A typical audio streaming system over the Internet consists of three basic elements:
- A station, a device that generates an audio stream (according to a list of audio files or by directly digitizing an analog stream from an audio card or microphone) and forwards it to a server;
- server (repeater) – a device that receives the audio stream from the station and redirects its copies to all Internet users connected to it;
- client – a device that receives the audio stream from the server and converts it to an audio signal available to the listener of the Internet radio station.
Internet radio server and client functioning is provided by standard hardware and software, so below we consider only the issues of Internet radio station operation as the most complex and responsible component. Besides audio data stream, the station transmits text metadata – for example, information about itself and about the current song, which is offered to the client for listening. The station can be a computer with installed audio player and plug-in codec (or a specialized program) or a professional hardware device that converts an analog audio stream into a digital signal.
Taking into account the requirements for station reliability, the technical solution described below implies the use of specialized professional equipment, the cost of which is quite comparable with the cost of a modern computer system. At the same time, the computer can be used as part of the station as a means of forming materials intended for broadcasting, as well as interactive interaction with the listeners. This solution provides high quality broadcasting over relatively unreliable communication channels and is designed for professional studios used by broadcasting radio stations, although it can also be used by individual users.
The professional equipment used is designed to organize the exchange of audio information over data networks using the IP protocol. Transformation of audio signal for its transfer to the server address via IP-channel is made with the help of Instreamer audio codec which can be connected to various signal sources, including microphone and audio player. The audio data coming from the server are converted by means of the Exstreamer audio codec and output to headphones or a loudspeaker. In parallel, they can be recorded in digital or analog form to the appropriate device.
In the configuration under consideration, the Internet radio station allows you to implement the following basic functions:
- preparation of audio materials on the computer;
- their registration and storage in the non-volatile memory of the transmitting device;
- broadcasting with high quality of audio materials prepared in advance in the set sequence with observance of broadcasting time schedule;
- exchange of audio messages, including messages from the microphone, using the IP protocol in real time;
- registration and storage of digital messages received from the server.
Statistical analysis of Internet radio performance is performed using appropriate programs on the included computer, and the standard capabilities of the devices used can be extended with a high-level Audio Barix Control Language, which allows writing applications for various audio codecs.
The Instreamer audio codec is a multiprotocol converter of high-quality stereo audio signals into a digital data stream transmitted over IP networks. It supports MP3, PCM, G.711 and G.722 audio data formats broadcast in TCP, UDP, Shoutcast/Icecast and Multicast RTP digital formats; provides transmission of streaming audio signals with minimum delay, guaranteeing high sound quality; has music streaming in the background and time-stop music streaming function for IP telephony applications.
Exstreamer audio codec is a multiprotocol converter of IP audio data stream in TCP, UDP and Multicast RTP formats into audio signal for its output to headphones, loudspeakers or amplifier in AACplus, MP3, Ogg Vorbis, G.711, PCM (line decoding) formats. The converters produced are adapted to work with various external devices in specified configurations. They can be used as a receiver and Internet radio player, have a slot for a MicroSD card or a USB interface to connect external flash memory.
Thus, specialized hardware and software tools, presented on the market, allow to create and successfully operate professional internet-radio stations. Such stations make it possible to broadcast high-quality audio signals to any part of the globe where the Internet is available and provide reliable and live feedback to the listeners. Internet radio is an effective means of rapid dissemination of information in a broadcast format with the possibility of statistical analysis of the number of connections and audience interest.