ISO/IEC 14496-8:2004

INTERNATIONAL ISO/IEC
STANDARD 14496-8
First edition
2004-05-15
Information technology — Coding of
audio-visual objects —
Part 8:
Carriage of ISO/IEC 14496 contents over
IP networks
Technologies de l'information — Codage des objets audiovisuels —
Partie 8: Transport du contenu MPEG-4 sur les réseaux IP

Reference number
©
ISO/IEC 2004
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ii © ISO/IEC 2004 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC 14496-8 was prepared by Joint Technical Committee ISO/TC JTC 1, Information technology,
Subcommittee SC 29, Coding of audio, picture, multimedia and hypermedia information.
ISO/IEC 14496 consists of the following parts, under the general title Information technology — Coding of
audio-visual objects:
 Part 1: Systems
 Part 2: Visual
 Part 3: Audio
 Part 4: Conformance testing
 Part 5: Reference software
 Part 6: Delivery Multimedia Integration Framework (DMIF)
 Part 7: Optimized reference software for coding of audio-visual objects
 Part 8: Carriage of ISO/IEC 14496 contents over IP networks
 Part 9: Reference hardware description
 Part 10: Advanced Video Coding
 Part 11: Scene description and application engine
 Part 12: ISO base media file format
 Part 13: Intellectual Property Management and Protection (IPMP) extensions
 Part 14: MP4 file format
 Part 15: Advanced Video Coding (AVC) file format
 Part 16: Animation Framework eXtension (AFX)

© ISO/IEC 2004 – All rights reserved iii

Introduction
ISO/IEC 14496 is an International Standard designed for the representation and delivery of multimedia
information over a variety of transport protocols. It includes interactive scene management, visual and audio
representations as well as systems functionality like multiplexing, synchronization, and an object descriptor
framework. This document provides a framework for the carriage of ISO/IEC 14496 contents over IP networks
and guidelines for designing payload format specifications for the detailed mapping of ISO/IEC 14496 content
into several IP-based protocols
iv © ISO/IEC 2004 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 14496-8:2004(E)

Information technology — Coding of audio-visual objects —
Part 8:
Carriage of ISO/IEC 14496 contents over IP networks
1 Scope
This part of ISO/IEC 14496 specifies transport level functionalities for the communication of interactive audio-
visual scenes. More specifically:
1. Framework for the carriage of ISO/IEC 14496 contents over IP networks;
2. Guidelines to design RTP payload formats for ISO/IEC 14496 contents including fragmentation and
concatenation rules;
3. Usage rules of SDP to transport ISO/IEC 14496-1 related information;
4. MIME type definitions for ISO/IEC14496 contents; and
5. Analysis on RTP Security and Multicasting.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
IETF RFC 1889, RTP A Transport Protocol for Real-Time Applications
IETF RFC 1890, RTP Profile for Audio and Video Conference with Minimal Control
IETF RFC 2326, Real Time Streaming Protocol (RTSP)
IETF RFC 2327, SDP: Session description protocol
IETF RFC 3016, RTP payload format for MPEG-4 audio/visual streams
IETF RFC 3640, Transport of MPEG-4 elementary streams
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
MIME
Multipurpose Internet Mail Extensions, referring to an official Internet standard that identifies the format of the
contents exchanged over different systems connected to the network
© ISO/IEC 2004 – All rights reserved 1

3.2
RTP
Real Time Transport Protocol, an Internet protocol used for transport of multimedia data
3.3
RTSP
Real Time Streaming Protocol, an application-level Internet protocol for control over the delivery of data with
real-time properties
3.4
RTCP
Real Time Transport Control Protocol, an Internet protocol used to configure RTP packets and to control the
transport of RTP packets
3.5
SDP
an Internet protocol used for describing multimedia sessions for the purposes of session announcement,
session invitation, and other forms of multimedia session initiation
4 Symbols and abbreviated terms
AAC Advanced Audio Coding
AU Access Unit
BIFS Binary Format for Scene
CELP Code Excited Linear Prediction
CTS Composition Time Stamp
ES Elementary Stream
ESI Elementary Stream Interface
ESID Elementary Stream Identifier
FCR FlexMux Clock Reference
IETF Internet Engineering Task Force
MIME Multipurpose Internet Mail Extensions
OCR Object Clock Reference
OD Object Descriptor
ODID Object Descriptor Identifier
QoS Quality of Service
RFC Request For Comments
SL Synchronization Layer
SL-Packet Synchronization Layer Packet
URL Universal Resource Locator
2 © ISO/IEC 2004 – All rights reserved

