Network Working GroupS. Pfeiffer
Internet-DraftC. Parker
Expires: June 30, 2004A. Pang
 December 31, 2003

The Annodex annotation format for time-continuous bitstreams, Version 2.0


Status of this Memo

This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 except that the right to produce derivative works is not granted.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

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This Internet-Draft will expire on June 30, 2004.

Copyright Notice

Copyright (C) The Internet Society (2003). All Rights Reserved.


This specification defines a file format for annotating and indexing time-continuous bitstreams for the World Wide Web. The format has been named "Annodex" for annotating and indexing. The Annodex format enables the specification of named anchor points in time-continuous bitstreams together with textual annotations and hyperlinks in URI[4] format. These anchor points are merged time-synchronously with the time-continuous bitstreams when authoring a file in Annodex format. The ultimate aim of the Annodex format is to enable an integration of time-continous bitstreams into the browsing and searching functionality of the World Wide Web.

At this point in time, the right to produce derivative works is not granted to the IETF as the authors are uncertain about the necessity to create a working group. The specification is not encumbered by patents. The Annodex format is protected by a trade mark to prevent the use of the term "Annodex" for any related but non-conformant and therefore non-interoperable technology. Conformant technology is encouraged to use the term "Annodex" when refering to the file format.

Notice the change to Annodex 2.0 from the previous version of this Internet-Draft, replacing Annodex 1.0.

Table of Contents

1.  Introduction
2.  The architecture of a Continuous Media Web
3.  Overview of the Annodex bitstream format
4.  Handling time in the Annodex format bitstream
5.  Media encapsulation format
5.1  Media mapping for Ogg encapsulation
5.2  The format of the Annodex media mapping bos
5.3  The format of the media and annotation bitstream media mapping bos
6.  The decoding of Annodex format bitstreams to CMML
7.  MIME media type registration for 'application/annodex'
7.1  URI addressing into Annodex files
7.1.1  Query parameters for use with the HTTP protocol server-side
7.1.2  Fragment identifiers for use with the HTTP protocol client-side
7.1.3  HTTP 'Accept' header field interpretation
8.  Security considerations
§  References
§  Authors' Addresses
A.  Definitions of terms and abbreviations
B.  Glossary of acronyms
C.  Acknowledgements
§  Intellectual Property and Copyright Statements


1. Introduction

When searching the World Wide Web, time-continuous data such as audio and video files are still treated as "dark matter" outside the existing infrastructure of the World Wide Web. It is not possible to look inside such files, search for their content through common text-based search engines, and directly hyperlink to points of interest inside them. The file can only be consumed in its entirety until the point of interest is reached. In addition, such files are "dead ends" in that by consuming their content the hyperlinking functionality of the Web is left behind.

This document specifies a file format that enables integrated handling of time-continuous data on the World Wide Web. By interleaving XML markup with the time-continuous data, the internal structure and content of the time-continuous data file becomes accessible, the file becomes annotated and indexed, or a "Annodex" file. The Annodex format together with the Continuous Media Markup Language (CMML)[15] and the URI standard[4], extended by temporal URI references[14] build the basis technology to enable searching and surfing of time-continuous data via existing Web infrastructure. The Annodex format enables encapsulation of any type of streamable time-continuous bitstream format thus being independent of current or future compression formats. The XML tags were chosen to be very similar to XHTML to enable a simple transfer of knowledge for HTML authors.

The file extension of Annodex files is ".anx". This document also applies for registration of the mime-type "application/annodex" for Annodex format bitstreams.

The structure of this document is as follows: this introduction is followed by a section describing the architecture of a Continuous Media Web based on Annodex format data. The next section gives an overview of the Annodex file format, including the annotation bitstream. The handling of the different time constructs in Annodex is quite complex and is explained in section 4. Section 5 then describes in detail how media encapsulation is performed and what the multiplexing format consists of. How to extract the annotation and meta data content of an Annodex stream into a CMML file is explained in section 6. The MIME type application and security considerations constitute the final sections.

Please note that this document assumes that the reader has a fluent working knowledge of XML[1], HTML[2], XHTML[3] and the World Wide Web. Deep knowledge of the Ogg encapsulation format version 0[11] is also a prerequisite to understanding this specification. It is also a sister document to the specification of the Continous Media Markup Language (CMML Version 2.0)[15] for authoring annotations for time-continuous data and for steering the encoding of Annodex format bitstreams.


