A software platform for multiway audio distribution over the Internet

The Robust Audio Tool (RAT) allows users to achieve real-time multiway communication over the Internet. It was initially intended for use in multiway conferences, but is being used as an Internet audio broadcast application, by radio stations in the US and elsewhere. RAT can also be used in a point-to-point manner, and as a transcoder between networks of differing capabilities, e.g. for mobile access to the Internet. The emphasis of work in RAT has been on maximising the audio quality despite inherent problems of packet transport, processor scheduling and audio capabilities of the end system. The important features of RAT, in comparison to other Internet audio tools, is that it is able to support multirate processing, has no restrictions on audio frame duration, and supports multi-channel audio, and both fixed and variable size audio frames. We discuss methods of real-time multimedia delivery, and identify issues of particular importance for music transmission over the Internet. For music coding researchers interested in using RAT to exploit their research, we present an overview of the architecture of the RAT and specifically focus on codec integration. Finally, we present some off-line performance measurements of a public domain MPEG1 music codec that has been integrated into the RAT, and illustrate the Internet performance in terms of packet loss, and variable transit delays.