied to ALAC much in the same way it is applied to files in other QuickTime containers. According to Apple, audio files compressed with its lossless codec will use up "about half

260-500: Is not mandatory, and some invented and used code-points are not registered. When someone is creating a new specification derived from the ISO Base Media File Format, all the existing specifications should be used both as examples and as a source of definitions and technology. If an existing specification already covers how a particular media type is stored in the file format (e.g., MPEG-4 audio or video in MP4), that definition should be used, and

286-436: Is rather simpler than conversion of continuous or analog information to digital. Instead of sampling and quantization as in analog-to-digital conversion , such techniques as polling and encoding are used. A symbol input device usually consists of a group of switches that are polled at regular intervals to see which switches are switched. Data will be lost if, within a single polling interval, two switches are pressed, or

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312-577: Is represented by a value from a continuous range of real numbers . Analog data is transmitted by an analog signal , which not only takes on continuous values but can vary continuously with time, a continuous real-valued function of time. An example is the air pressure variation in a sound wave . The word digital comes from the same source as the words digit and digitus (the Latin word for finger ), as fingers are often used for counting. Mathematician George Stibitz of Bell Telephone Laboratories used

338-986: The Apache License version 2.0 on October 27, 2011. On May 17, 2021, Apple announced that they would begin offering lossless audio in Apple Music in June 2021, with all lossless music being encoded using ALAC. All current iOS devices can play ALAC encoded files. The open source library libavcodec incorporates both a decoder and an encoder for the ALAC format, which means that media players based on that library (including VLC media player and MPlayer , as well as many media center applications for home theater computers , such as Plex , Kodi , and Boxee ) are able to play ALAC files. As of 2015, Windows 10 includes support for ALAC encoding and decoding, thereby enabling other media players to use it, e.g. Windows Media Player when ripping CDs or

364-563: The QuickTime File Format , which was published in 2001. MPEG-4 Part 14 is essentially identical to the QuickTime File Format but formally specifies support for Initial Object Descriptors (IOD) and other MPEG features. MPEG-4 Part 14 revises and completely replaces Clause 13 of ISO/IEC 14496-1 (MPEG-4 Part 1: Systems), in which the file format for MPEG-4 content was previously specified. The MPEG-4 file format, version 1,

390-576: The Spotify desktop client for playback of local .m4a files. The library was subsequently optimized for ARM processors and included in Rockbox . Foobar2000 will play ALAC files as will JRiver Media Center and BitPerfect. Lossless music via ALAC was added to Apple Music in June 2021, at no additional cost for all subscribers. The maximum fidelity for lossless music on Apple Music is 24-bit at 192 kHz. MPEG-4 Part 14 MPEG-4 Part 14 , or MP4 ,

416-499: The ISO base media file format (e.g., 3GP). A list of all registered extensions for ISO Base Media File Format is published on the official registration authority website. The registration authority for code-points (identifier values) in "MP4 Family" files is Apple Inc., and it is named in Annex D (informative) in MPEG-4 Part 12. Codec designers should register the codes they invent, but registration

442-534: The Music application. The codec is also used in the AirPort and AirPlay implementation. David Hammerton and Serafina Brocious analyzed and reverse engineered the codec without any documents on the format. On March 5, 2005, Hammerton published a simple open source decoder written in the C programming language on the basis of the work. The Apple Lossless Encoder (and decoder) were released as open source software under

468-514: The file. In the latter case, the video file is not playable if the file is incomplete (truncated). MP4 files can contain metadata as defined by the format standard, and in addition, can contain Extensible Metadata Platform (XMP) metadata. Digital data Digital data , in information theory and information systems , is information represented as a string of discrete symbols, each of which can take on one of only

494-586: The format has been recommended for older iPod devices based on claims of lower power usage. Partly because of the use of an MP4 container, ALAC does not contain integrated error checking. The data compression software for encoding into ALAC files, Apple Lossless Encoder, was introduced into the Mac OS X Core Audio framework on April 28, 2004, together with the QuickTime 6.5.1 update, thus making it available in iTunes since version 4.5 and above, and its replacement,

520-408: The intersections of x and y lines. When a switch is pressed, it connects the corresponding x and y lines together. Polling (often called scanning in this case) is done by activating each x line in sequence and detecting which y lines then have a signal , thus which keys are pressed. When the keyboard processor detects that a key has changed state, it sends a signal to the CPU indicating the scan code of

546-406: The key and its new state. The symbol is then encoded or converted into a number based on the status of modifier keys and the desired character encoding . A custom encoding can be used for a specific application with no loss of data. However, using a standard encoding such as ASCII is problematic if a symbol such as 'ß' needs to be converted but is not in the standard. It is estimated that in

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572-416: The storage space" that the uncompressed data would require. Testers using a selection of music have found that compressed files are about 40% to 60% the size of the originals depending on the kind of music, which is similar to other lossless formats. ALAC has been measured to require around four times as much CPU power to decode than FLAC does, with implications for battery life on limited-power devices. Still

598-422: The website of MP4 Registration authority (mp4ra.org), but most of them are not widely supported by MP4 players. The widely supported codecs and additional data streams are (but many more are also supported, including audio like FLAC or TrueHD ): The moov atom contains information about video resolution, frame rates, orientation, display characteristics, and more. It might be placed at the beginning or end of

624-435: The word digital in reference to the fast electric pulses emitted by a device designed to aim and fire anti-aircraft guns in 1942. The term is most commonly used in computing and electronics , especially where real-world information is converted to binary numeric form as in digital audio and digital photography . Since symbols (for example, alphanumeric characters ) are not continuous, representing symbols digitally

650-470: The year 1986, less than 1% of the world's technological capacity to store information was digital and in 2007 it was already 94%. The year 2002 is assumed to be the year when humankind was able to store more information in digital than in analog format (the "beginning of the digital age "). Digital data come in these three states: data at rest , data in transit , and data in use . The confidentiality, integrity, and availability have to be managed during

676-511: Was published in 2001 as ISO/IEC 14496-1:2001, which is a revision of the MPEG-4 Part 1: Systems specification published in 1999 (ISO/IEC 14496-1:1999). In 2003, the first version of the MP4 file format was revised and replaced by MPEG-4 Part 14: MP4 file format (ISO/IEC 14496-14:2003), commonly named as MPEG-4 file format version 2. The MP4 file format was generalized into the ISO Base Media File format ISO/IEC 14496-12:2004, which defines

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