5 Use of RTP
5.1 Introduction
There are a number of RTP packetization schemes for ISO/IEC 14496 data. Media-aware packetization (e.g.
video frames split at recoverable sub-frame boundaries) is a principle in RTP, and thus it is likely that several
RTP schemes will be needed, to suit both the different kinds of media — audio, video, etc. — and different
encodings (e.g. AAC and CELP audio codecs).This specification does not specify any payload format but do
specify a general framework to design and utilize the payload formats in appropriate way.
This specification requires that, no matter what packetization scheme is used, there are a number of common
characteristics that all shall have: however, such characteristics depend on the fact that the RTP Session
contains a single elementary stream or a flexmux stream.
5.2 Carrying a single elementary stream
In case an RTP Session contains a single elementary stream the following characteristics apply:
• The RTP timestamp corresponds to the presentation time (e.g. CTS) of the earliest AU within the packet.
• RTP packets have sequence numbers in transmission order. The payloads logically or physically have SL
Sequence numbers, which are in decoding order, for each elementary stream.
• The ISO/IEC 14496 timescale (clock ticks per second), which is timeStampResolution in the case of
ISO/IEC 14496 Systems, shall be used as the RTP timescale, e.g. as declared in SDP for an RTP stream.
• To achieve a base level of interoperability, and to ensure that any ISO/IEC 14496 stream may be carried,
all receivers should implement a generic payload format defined in “draft-ietf-avt-mpeg4-multisl-04.txt” as
default RTP payload mapping scheme. Any new payload format should be a configurable subset of the
generic payload format.
• Streams should be synchronized using RTP techniques (notable RTCP sender reports). When the
ISO/IEC 14496 OCR is used, it is logically mapped to the NTP time axis used in RTCP.
• The RTP packetization schemes may be used for ISO/IEC 14496 elementary streams 'standing alone'
(e.g. without ISO/IEC 14496 systems, including BIFS); or they may be used within an overall presentation
using the object descriptor framework. In the latter case, a SLConfigDescriptor is sent describing the
stream. Logically, each RTP stream is passed through a mapping function which is specific to the payload
format used; this mapping function yields a SL packetized stream. The SLConfigDescriptor describes this
logical stream, not the actual bits in the RTP payload. For example, the RTP sequence number may be
used to make the SLPacketHeader sequence number; other SL fields may be set in this way, dynamically,
or from static values in the payload specification. For example, as all RTP packets carry a composition
time-stamp, the flag in the SL header indicating its presence can normally be statically defined as 'true'.
Each payload format for ISO/IEC 14496 content shall specify the mapping function for the formation of
the SLConfigDescriptor and the SLPacketHeader. In the case of the RFC 3016, the mapping shall be
defined in a seperate document.
© ISO/IEC 2004 – All rights reserved 3

Figure 1 — RTP packet to SL packet mapping
5.3 Payload format selection
Other payload formats may be used. They are signalled as dynamic payload IDs, defined by a suitable name
(e.g. a payload name in an SDP RTPMAP attribute). In particular, the development of specialized RTP
payloads for video (e.g. respecting video packets) and audio (e.g. providing interleave) is expected. It is
possible that these schemes can be compatible with the default scheme required here.
There may be a choice of RTP payload formats for a given stream (e.g. as an elementary stream, an SL-
packetized stream, using FlexMux, and so on). It is recommended that
• terminals implementing a given subsystem (e.g. video) accept at least an ES and the default SL packings
of that stream; for example, this means accepting the RFC 3016 and also the generic payload format for
MPEG-4 Visual;
• terminals implementing a given payload format accept any stream over that format for which they have a
decoder, even if that packing is not normally the 'best' packing.
5.4 ISO/IEC 14496 QoS considerations
For those streams requiring a certain Quality of Service (specifiable appropriately), the recommendation is to
further investigate possible solutions such as the leverage of existing work in the IETF in this area (including,
but not limited to FEC, re-transmission, or repetition). However, techniques in data-dependent error correction,
or combined source/channel coding solutions make other schemes attractive. Also, it is recommended that
requirement such as efficient grouping mechanisms (i.e. the ability to send in a single RTP packet multiple
consecutive AUs, each with its own SL information) and low overhead is also taken into account.
4 © ISO/IEC 2004 – All rights reserved

6 Usage of SDP attributes
This specification considers only ISO/IEC 14496 Systems related issues. Usage of SDP information for
specific payload format shall be specified in each RTP payload format RFCs. The usage of elementary
streams in other contexts is not addressed here: codepoints for this case are specified in, and in other places.
This specification currently assumes that any session described by SDP (e.g. in SAP, as a file download, as a
DESCRIBE over RTSP) has at most one ISO/IEC 14496 session. It is desirable that this restriction be lifted.
• Senders should alert receivers that an ISO/IEC 14496 session is included, by means of an SDP attribute
that is general (i.e. before any "media" lines). This takes the form of the following attribute line:
a=mpeg4-iod []
location: In an RTSP session, this is an optional attribute. If not supplied, the IOD is retrieved over the
RTSP session by using DESCRIBE with an accept of type application/mpeg4-iod or application/mpeg4-
iod-xmt. Where the SDP information is supplied by some other means (e.g. as a file, in SAP), the location
is obligatory. The location should be a URL enclosed in double-quotes, which will supply the IOD (e.g.
small ones may be encoded using "data:", otherwise "http:" or other suitable file-access URL). When
application/mpeg4-iod-xmt type is used, the IOD in XMT format shall be supplied. The
InitialObjectDescriptor is defined in subclause 8.6.3.1 of ISO/IEC 14496-1:2001 and its XMT format is
defined in subclause 15.8.3. of ISO/IEC 14496-1:2001 AMD2. Any ter
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