 | |
| Developer(s) | Skype Limited,Microsoft |
|---|---|
| Initial release | 2009; 16 years ago (2009) |
| Stable release | 1.0.9 / 2012; 13 years ago (2012) |
| Written in | C,C++ |
| Operating system | Microsoft Windows,macOS,Linux,Android,iOS |
| Predecessor | SVOPC |
| Successor | Satin |
| Type | Audio codec |
| License | BSD 2-Clause License[1] |
| Filename extension | .sil, .SIL |
|---|---|
| Internet media type | audio/SILK |
| Magic number | #!SILK\n |
| Initial release | March 2009; 16 years ago (2009-03) |
| Latest release | SDK 1.0.9 2012; 13 years ago (2012) |
| Type of format | Audio |
| Extended to | Opus |
| Standard | Internet Draft |
SILK is anaudio compression format andaudio codec developed bySkype Limited, now aMicrosoft subsidiary. It was developed for use inSkype, as a replacement for theSVOPC codec. Since licensing out, it has also been used by others. It has been extended to the Internet standardOpus codec.
Skype Limited announced that SILK can use asampling frequency of 8, 12, 16 or 24 kHz and abit rate from 6 to 40 kbit/s. It can also use a low algorithmicdelay of 25 ms (20 ms frame size + 5 ms look-ahead).[2] The reference implementation is written in the C programming language. The codec technology is based onlinear predictive coding (LPC).[3] The SILKbinarySDK is available.[4]
The SILK codec is patented and licensed separately from the SILK SDK.[5] The codec isopen-source,freeware, availableroyalty free with restrictions on use and distribution.[4][6][7] The SDK was initially available only by application by giving details of name, address, phone, and description of how SILK will be used.[4] As of 2012[update] (version 1.0.9) the SDK can by downloaded without application, but the licence restricts the use to internal evaluation and testing purposes only, excluding software distribution or use in any commercial product or service.[4][8]
SILK replaces the previously usedSVOPC in Skype, which was a in-house solution to replace theiSAC andiLBC, which again were licensed fromGlobal IP Solutions. The SILK codec was a separate development branch from SVOPC and it has been under development for over 3 years.[9] It was announced in January 2009 on theConsumer Electronics Show[9] and was integrated in Skype for the first time in version 4.0 beta 3 from January 7, 2009,[10] with the final version being released on February 3.[11]On March 3, 2009 Skype Limited announced that the SILK codec will be available soon under aroyalty free license to third-party software and hardware developers.[6]The first draft of theSILK Speech Codec description was submitted to theInternet Engineering Task Force (IETF) as a candidate for the standardisation of a new Internet wideband audio codec on July 6, 2009, thereby openly publishing the format along with the source code of the reference implementation.[12] There is also a first draft of theRTP Payload Format and File Storage Format for SILK Speech and Audio Codec.[13]
SILK is a foundation (withCELT) of the hybrid codecOpus (at the time called "Harmony") that was submitted to the IETF in September 2010,[14] and was chosen as the final candidate for the new standard. Opus was published as an IETF proposed standard in September 2012[15] and Skype announced that they would be using Opus going forward.[16]
