FLAC in the context of Digital audio player

A portable media player (PMP) or digital audio player (DAP) is a portable consumer electronics device capable of storing and playing digital media such as audio, images, and video files. Normally, they refer to small, battery-powered devices utilising flash memory or a hard disk for storing various media files. MP3 players has been a popular alternative name used for such devices, even if they also support other file formats and media types other than MP3 (for example AAC, FLAC, WMA).

Generally speaking, PMPs are equipped with a 3.5 mm headphone jack which can be used for headphones or to connect to a boombox, home audio system, or connect to car audio and home stereos wired or via a wireless connection such as Bluetooth, and some may include radio tuners, voice recording and other features. In contrast, analogue portable audio players play music from non-digital media that use analogue media, such as cassette tapes or vinyl records. As devices became more advanced, the PMP term was later introduced to describe players with additional capabilities such as video playback (they used to also be called "MP4 players"). The PMP term has also been used as an umbrella name to describe any portable device for multimedia, including physical formats (such as portable CD players) or handheld game consoles with such capabilities.

An audio coding format (or sometimes audio compression format) is a encoded format of digital audio, such as in digital television, digital radio and in audio and video files. Examples of audio coding formats include MP3, AAC, Vorbis, FLAC, and Opus. A specific software or hardware implementation capable of audio compression and decompression to/from a specific audio coding format is called an audio codec; an example of an audio codec is LAME, which is one of several different codecs which implements encoding and decoding audio in the MP3 audio coding format in software.

Some audio coding formats are documented by a detailed technical specification document known as an audio coding specification. Some such specifications are written and approved by standardization organizations as technical standards, and are thus known as an audio coding standard. The term "standard" is also sometimes used for de facto standards as well as formal standards.

Ogg is a digital multimedia container format designed to provide for efficient streaming and manipulation of digital multimedia. It is maintained by the Xiph.Org Foundation and is free and open, unrestricted by software patents. Its name is derived from "ogging," jargon from the computer game Netrek, alluding to the high processing cost of early versions of the software.

The Ogg container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata. In the Ogg multimedia framework, Theora provides a lossy video layer. The audio layer is most commonly provided by the music-oriented Vorbis format or its successor Opus. Lossless audio compression formats include FLAC, and OggPCM.

An anti-rival good is one where the more people share it, the more utility each person receives. It is the opposite of a rival good. Examples include software and other information goods created through the process of commons-based peer production. The term was coined by economist Steven Weber.

An anti-rival good meets the test of a public good because it is non-excludable (freely available to all) and non-rival (consumption by one person does not reduce the amount available for others). However, it has the additional quality of being created by private individuals for common benefit without being motivated by pure altruism, because the individual contributor also receives benefits from the contributions of others.

A compression artifact (or artefact) is a noticeable distortion of media (including images, audio, and video) caused by the application of lossy compression. Lossy data compression involves discarding some of the media's data so that it becomes small enough to be stored within the desired disk space or transmitted (streamed) within the available bandwidth (known as the data rate or bit rate). If the compressor cannot store enough data in the compressed version, the result is a loss of quality, or introduction of artifacts. The compression algorithm may not be intelligent enough to discriminate between distortions of little subjective importance and those objectionable to the user.

The most common digital compression artifacts are DCT blocks, caused by the discrete cosine transform (DCT) compression algorithm used in many digital media standards, such as JPEG, MP3, and MPEG video file formats. These compression artifacts appear when heavy compression is applied, and occur often in common digital media, such as DVDs, common computer file formats such as JPEG, MP3 and MPEG files, and some alternatives to the compact disc, such as Sony's MiniDisc format. Uncompressed media (such as on Laserdiscs, Audio CDs, and WAV files) or losslessly compressed media (such as FLAC or PNG) do not suffer from compression artifacts.

Ogg is a digital multimedia container file format designed to provide for efficient streaming and manipulation of digital multimedia. It is maintained by the Xiph.Org Foundation and is free and open, unrestricted by software patents. Its name is derived from "ogging," jargon from the computer game Netrek, alluding to the high processing cost of early versions of the software.

The Ogg container format can multiplex a number of independent streams for audio, video, text (such as subtitles), and metadata. In the Ogg multimedia framework, Theora provides a lossy video layer. The audio layer is most commonly provided by the music-oriented Vorbis format or its successor Opus. Lossless audio compression formats include FLAC, and OggPCM.

An audio coding format, or audio compression format, is a encoded format of digital audio, such as in digital television, digital radio and in audio and video files. Examples of audio coding formats include MP3, AAC, Vorbis, FLAC, and Opus. A specific software or hardware implementation capable of audio compression and decompression to/from a specific audio coding format is called an audio codec; an example of an audio codec is LAME, which is one of several different codecs which implements encoding and decoding audio in the MP3 audio coding format in software.

Some audio coding formats are documented by a detailed technical specification document known as an audio coding specification. Some such specifications are written and approved by standardization organizations as technical standards, and are thus known as an audio coding standard. The term "standard" is also sometimes used for de facto standards as well as formal standards.

Variable bitrate (VBR) is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate (CBR), VBR files vary the amount of output data per time segment. VBR allows a higher bitrate (and therefore more storage space) to be allocated to the more complex segments of media files while less space is allocated to less complex segments. The average of these rates can be calculated to produce an average bitrate for the file.

MP3, WMA and AAC audio files can optionally be encoded in VBR, while Opus and Vorbis are encoded in VBR by default. Variable bit rate encoding is also commonly used on MPEG-2 video, MPEG-4 Part 2 video (Xvid, DivX, etc.), MPEG-4 Part 10/H.264 video, Theora, Dirac and other video compression formats. Additionally, variable rate encoding is inherent in lossless compression schemes such as FLAC and Apple Lossless.