RealAudio

Last updated
RealAudio
Filename extension
.ra, .ram
Internet media type
audio/vnd.rn-realaudio, audio/x-pn-realaudio [1]
Initial releaseApril 1995;28 years ago (1995-04)

RealAudio, or also spelled as 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.

Contents

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' 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? ] 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.

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 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 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. [3]

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. [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

Related Research Articles

The Real-Time Streaming Protocol (RTSP) is an application-level network protocol designed for multiplexing and packetizing multimedia transport streams over a suitable transport protocol. RTSP is used in entertainment and communications systems to control streaming media servers. The protocol is used for establishing and controlling media sessions between endpoints. Clients of media servers issue commands such as play, record and pause, to facilitate real-time control of the media streaming from the server to a client or from a client to the server.

Windows Media Audio (WMA) is a series of audio codecs and their corresponding audio coding formats developed by Microsoft. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. The original WMA codec, known simply as WMA, was conceived as a competitor to the popular MP3 and RealAudio codecs. WMA Pro, a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, WMA Lossless, compresses audio data without loss of audio fidelity. WMA Voice, targeted at voice content, applies compression using a range of low bit rates. Microsoft has also developed a digital container format called Advanced Systems Format to store audio encoded by WMA.

RealMedia is a proprietary multimedia container format created by RealNetworks with the filename extension .rm. RealMedia is generally used in conjunction with RealVideo and RealAudio, while also being used for streaming content over the Internet. Typically these streams are in CBR, but a container for VBR streams named RMVB has been developed.

Helix DNA was a project to produce computer software that can play audio and video media in various formats and aid in creating such media. It is intended as a largely free and open-source digital media framework that runs on numerous operating systems and processors and it was started by RealNetworks, which contributed much of the code. The Helix Community was an open collaborative effort to develop and extend the Helix DNA platform. The Helix Project has been discontinued.

<span class="mw-page-title-main">MPlayer</span> Free and open source media player

MPlayer is a free and open-source media player software application. It is available for Linux, OS X and Microsoft Windows. Versions for OS/2, Syllable, AmigaOS, MorphOS and AROS Research Operating System are also available. A port for DOS using DJGPP is also available. Versions for the Wii Homebrew Channel and Amazon Kindle have also been developed.

<span class="mw-page-title-main">FFmpeg</span> Multimedia framework

FFmpeg is a free and open-source software project consisting of a suite of libraries and programs for handling video, audio, and other multimedia files and streams. At its core is the command-line ffmpeg tool itself, designed for processing of video and audio files. It is widely used for format transcoding, basic editing, video scaling, video post-production effects and standards compliance.

xine Multimedia playback software for Unix-like systems

xine is a multimedia playback engine for Unix-like operating systems released under the GNU General Public License. xine is built around a shared library (xine-lib) that supports different frontend player applications. xine uses libraries from other projects such as liba52, libmpeg2, FFmpeg, libmad, FAAD2, and Ogle. xine can also use binary Windows codecs through a wrapper, bundled as the w32codecs, for playback of some media formats that are not handled natively.

RealVideo, or also spelled as Real Video, is a suite of proprietary video compression formats developed by RealNetworks — the specific format changes with the version. It was first released in 1997 and as of 2008 was at version 10. RealVideo is supported on many platforms, including Windows, Mac, Linux, Solaris, and several mobile phones.

<span class="mw-page-title-main">RealPlayer</span> Media player app

RealPlayer, formerly RealAudio Player, RealOne Player and RealPlayer G2, is a cross-platform media player app, developed by RealNetworks. The media player is compatible with numerous container file formats of the multimedia realm, including MP3, MP4, QuickTime File Format, Windows Media format, and the proprietary RealAudio and RealVideo formats. RealPlayer is also available for other operating systems; Linux, Unix, Palm OS, Windows Mobile, and Symbian versions have been released.

<span class="mw-page-title-main">RMVB</span>

RealMedia Variable Bitrate (RMVB) is a variable bitrate extension of the RealMedia multimedia digital container format developed by RealNetworks. As opposed to the more common RealMedia container, which holds streaming media encoded at a constant bitrate (CBR), RMVB is typically used for multimedia content stored locally. Files using this format have the file extension ".rmvb".

The following comparison of video players compares general and technical information for notable software media player programs.

3GP is a multimedia container format defined by the Third Generation Partnership Project (3GPP) for 3G UMTS multimedia services. It is used on 3G mobile phones but can also be played on some 2G and 4G phones.

ffdshow Open-source unmaintained codec library

ffdshow is an open-source unmaintained codec library that is mainly used for decoding of video in the MPEG-4 ASP and H.264/MPEG-4 AVC video formats, but it supports numerous other video and audio formats as well. It is free software released under GNU General Public License 2.0, runs on Windows, and is implemented as a Video for Windows (VFW) codec and a DirectShow filter.

FAAC or Freeware Advanced Audio Coder is a software project which includes the AAC encoder FAAC and decoder FAAD2. It supports MPEG-2 AAC as well as MPEG-4 AAC. It supports several MPEG-4 Audio object types, file formats, multichannel and gapless encoding/decoding and MP4 metadata tags. The encoder and decoder is compatible with standard-compliant audio applications using one or more of these object types and facilities. It also supports Digital Radio Mondiale.

Real Data Transport (RDT) is a proprietary transport protocol for the actual audio-video data, developed by RealNetworks in the 1990s. It is commonly used in companion with a control protocol for streaming media like the IETF's Real Time Streaming Protocol (RTSP).

Flash Video is a container file format used to deliver digital video content over the Internet using Adobe Flash Player version 6 and newer. Flash Video content may also be embedded within SWF files. There are two different Flash Video file formats: FLV and F4V. The audio and video data within FLV files are encoded in the same way as SWF files. The F4V file format is based on the ISO base media file format, starting with Flash Player 9 update 3. Both formats are supported in Adobe Flash Player and developed by Adobe Systems. FLV was originally developed by Macromedia. In the early 2000s, Flash Video was the de facto standard for web-based streaming video. Users include Hulu, VEVO, Yahoo! Video, metacafe, Reuters.com, and many other news providers.

The following comparison of audio players compares general and technical information for a number of software media player programs. For the purpose of this comparison, "audio players" are defined as any media player explicitly designed to play audio files, with limited or no support for video playback. Multi-media players designed for video playback, which can also play music, are included under comparison of video player software.

The Helix Universal Media Server was a product developed by RealNetworks and originates from the first streaming media server originally developed by Progressive Networks in 1994. It supported a variety of streaming media delivery transports including MPEG-DASH RTMP (flash), RTSP (standard), HTTP Live Streaming (HLS), Microsoft Silverlight and HTTP Progressive Download enabling mobile phone OS and PC OS media client delivery.

<span class="mw-page-title-main">Libav</span> Multimedia framework

Libav is an abandoned free software project, forked from FFmpeg in 2011, that contains libraries and programs for handling multimedia data.

References

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