2. The architecture of a Continuous Media Web

As with Webpages, Annodex format bitstreams first have to be authored and then published on a server. Authoring includes the creation of the media bitstream plus the creation of annotations (i.e. textual data descriptions), indexes (i.e. anchor points) and hyperlinks (i.e. URIs[4]) for clips of the media data. Annotations, indexes and hyperlinks are created in "head" and "clip" tags conformant to the CMML[15] specification, and interleaved into the media document to create Annodex format bitstreams in a time-synchronous fashion. This procedure can be performed both on files and live streams. The collection of Annodex format bitstreams on the Internet is called the Continuous Media Web as it builds a Web of time-continuous resources.

Distribution of Annodex format bitstreams happens via a network protocol such as HTTP[5] or RTP/RTSP[7]. The basic process is the following: The client dispatches a download or streaming request to the server with a certain URI. The server resolves the URI and starts packetising Annodex format bitstreams, taking into account URI addressed offsets or fragments. Currently the distribution with HTTP is clear and discussed in this document, while the details of a distribution via RTP/RTSP are not yet examined and thus unspecified.

The Annodex format has been designed to accommodate for reliable and unreliable transport. In case of packet loss due to an unreliable transport, media data or clip data may get lost; this may be important to the application or not. Both media and mark-up data are treated with the same importance. If a user doesn't care whether the media data is completely received, then the mark-ups will be regarded the same way. Clips are typically treated as state changes; if a clip tag is lost, the next clip tag will restore the proper state. We envisage, however, that a client may require the current state information, so there should be a protocol request for sending the current state again. This will be delivered by the server by inserting another copy of the currently active clip into the Annodex bitstream.

To access the Continuous Media Web, a client such as a conformant Web browser is required. A client can link to an Annodex bitstream via a URI. A URI can point to a temporal offset in the Annodex bitstream using URI time interval specifierss[14] or to a named offset by using the id tag of a clip element as a URI fragment identifier. In this way, direct access to points of interest in the media document is enabled. While playing back Annodex format bitstreams, a user is being offered hyperlinks (URIs) to other Web resources which are related to the currently displayed media content.

A client may be a special player or a browser plugin. This application must split an Annodex format bitstream into its constituent time-continuous data streams and the annotation bitstream consisting of "head" and "clip" tags. A decoder is required to display the encapsulated media document after decoding it with the appropriate media decoder. While playing back the media document, the application displays the hyperlinks and the annotations for the active clips.

Search engines can include published Annodex format files into their search repertoire by finding annotations in the clip tags in a standard way independent of the encoding and packetising format of the annodexed time-continuous data streams. This allows any media format to be spidered. In addition, the protocol should allow the downloading of only the CMML mark-up from a published Annodex format file in order to discourage spiders from creating extensive network loads, as they do not need to download the media bitstream to gain the necessary information. It also reduces the size of search archives, even for large amounts of published Annodex format files, because a CMML file contains all searchable annotations for the clips of its Annodex format file.


3. Overview of the Annodex bitstream format

The format of Annodex bitstreams consists of interleaved bitstreams of time-continuous data and structured XML mark-up of an annotation bitstream. It is designed to be used both as a persistent file format and as a streaming format. Any encoding format for time-continuous data can be encapsulated in the Annodex format as long as it is streamable and is based on a regular data sampling rate (called granulerate). XML mark-up is inserted between data packets at the synchronised point in time.

An Annodex bitstream is designed to allow several tracks of temporally synchronous time-continuous data. Each bitstream track represents codec data for one type of time-continuous data stream. The annotation bitstream is regarded as one of these data bitstreams representing a CMML[15] file. It annotates the Annodex bitstream by subdividing it sequentially into clips of data and providing annotations for it. Several annotation tracks may be represented in on annotation bitstream, allowing to describe the Annodex bitstream from different aspects, e.g. by giving different language tracks, or representing a shot structure and a scene structure. Thus an Annodex bitstream has the following conceptual structure:

  Annodexed media file with data bistreams D1-D3 and an annotation bitstream
  with two annotation tracks A1, A2:

D1  |    |   |        |         |    |        |      |       |   |        |
D2  |          |            |            |             |          |       |
D3  |  |   |  |  |   |   |  |  |   |   |  |  |  |   |   |  |   |   |  |   |
A1  | clip 1                  | clip 2                     | clip 3       |
A2  | clip 1                       | --  | clip 2      | clip 3           |

The time axis                                                              t


For the purposes of Annodex, data bitstreams are being regarded as a sequence of data packets that each have a timestamp representing the time at which the packet data starts and containing all the data required for the interval until the next packet starts. Thus, to insert a gap in a data bitstream (as in the annotation track 2 of the example above), a data packet has to be inserted explicitly annullating the data.

Data bitstreams generally contain the following information:

The setup information is inserted at the start of a data bitstream before any content data.

