View source for RealAudio

{{Short description|Audio format}}{{distinguish|RealSound}}
{{Infobox file format
| name          = RealAudio
| icon          = 
| logo          = 
| screenshot    = RealAudio.webp
| caption       = 
| extension     = {{mono|.ra}}, {{mono|.ram}}
| mime          = audio/vnd.rn-realaudio, audio/x-pn-realaudio<ref>[http://service.real.com/help/faq/rp8/configrp8win.html RealPlayer 8 FAQ]</ref>
| type code     = 
| uniform type  = 
| magic         = 
| owner         = 
| genre         = 
| container for = 
| contained by  = 
| extended from = 
| extended to   = 
| standard      = 
| released      = {{start date and age|1995|4}}
| website       = {{web archive|url=https://web.archive.org/web/20040404115218/http://www.realnetworks.com/products/codecs/realaudio.html|title=realnetworks.com}}
}}
'''RealAudio''', also spelled '''Real Audio''', is a proprietary [[audio file format|audio format]] developed by [[RealNetworks]] and first released in April 1995. It uses a variety of [[audio codec]]s, 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.<ref>{{Cite web |last=Kortekaas |first=Mark |date=2009-10-07 |title=Radio Labs: RealMedia - an update |url=https://www.bbc.co.uk/blogs/radiolabs/2009/10/realmedia_an_update.shtml |access-date=2024-02-03 |website=bbc.co.uk |language=en}}</ref> [[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' [[RealPlayer SP]], currently at version 16, and is available for various platforms in binary form. Several features of this program have proven controversial (most recently, RP11's ability to record unprotected streaming media from web sites), 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,{{when?|date=November 2022}} RealNetworks has made efforts to be somewhat more open, and has founded the [[Helix Community]], a collaborative [[Open-source model|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 [[MPlayer]], and [[Real Alternative]]. However, Real Alternative does not decode the audio data by itself, but relies on the [[Dynamic Link Library|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.

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 [[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 stream transport|RDT]] protocol, which they initially kept secret. Recently, some specifications for the RDT protocol have been made public through the [[Helix Community]] project. By around 2004 the open-source MPlayer project developed a means of playing the RDT streams.<ref>[[MPlayer]] {{better citation|date=November 2011}}</ref>

In many cases, web pages do not [[hyperlink|link]] directly to a RealAudio file. Instead, they link to a .ram (Real Audio Metadata) or [[Synchronized Multimedia Integration Language|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 [[Uniform Resource Locator|URL]] from the file and then plays the stream.<ref>{{cite web|author=David Fiedler|title=RealAudio|url=http://homerecording.com/realaudio.html|work=HomeRecording.com|access-date=August 20, 2011|year=2008}}</ref>

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.

==RealAudio: Pioneering real-time music streaming in 1998==
{{Disputed section|date=May 2025}}

This section details the launch of Internet Music Net, a website credited by DJ Vinatea as one of the first, if not the very first, to offer real-time music streaming in 1998.<ref>{{cite web|author=Kuriousgeorge|title=Internet Music Net|url=http://internetmusic.net|work=InternetMusic.net|year=2024|archive-url=https://web.archive.org/web/19980710103358/http://internetmusic.net |archive-date=10 July 1998 }}</ref> The website utilized the then-pioneering RealAudio (.RA) technology, paving the way for a new era of online music consumption. 

The emergence of real-time music streaming in the late 1990s revolutionized online music access. In 1998, Internet Music Net  became a pioneer in this domain, offering users the ability to listen to music directly through their web browsers using RealAudio technology.

The development of RealAudio by Progressive Networks in the mid-1990s enabled efficient streaming of audio content over the internet. Internet Music Net capitalized on this innovation, launching in 1998 (archived on Wayback Machine) as one of the first websites to offer real-time music streaming. While details about the specific features are limited due to the archived nature of the website, it likely offered functionalities such as artist selection and genre browsing.

Internet Music Net pioneering approach paved the way for the widespread adoption of real-time music streaming services.  The concept of on-demand music access, popularized by this website, laid the groundwork for the development of future industry giants like Spotify and Pandora.

Although the ultimate fate of Internet Music Net remains unclear (e.g., did it cease operation or get acquired?), its contribution to the evolution of online music consumption remains undeniable. The website stands as a testament to the early efforts that shaped the way we experience music today.

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

* {{mono|lpcJ}}, {{mono|14_4}}: [[IS-54]] [[VSELP]] (RealAudio 1)
* {{mono|28_8}}: [[G.728]] [[LD-CELP]] (RealAudio 2)
* {{mono|dnet}}: [[Dolby Laboratories|Dolby]] [[Dolby AC-3|AC3]] (RealAudio 3)
* {{mono|sipr}}: Sipro Lab Telecom [[ACELP|ACELP-NET]] (RealAudio 4/5)
* {{mono|cook}}: G2/[[Cook Codec]] (RealAudio 6)
* {{mono|atrc}}: [[Sony Corporation|Sony]] [[ATRAC|ATRAC3]] (RealAudio 8)
* {{mono|raac}}: [[MPEG-4]] [[Advanced Audio Coding|LC-AAC]] (RealAudio 9)
* {{mono|racp}}: [[MPEG-4]] [[HE-AAC]] (RealAudio 10)
* {{mono|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.

==See also==
* [[Comparison of audio coding formats]]
* [[Icecast]] – a free and open source streaming server for internet radio stations, supports formats [[Advanced Audio Coding|AAC]], [[MP3]], [[Ogg]] [[Vorbis]], [[Theora]], and [[Nullsoft Streaming Video|NSV]]
* [[SHOUTcast]] – a freeware server for internet radio stations, supports [[Advanced Audio Coding|AAC]], [[MP3]], and [[Nullsoft Streaming Video|NSV]]
* [[Windows Media Audio]] – [[Microsoft|Microsoft's]] media formats

==References==
{{reflist}}

== External links ==
* {{web archive|url=https://web.archive.org/web/20040404115218/http://www.realnetworks.com/products/codecs/realaudio.html|title=Official website}}

{{Compression formats}}
{{Authority control}}

{{DEFAULTSORT:Realaudio}}
[[Category:Audio codecs]]
[[Category:RealNetworks|Audio]]