Internet Low Bitrate Codec (iLBC) is a

royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standard ...

narrowband Narrowband signals are signals that occupy a narrow range of frequencies or that have a small fractional bandwidth. In the audio spectrum, narrowband sounds are sounds that occupy a narrow range of frequencies. In telephony, narrowband is usua ...

speech Speech is a human vocal communication using language. Each language uses phonetic combinations of vowel and consonant sounds that form the sound of its words (that is, all English words sound different from all French words, even if they are th ...

audio coding format and an

open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use the source code, design documents, or content of the product. The open-source model is a decentralized so ...

reference implementation (

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...

), developed by Global IP Solutions (GIPS) formerly Global IP Sound (acquired by Google Inc in 2011). It was formerly

freeware Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines ''freeware'' unambiguously; every publisher defines its own rules for the ...

with limitations on commercial use, but since 2011 it is available under a

free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, n ...

/open source ( 3-clause BSD license) license as a part of the open source WebRTC project. It is suitable for

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

applications, streaming audio, archival and messaging. The algorithm is a version of block-independent

linear predictive coding Linear predictive coding (LPC) is a method used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive mod ...

, with the choice of

data frame A frame is a digital data transmission unit in computer networking and telecommunication. In packet switched systems, a frame is a simple container for a single network packet. In other telecommunications systems, a frame is a repeating structu ...

lengths of 20 and 30 milliseconds. The encoded blocks have to be encapsulated in a suitable protocol for transport, usually the

Real-time Transport Protocol The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP networks. RTP is used in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applicati ...

(RTP). iLBC handles lost frames through graceful speech quality degradation. Lost frames often occur in connection with lost or delayed IP packets. Ordinary low-bitrate codecs exploit dependencies between speech frames, which cause errors to propagate when packets are lost or delayed. In contrast, iLBC-encoded speech frames are independent and so this problem will not occur. iLBC is defined in RFC 3951. It is one of the codecs used by Gizmo5, WebRTC, Ekiga,

Google Talk Google Talk was an Instant messaging, instant messaging service that provided both text and voice communication. The instant messaging service was variously referred to colloquially as Gchat, Gtalk, or Gmessage among its users. Google Talk was ...

, Maemo Recorder (on the Nokia N800/ N810), Polycom IP Phone,

Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...

, QuteCom, Tuenti, Yahoo! Messenger,

Ooma Ooma, Inc. is an American publicly traded telecommunications company based in the Silicon Valley, California area. Ooma offers communications services including Voice over IP (VoIP) calling for business, home and mobile users. History Oo ...

and many others. iLBC was submitted to IETF in 2002 and the final specification was published in 2004.

Parameters and features

Sampling frequency In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or s ...

8 kHz/16 bit (160 samples for 20 ms frames, 240 samples for 30 ms frames) * Controlled response to

packet loss Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion.Ku ...

, delay and

jitter In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signific ...

* Fixed bitrate (15.2 kbit/s for 20 ms frames, 13.33 kbit/s for 30 ms frames) * Fixed frame size (304 bits per block for 20 ms frames, 400 bits per block for 30 ms frames) * Robustness similar to

pulse-code modulation Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the ...

(PCM) with packet loss concealment, like the

ITU The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Union ...

-T G.711 * CPU load similar to G.729A, with higher basic quality and better response to packet loss *

Royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standard ...

* Since 2011 it is available under an open source ( 3-clause BSD license) license as a part of the open source WebRTC project. (previously commercial use of the source code supplied by GIPS required a licenceformer GIPS license
) * PSQM testing under ideal conditions yields mean opinion scores of 4.14 for iLBC (15.2 kbit/s), compared to 4.3 for G.711 ( μ-law)

References

External links

Official homepage

iLBC former homepage
{{Compression Software Implementations Speech codecs Free audio codecs Open formats Software using the BSD license Formerly proprietary software

Parameters and features

See also

References

External links