RealAudio

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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.

The first version of RealAudio was released in 1995. As of 2006, the current version is RealAudio 10.

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.

Codecs

RealAudio files are compressed using several different audio codecs. Each codec is identified by a four character code FourCC. Below is a list of the codecs and the version in which each was introduced:

  • 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 10)
  • racp: MPEG-4 HE-AAC (RealAudio 10)
  • ralf: RealAudio Lossless Format (RealAudio 10)

See Also


This article is licensed under the GNU Free Documentation License. It uses material from the article: RealAudio on the WIKIPEDIA

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