Opus

Description
Opus is a lossy audio compression format designed by the Internet Engineering Task Force (IETF) for applications requiring high-quality, low-delay audio transmission (e.g. telephony or network music performance). It incorporates technology from Skype's SILK codec and Xiph.org's CELT codec.

Information

 * RFC 6716 - Definition of the Opus Audio Codec
 * Ogg Encapsulation for the Opus Audio Codec (draft-ietf-codec-oggopus-00)
 * RTP Payload Format for Opus Speech and Audio Codec (draft-spittka-payload-rtp-opus-03)
 * Opus, the Swiss Army Knife of Audio Codecs (Presentation at linux.conf.au 2012]

Software
The Opus Codec downloads page contains opus-tools (encode / inspect / decode) .opus files and opusfile, an API for developers.

foobar2000 can play back and encode Opus files (with the Free Encoder Pack

Links

 * Bitstream conformance set
 * The .opus test set (including intentionally malformed files)