What is a RA file?

Launched in April 1995 by RealNetworks, Inc., RealAudio (RA) is a proprietary audio format that pioneered internet streaming. Identified by its .ra file extension, the format was versatile, supporting both low-bitrate codecs for dial-up connections and high-fidelity codecs for better sound quality. This technology became the backbone for countless internet radio stations and major broadcasters, most notably the BBC website, which utilized RA extensively before finally discontinuing the service in March 2011.

File Extension by RealNetworks

RealNetworks used the RA file format for audio. RealNetworks started offering video format (RealVideo) in 1997 with the .rv extension. RealMedia (RM) was used for the combination of audio and video formats. With the latest release of RealProduce (Real’s encoder), RV format is used for video files and RealMedia Variable Bitrate (RMVB) format is used for VBR (Variable bitrate) video files.

Key Characteristics of RA Files

Streaming Audio

RA was developed as a streaming media format and can be streamed using HTTP. The audio file starts playing as soon as the first part of the file is received and continues playing as the rest of the file is downloaded.

The first version of the RealAudio used the proprietary PNA or PNM protocol to stream audio. Later they switched to IETF standardized RTSP (Real Time Streaming Protocol) to manage connections. To send data, they used the RDT (Real Data Transfer) protocol. The protocol was kept secret initially but later some of it was made public through the Helix project.

To stream RealAudio files, the majority of pages link to the RAM (Real Audio Metadata) or SMIL (Synchronized Multimedia Integration Language) file. This file is used to load the user’s media player and stream the audio from the URL contained in the file.

RealAudio Audio Codecs

Here is a list of audio codecs each identified by a four character code along with the version of RealAudio that introduced it.

References

• RealAudio - Wikipedia