Silk (codec)
Encyclopedia
SILK is an audio compression
format and audio codec
used by Skype
. It is developed by Skype Limited. SILK is a replacement for the SVOPC
codec.
The SILK codec was a separate development branch from SVOPC and it has been under development for over 3 years.
The stable version of SILK was first introduced in Skype 4.0 Beta 3 for Windows, released on January 7, 2009. The final version of Skype 4.0 was released on February 3, 2009. On March 3, 2009 Skype Limited announced that the SILK codec will be available soon under a royalty free
license to third-party software and hardware developers. To request the SILK binary
SDK
, one must send an email with some mandatory information, e.g. name, address, phone, description of how SILK will be used, etc.
Skype Limited announced that SILK can use a sampling frequency of 8, 12, 16 or 24 kHz and a bit rate
from 6 to 40 kbit/s. It can also use a low algorithmic delay
of 25 ms (20 ms frame size + 5 ms look-ahead).
The first draft of the SILK Speech Codec description was submitted to the IETF on July 6, 2009. There is also a first draft of the RTP
Payload Format and File Storage Format for SILK Speech and Audio Codec. In September 2010 a draft of the Harmony codec which uses SILK and CELT
was submitted to the IETF. In October 2010, the Harmony codec was renamed to Opus
.
On March 22, 2011 the Steam game platform started using the SILK codec for its integrated in-game and community voice chat. Later in 14 April, in Team Fortress 2
, the codec was implemented into the in-game voice chat.
Audio compression
Audio compression may refer to:*Audio compression , a type of lossy compression in which the amount of data in a recorded waveform is reduced for transmission with some loss of quality, used in CD and MP3 encoding, Internet radio, and the like...
format and audio codec
Audio codec
All codecs are devices or computer programs capable of coding or decoding a digital data stream or signal.The term audio codec has two meanings depending on the context:...
used by Skype
Skype
Skype is a software application that allows users to make voice and video calls and chat over the Internet. Calls to other users within the Skype service are free, while calls to both traditional landline telephones and mobile phones can be made for a fee using a debit-based user account system...
. It is developed by Skype Limited. SILK is a replacement for the SVOPC
SVOPC
SVOPC is a compression method for audio which is used by applications such as Skype. It is a lossy speech compression codec designed specifically towards communication channels suffering from packet loss...
codec.
The SILK codec was a separate development branch from SVOPC and it has been under development for over 3 years.
The stable version of SILK was first introduced in Skype 4.0 Beta 3 for Windows, released on January 7, 2009. The final version of Skype 4.0 was released on February 3, 2009. On March 3, 2009 Skype Limited announced that the SILK codec will be available soon under a royalty free
Royalty free
Royalty-Free, or RF, refers to the right to use copyrighted material or intellectual property without the need to pay royalties for each use or per volume sold, or some time period of use or sales.-Computer standards:...
license to third-party software and hardware developers. To request the SILK binary
Executable
In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...
SDK
Software development kit
A software development kit is typically a set of software development tools that allows for the creation of applications for a certain software package, software framework, hardware platform, computer system, video game console, operating system, or similar platform.It may be something as simple...
, one must send an email with some mandatory information, e.g. name, address, phone, description of how SILK will be used, etc.
Skype Limited announced that SILK can use a sampling frequency of 8, 12, 16 or 24 kHz and a bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
from 6 to 40 kbit/s. It can also use a low algorithmic delay
Latency (audio)
Latency refers to a short period of delay between when an audio signal enters and when it emerges from a system...
of 25 ms (20 ms frame size + 5 ms look-ahead).
The first draft of the SILK Speech Codec description was submitted to the IETF on July 6, 2009. There is also a first draft of the RTP
Real-time Transport Protocol
The Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and...
Payload Format and File Storage Format for SILK Speech and Audio Codec. In September 2010 a draft of the Harmony codec which uses SILK and CELT
CELT
Constrained Energy Lapped Transform is an open, royalty-free audio compression format and a free software codec with especially low algorithmic delay for use in low-latency audio communication. It is a lossy codec, meaning quality is permanently degraded to reduce file size.The algorithms are...
was submitted to the IETF. In October 2010, the Harmony codec was renamed to Opus
Opus (codec)
Opus is a low-delay wideband codec intended for applications such as VoIP that will eventually be royalty-free. Opus incorporates technology from the speech-oriented SILK codec and the low-latency CELT codec...
.
On March 22, 2011 the Steam game platform started using the SILK codec for its integrated in-game and community voice chat. Later in 14 April, in Team Fortress 2
Team Fortress 2
Team Fortress 2 is a free-to-play team-based first-person shooter multiplayer video game developed by Valve Corporation. A sequel to the original mod Team Fortress based on the Quake engine, it was first released as part of the video game compilation The Orange Box on October 10, 2007 for Windows...
, the codec was implemented into the in-game voice chat.
Sources
- Stanford, M. - "Skype's new super-wideband codec"
- Skype Developer Information - "SILK – Super Wideband Audio Codec"