RealAudio

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RealAudio
Filename extension
.ra, .ram
Internet media type
audio/vnd.rn-realaudio, audio/x-pn-realaudio[1]
Initial releaseApril 1995; 29 years ago (1995-04)

RealAudio, also spelled Real Audio, is a proprietary audio format developed by RealNetworks and first released in April 1995. 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 be used as a streaming audio format, that is played at the same time as it is downloaded.

In the past, many internet radio stations used RealAudio to stream their programming over the internet in real time. In recent years, however, the format has become less common and has given way to more popular audio formats. RealAudio was heavily used by the BBC websites until 2009, though it was discontinued due to its declining use.[2] BBC World Service, the last of the BBC websites to use RealAudio, discontinued its use in March 2011.

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).

Players

The official player for RealMedia content is RealNetworks'

open source
project, to extend their media framework.

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.

A variety of unofficial players now exist, including

codecs which allow Windows Media Player
to play some versions of RealAudio.

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 so some alternative protocols have been developed which work better for live broadcasts.

The first version of RealAudio used a proprietary protocol called PNA or PNM to send streaming audio data. RealNetworks later switched to the

Helix Community project. By around 2004 the open-source MPlayer project developed a means of playing the RDT streams.[3]

In many cases, web pages do not

URL from the file and then plays the stream.[4]

With

RealPlayer SP, it is now possible to save an audio stream to a file. Other programs, including MPlayer, RM Downloader, VLC media player, StreamBox VCR, HiDownload and Real7ime Converter
can also save streams to a file.

Codecs

RealAudio files are compressed using several 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:

While the newest version of RealPlayer should be able to play any RealAudio file, other programs may not support all codecs.

See also

References

  1. ^ RealPlayer 8 FAQ
  2. ^ Kortekaas, Mark (2009-10-07). "Radio Labs: RealMedia - an update". bbc.co.uk. Retrieved 2024-02-03.
  3. better source needed
    ]
  4. ^ David Fiedler (2008). "RealAudio". HomeRecording.com. Retrieved August 20, 2011.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=RealAudio&oldid=1213656818"