A Virtual Audio Driver for the Internet Speaker

We have developed the “Internet Speaker” (IS), a network-enabled single board computer embedded into a conventional audio speaker. Audio streams are transmitted in the LAN using multicast packets, and the IS can select any one of them and play it back. A key requirement for the IS is that it must be capable of playing any type of audio stream, independent of the streaming protocol, or the encoding used. We achieved this by providing a streaming audio server built as a virtual audio device (VAD) in the OpenBSD kernel. The VAD accepts input from any of the existing audio file players, or streaming audio clients. Since all audio applications have to be able to use the system audio driver, our system can accommodate any protocol or file format, provided there exists some compatible player running under OpenBSD. In this paper we discuss the design and implementation of the server as a VAD, the streaming protocol developed for this application, and the implementation of the client.