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Encyclopedia > RealAudio

RealAudio is a proprietary audio format developed by RealNetworks. It uses a variety of audio codecs, ranging from low-bitrate formats that can be used over dialup modems, to high-fidelity formats for music. It can also be used as a streaming audio format, that is played at the same time as it is downloaded. Many internet radio stations use RealAudio to stream their programming over the internet in real time. Proprietary indicates that a party, or proprietor, exercises private ownership, control or use over an item of property, usually to the exclusion of other parties. ... This article or section does not cite its references or sources. ... An audio codec is a computer program that compresses/decompresses digital audio data according to a given audio file format or streaming audio format. ... Streaming media is multimedia that is continuously received by, and normally displayed to, the end-user while it is being delivered by the provider. ... Internet radio (aka e-Radio) is an audio broadcasting service transmitted via the Internet. ...


The first version of RealAudio was released in 1995. As of 2006, the current version is RealAudio 10. 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ...

Contents

File extensions

RealAudio files were originally identified by a filename extension of .ra (for Real Audio). In 1997 RealNetworks also began offering a video format called RealVideo. The combination of the audio and video formats was called RealMedia and used the file extension .rm. However, the latest version of RealProducer, Real's flagship encoder, reverted to using .ra for audio-only files, and began using .rv for video files (with or without audio), and .rmvb for VBR video files. The .ram (Real Audio Metadata) and .smil (Synchronized Multimedia Integration Language) file formats are sometimes encountered as links from web pages (see Streaming Audio section below). A filename extension is a suffix to the name of a computer file applied to show its format. ... RealVideo is a proprietary video format developed by RealNetworks. ... RealMedia is a multimedia container format created by RealNetworks. ... Variable bit rate (VBR) is a term used in telecommunications and computing that relates to sound or video quality. ... SMIL (pronounced or smile), the Synchronized Multimedia Integration Language, is a W3C Recommended XML markup language for describing multimedia presentations. ...


Players

The official player for RealMedia content is RealNetworks' RealPlayer, currently at version 10.5, and is available for various platforms in binary form. Several features of this program have proven controversial, and many alternative players have been developed. RealNetworks initially tried to discourage development of alternative players by keeping their audio format secret. However, in recent years, RealNetworks has made efforts to be somewhat more open, and has founded the Helix Community, a collaborative open source project, to extend their media framework. RealPlayer is a cross-platform media player by RealNetworks that plays a number of multimedia formats including MP3, MPEG-4, QuickTime, Windows Media and multiple versions of proprietary RealAudio and RealVideo codecs. ... Helix is RealNetworks open source media framework. ... Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ...


When RealAudio was introduced, RealNetworks disclosed no technical details about the audio format or how it was encoded, but it was soon noticed that some of the audio codecs used in RealAudio were identical to those used in cellular telephones and digital television. As these formats had been described in detail in various technical papers and standards documents, it was possible to write software capable of playing RealAudio based on this information. Cellular redirects here. ... Digital television (DTV) is a telecommunication system for broadcasting and receiving moving pictures and sound by means of digital signals, in contrast to analog signals used by analog (traditional) TV. DTV uses digital modulation data, which is digitally compressed and requires decoding by a specially designed television set, or a...


A variety of unofficial players now exist, including MPlayer, JetAudio and Real Alternative. However, Real Alternative does not decode the audio data by itself, but relies on the dynamically linked libraries (DLLs) from the official RealPlayer. Thus Real Alternative requires RealPlayer to be installed (or at least its DLLs) in order to function. Most other players are based on ffmpeg, which has its own audio codec library. The audio codecs in ffmpeg were written based on the publicly available information about the formats, and do not use the RealPlayer or Helix software. It is also possible to obtain codecs which allow Windows Media Player to play some versions of RealAudio. This article is about the open source media player. ... JetAudio is a company established in September 2000. ... Real Alternative is a codec designed for playing RealMedia files, which normally require Real Player, with any video player. ... In computer science, a library is a collection of subprograms used to develop software. ... FFmpeg is a collection of free software that can record, convert and stream digital audio and video. ... Codec is a portmanteau of coder/decoder, which describes a device or program capable of performing transformations on a data stream or signal. ... Windows Media Player (WMP) is a digital media player and media library application developed by Microsoft that is used for playing audio, video and images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. ...


Although RealNetworks has made the Helix player available as an open source project, they have kept some of the audio codecs proprietary, and the Helix player can not play all RealAudio files.


Streaming Audio

RealAudio was developed as a streaming media format, meaning that it can be played while it is downloaded. It is possible to stream RealAudio using HTTP. In this case, the RealAudio file is retrieved similarly to a normal web page, but playback begins as soon as the first part is received and continues while the rest of the file is downloaded. Using http streaming works best with pre-recorded files. Some alternative protocols have been developed which work better for live broadcasts. Streaming media is multimedia that is continuously received by, and normally displayed to, the end-user while it is being delivered by the provider. ... HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...


The first version of RealAudio used a proprietary protocol called PNA or PNM to send streaming audio data. RealNetworks later switched to the IETF standardized Real Time Streaming Protocol (RTSP) but they use RTSP only to manage the connection. The actual audio data is sent with their own proprietary RDT protocol, which they initially kept secret. Recently some specifications for the RDT protocol have been made public through the Helix Community project. The open-source MPlayer project eventually developed a means of playing the RDT streams. The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ... The Real Time Streaming Protocol (RTSP), developed by the IETF and published in 1998 as RFC 2326, is a protocol for use in streaming media systems which allows a client to remotely control a streaming media server, issuing VCR-like commands such as play and pause, and allowing time-based... RDT (Real Data Transport) is a transport protocol developed by RealNetworks in the 1990s. ... Helix is RealNetworks open source media framework. ...


