According to reports from developers of Internet audio applications and
operators of Internet audio services, there are no standardized,
high-quality audio codecs that meet all of the following three
1. Are optimized for use in interactive Internet applications.
2. Are published by a recognized standards development organization
(SDO) and therefore subject to clear change control.
3. Can be widely implemented and easily distributed among application
developers, service operators, and end users.
There exist codecs that provide high quality encoding of audio
information, but that are not optimized for the actual conditions of the
Internet; according to reports, this mismatch between design and
deployment has hindered adoption of such codecs in interactive Internet
There exist codecs that can be widely implemented and easily
distributed, but that are not standardized through any SDO; according to
reports, this lack of standardization and clear change control has
hindered adoption of such codecs in interactive Internet applications.
There exist codecs that are standardized, but that cannot be widely
implemented and easily distributed; according to reports, the presence
of various usage restrictions (e.g., in the form of requirements to pay
royalty fees, obtain a license, enter into a business agreement, or meet
other special conditions imposed by a patent holder) has hindered
adoptions of such codecs in interactive Internet applications.
According to application developers and service operators, an audio
codec that meets all three of these would: (1) enable protocol
designers to more easily specify a mandatory-to-implement codec in
their protocols and thus improve interoperability; (2) enable
developers to more easily easily build innovative, interactive
applications for the Internet; (3) enable service operators to more
easily deploy affordable, high-quality audio services on the Internet;
and (4) enable end users of Internet applications and services to enjoy
an improved user experience.
The goal of this working group is to ensure the existence of a single
high-quality audio codec that is optimized for use over the Internet and
that can be widely implemented and easily distributed among application
developers, service operators, and end users. At present it appears
that ensuring the existence of such a codec will require a development
effort within the working group, however if a candidate codec is
presented that achieves the goal then the working group should seriously
consider stopping its development work.
The core technical considerations for such a codec include, but
are not necessarily limited to, the following:
1. Designing for use in interactive applications (examples include, but
are not limited to, point-to-point voice calls, multi-party voice
conferencing, telepresence, teleoperation, in-game voice chat, and live
2. Addressing the real transport conditions of the Internet as
identified and prioritized by the working group
3. Ensuring interoperability and clean integration with the Real-time
Transport Protocol (RTP), including secure transport via SRTP
4. Ensuring interoperability with Internet signaling technologies such
as Session Initiation Protocol (SIP), Session Description Protocol
(SDP), and Extensible Messaging and Presence Protocol (XMPP); however,
the result should not depend on the details of any particular signaling
Optimizing for very low bit rates (typically below 2.4 kbps) and for
non-interactive audio is out of scope because such work might
necessitate specialized optimizations.
Although a codec produced by this working group or another standards
organization might be used as a mandatory-to-implement technology by
designers of particular Internet protocols, it is explicitly not a goal
of the working group to produce or select a codec that will be mandated
for use across the entire IETF or Internet community nor would their be
any expectation that this would be the only mandatory-to-implement
Based on the working group's analysis of the design space, the working
group might determine that it needs to produce more than one codec, or a
codec with multiple modes; however, it is not the goal of working group
to produce more than one codec, and to reduce confusion in the
marketplace the working group shall endeavor to produce as few codecs as
In completing its work, the working group should collaborate with other
IETF working groups to complete particular tasks. These might include,
but would not be limited to, the following:
- Within the AVT WG, define the codec's payload format for use with the
Real-time Transport Protocol (RTP).
- Collaborate with working groups in the Transport Area to identify
important aspects of packet transmission over the Internet.
- Collaborate with working groups in the Transport Area to understand
the degree of rate adaptation desirable, and to reflect that
understanding in the design of a codec that can adjust its
transmission in a way that minimizes disruption to the audio.
- Collaborate with working groups in the RAI Area to ensure that
information about and negotiation of the codec can be easily
represented at the signaling layer.
In accordance with the liaison agreement in place, the working group
will continue to coordinate with the ITU-T (Study group 16), with the
intent of submitting the completed codec RFC for co-publication by the
ITU-T if the ITU-T finds that appropriate. The working group will
communicate a detailed description of the requirements and goals to
other SDOs including the ITU-T, 3GPP, and MPEG to help determine if
existing codecs meet the requirements and goals. Information about
codecs being standardized will be available to other SDOs in the form of
internet drafts and the working group welcomes technical feedback from
other SDOs and experts from other organizations.
Suggested Codec Standardization Guidelines and Requirements for
achieving the foregoing objectives are provisionally outlined in
draft-valin-codec-guidelines and draft-valin-codec-requirements
respectively; these documents will form the starting point for working
toward consensus and, if accepted as work items of the working group,
will be refined by the working group in accordance with the usual IETF
A codec that can be widely implemented and easily distributed among
application developers, service operators, and end users is preferred.
Many existing codecs that might fulfill some or most of the technical
attributes listed above are encumbered in various ways. For example,
patent holders might require that those wishing to implement the codec
in software, deploy the codec in a service, or distribute the codec in
software or hardware need to request a license, enter into a business
agreement, pay licensing fees or royalties, or attempt to adhere to
other special conditions or restrictions.
Because such encumbrances have made it difficult to widely implement and
easily distribute high-quality audio codecs across the entire Internet
community, the working group prefers unencumbered technologies in a way
that is consistent with BCP 78 and BCP 79. In particular, the working
group shall heed the preference stated in BCP 79: "In general, IETF
working groups prefer technologies with no known IPR claims or, for
technologies with claims against them, an offer of royalty-free
licensing." Although this preference cannot guarantee that the working
group will produce an unencumbered codec, the working group shall follow
BCP 79, and adhere to the spirit of BCP 79. The working group cannot
explicitly rule out the possibility of adopting encumbered technologies;
however, the working group will try to avoid encumbered technologies
that require royalties or other encumbrances that would prevent such
technologies from being easy to redistribute and use.
1. A set of Codec Standardization Guidelines that define the work
processes of the working group. This document shall be Informational.
2. A set of technical Requirements. This document shall be
3. Specification of a codec that meets the agreed-upon requirements, in
the form of an Internet-Draft that defines the codec algorithm along
with source code for a reference implementation. The text description
of the codec shall indicate which components of the encoder and decoder
are mandatory, recommended, and optional. It is envisioned that this
document shall be a Proposed Standard document.