%% You should probably cite rfc7587 instead of this I-D.
@techreport{ietf-payload-rtp-opus-11,
    number =    {draft-ietf-payload-rtp-opus-11},
    type =      {Internet-Draft},
    institution =   {Internet Engineering Task Force},
    publisher = {Internet Engineering Task Force},
    note =      {Work in Progress},
    url =       {https://datatracker.ietf.org/doc/draft-ietf-payload-rtp-opus/11/},
    author =    {Julian Spittka and Koen Vos and Jean-Marc Valin},
    title =     {{RTP Payload Format for the Opus Speech and Audio Codec}},
    pagetotal = 18,
    year =      2015,
    month =     apr,
    day =       14,
    abstract =  {This document defines the Real-time Transport Protocol (RTP) payload format for packetization of Opus-encoded speech and audio data necessary to integrate the codec in the most compatible way. It also provides an applicability statement for the use of Opus over RTP. Further, it describes media type registrations for the RTP payload format.},
}