In many cases, web pages do not link directly to a RealAudio file. Instead they link to a .ram (Real Audio Metadata) or SMIL file. This is a small text file containing a link to the audio stream. When a user clicks on such a link, the user's web browser downloads the .ram or .smil file and launches the user's media player. The media player reads the pnm or rtsp URL from the file and then plays the stream. A hyperlink (often referred to as simply a link), is a reference or navigation element in a document to another section of the same document, another document, or a specified section of another document, that automatically brings the referred information to the user when the navigation element is selected by... SMIL (pronounced or smile), the Synchronized Multimedia Integration Language, is a W3C Recommended XML markup language for describing multimedia presentations. ... It has been suggested that this article or section be merged with Plain text. ... A Uniform Resource Locator, URL (spelled out as an acronym, not pronounced as earl), or Web address, is a standardized address name layout for resources (such as documents or images) on the Internet (or elsewhere). ...


With RealPlayer, it is not possible to save an audio stream to a file, but other programs, including MPlayer, VLC media player, StreamBox VCR, HiDownload and Real7ime Converter can do so. RealPlayer is a cross-platform media player by RealNetworks that plays a number of multimedia formats including MP3, MPEG-4, QuickTime, Windows Media and multiple versions of proprietary RealAudio and RealVideo codecs. ... This article is about the open source media player. ... VLC media player is a free software (GPL) media player by the VideoLAN project. ...


Codecs

RealAudio files are compressed using several different audio codecs. Each codec is identified by a four character code. Below is a list of the codecs and the version in which each was introduced: An audio codec is a computer program that compresses/decompresses digital audio data according to a given audio file format or streaming audio format. ... A FOURCC (literally, four character code) is a sequence of four bytes used to uniquely identify data formats. ...

  • lpcJ: IS-54 VSELP (RealAudio 1)
  • 28_8: G.728 LD-CELP (RealAudio 2)
  • dnet: Dolby AC3 (RealAudio 3)
  • sipr: Sipro Lab Telecom ACELP-NET (RealAudio 4/5)
  • cook: G2/Cook Codec (RealAudio 6)
  • atrc: Sony ATRAC3 (RealAudio 8)
  • raac: MPEG-4 LC-AAC (RealAudio 9)
  • racp: MPEG-4 HE-AAC (RealAudio 10)
  • ralf: RealAudio Lossless Format (RealAudio 10)

While the newest version of RealPlayer should be able to play any RealAudio file, other programs may not support all codecs. IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS). ... VSELP stands for Vector Sum Excited Linear Prediction and is a speech coding method used in the IS-54 standard. ... G.728 is a ITU-T standard for speech coding operating at 16 kbit/s. ... G.728 is a ITU-T standard for speech coding operating at 16 kbit/s. ... Dolby Laboratories, Inc. ... Description Dolby Digital is the trademark for Dolby Laboratories AC-3 audio coding system. ... Algebraic Code Excited Linear Prediction or ACELP is a speech encoding algorithm where a limited set of pulses is distributed as excitation to linear prediction filter. ... The cook codec is a lossy audio compression codec developed by RealNetworks. ... Sony Corporation (Japanese katakana: ソニー) (TYO: 6758), (NYSE: SNE) is a global consumer electronics corporation based in Tokyo, Japan. ... ATRAC (Adaptive TRansform Acoustic Coding) is a family of proprietary audio compression algorithms used to store information on MiniDiscs and other Sony-branded audio players. ... MPEG-4 is a standard used primarily to compress audio and visual (AV) digital data. ... Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. ... MPEG-4 is a standard used primarily to compress audio and visual (AV) digital data. ... High Efficiency AAC (HE-AAC) is a lossy data compression scheme for digital audio. ...


See also

Icecast is a free streaming media project maintained by the Xiph. ... Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. ... MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding format. ... Ogg is an open standard for a free container format for digital multimedia, unrestricted by software patents and designed for efficient streaming and manipulation. ... Vorbis is an open source, lossy audio codec project headed by the Xiph. ... Theora is a video codec being developed by the Xiph. ... SHOUTcast TV streaming in Winamp 5. ... SHOUTcast is a multiplatform freeware audio streaming technology, developed by Nullsoft. ... Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. ... MPEG-1 Audio Layer 3, more commonly referred to as MP3, is a popular digital audio encoding format. ... SHOUTcast TV streaming in Winamp 5. ... Windows Media Audio (WMA) is a proprietary compressed audio file format developed by Microsoft. ... Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... The following tables compare general and technical information for a variety of audio codecs. ...

External links


  Results from FactBites:
 
MediaCoder Audio Video Glossary (810 words)
When RealAudio was introduced, RealNetworks disclosed no technical details about the audio format or how it was encoded, but it was soon noticed that some of the audio codecs used in RealAudio were identical to those used in cellular telephones and digital television.
RealAudio was developed as a streaming media format, meaning that it can be played while it is downloaded.
In this case, the RealAudio file is retrieved similarly to a normal web page, but playback begins as soon as the first part is received and continues while the rest of the file is downloaded.
Codecs > RealAudio 10 (663 words)
RealAudio is 10 a complete audio solution that can satisfy the demands of the most discriminating audiophile to the most "bandwidth challenged".
RealAudio 10 accomplishes this by dividing original data from the audio spectrum into distinct frequency bands, some of which are perceptible by the human ear, many of which are not.
RealAudio 10 is backwards compatible with all RealAudio 8 decoders, enabling the widest possible reach across to millions of users and the last three generations of the RealPlayer.
  More results at FactBites »

 
 

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