Short answers, pulled from the story.
SILK is an audio compression format and codec developed by Skype Limited, now a Microsoft subsidiary. It was created to replace the SVOPC codec inside Skype and was publicly announced at the Consumer Electronics Show in January 2009.
SILK supports sampling frequencies of 8, 12, 16, and 24 kHz and bitrates ranging from 6 to 40 kbit/s. It operates with an algorithmic delay of 25 milliseconds, made up of a 20 ms frame size and a 5 ms look-ahead.
SILK was first integrated into Skype in version 4.0 Beta 3, released on the 7th of January 2009. The final version of Skype 4.0 followed on the 3rd of February 2009.
The SILK codec is open-source and available royalty-free but with restrictions on use and distribution. The SDK was initially available only by application; later versions allowed download without application but limited use to internal evaluation and testing, excluding commercial products or software distribution.
SILK is one of the two foundations of Opus, the Internet standard codec. A hybrid codec combining SILK with CELT was submitted to the IETF in September 2010 under the working name Harmony and was published as an IETF proposed standard in September 2012.
Steam adopted SILK for its voice chat on the 22nd of March 2011. Team Fortress 2 integrated it on the 14th of April that same year, and the GoldSrc platform under SteamPipe adopted it on the 29th of January 2013. Zoom has also been found using SILK.