I have started testing the Opus 0.9.0 experimental codec in a recent build of FreeSWITCH - thanks to Anthony Minessale for writing the module, and thanks to William F. Acker for helping with the testing. For those who aren't familiar with it, Opus is a combination of CELT and SILK, which is currently under discussion within the IETF. After building and loading the module, specify Opus-0.9.0 as your codec. The versioning of the codec's name is a good idea; this should prevent mutually incompatible versions from interacting with each other as development of the codec proceeds. My initial impressions are favourable; the audio quality is comparable to CELT at 48 khz, based on my early listening experience. I did notice some occasional pops in the audio, presumably attributable to packet loss. SILK apparently has some error correction functionality built in, but I don't know what its status is in the combined Opus codec. If it's present, then it didn't smooth out the glitches, at least in my environment.