For the annotation bitstream, which represents a CMML file[15], the codec setup information consists of a CMML "head" tag containing annotations and meta data for the complete Annodex bitstream. It is thus inserted at the start of an annotation bitstream as setup information for that bitstream. The content data consists of the CMML "clip" tags without timing information. They contain information on the fragment of data between the clip's insertion time and the next clip on the same track (or the end of the document if none follows). CMML "clip" tags are encoded as described in the CMML specification[15].


4. Handling time in the Annodex format bitstream

Annodex format bitstreams inherently represent one timeline only, where the different data and the annotation bitstream can be thought of as content tracks on that timeline. All of these tracks relate to the same timeline which starts at a certain time point and ends when the last bitstream ends. An example bitstream can be seen in the following figure. It consists of an Annodex format bitstream that contains 4 media bitstreams and the annotation bitstream.

The following bitstream is a conceptual representation of the time intervals covered by the different logical bitstreams. In the flat representation these will be multiplexed such that the data packets of each of these bitstreams occur at the correct time.

t0                                                                   tn
|clip1  | clip 2 | clip 3               | clip 4                     |
annotation bitstream

| audio bitstream 1                         |
        | video bitstream 1                                          |
                 | audio bitstream 2                                 |
                        | video bitstream 2          |

The time point at which the Annodex format bitstream starts (t0 in the above diagram) is called the "timebase" and represents the playback time in seconds associated with the beginning of the Annodex bitstream. This start time may but does not have to be 0 - it can be any positive time offset.

Each one of the encapsulated media bitstreams and the annotation bitstream have their own temporal resolution at which they can provide data to cover the given timeline. This temporal resolution is usually given through the sampling rate of the particular bitstream. For example, a raw audio bitstream at CD quality is sampled with a sampling rate of 44100 Hz. A video bitstream may be sampled with a frame rate of 25 frames per second. This temporal resolution is stored in the "granulerate" field of the bos page of the bitstream.

The "granulerate" is used for the calculation of the time position for which a data packet of a media bitstream contains data. The "granulepos" field in an Ogg page when divided by the "granulerate" of that page's logical bitstream provides the time position that is reached in that bitstream after decoding all data packets finished on this page. E.g. if an audio bitstream has a granulerate of 44100 and starts at 0, then a granulepos of 88200 signifies that the bitstream has reached the second sec after the end of decoding this page's packets.

The annotation bitstream's "granulerate" can be chosen arbitrarily by the bitstream multiplexer. One option is to choose the least common multiple of the granulerates of all the media bitstreams to gain at least the resolution of the bitstreams. However, that resultion may not be enough compared to the one that the author of clips is asking for on insertion time. One solution is to accommodate for all possible time schemes of the clips. Thus, selecting the least common multiple of the resolutions of all the possible npt and smpte time schemes as the resolution of the annotation bitstream is another option.

The possible time schemes with their respecitve resolutions are:

To get to integer values, it is necessary to multiply all resolutions by 1000 and then take the least common multiple: lcm(1000000, 24000, 23976, 25000, 30000, 29970, 50000, 60000, 59940) = 2997000000. The "granulerate" would therefore be 2997000. This provides for a temporal resolution on the order of 10^-6, accommodating for a mixed use of all the above given time schemes with complete accuracy on the annotation bitstream.

The "granulepos" of the (set of) page(s) holding a "clip" element of the annotation stream has to signify the start time of that "clip" element. E.g. if the "granulerate" of the annotation bitstream is 1000, the "timebase" is 0, and a clip is to be inserted at npt=12.020, its "granulepos" will be 12020. Clips can be repeated in the Annodex format bitstream, which will be signified by having the same "track" attribute and the same page_sequence_number as the previous "clip" element.


5. Media encapsulation format

An Annodex format bitstream consists of XML markup in the annotation bitstream interleaved with the related media packet of the media bitstreams into a single bitstream.

It is not possible to use straight XML as encapsulation because XML cannot enclose binary data except encoded as Unicode. The use of Unicode would introduce too much overhead. Therefore, an encapsulation format that could handle binary bitstreams and textual pacetsk was required.

The following list gives a summary of the requirements for the Annodex format bitstream:

The Ogg encapsulation format version 0[11] was chosen as the encapsulation format for Annodex format bitstreams as it provides for all the requirements and has proven reliable and stable.

5.1 Media mapping for Ogg encapsulation

This section specifies the way the Ogg media encapsulation framework is used for creating Annodex format bitstreams. As such, knowledge of the Ogg bitstream format as specified in the Ogg RFC[11] is presumed. Please also refer to that document for descriptions of the terms used in this document. This section describes the specific media mapping that is used for Annodex format bitstreams.

Annodex format bitstreams consist of one or more time-continuous data bitstreams and an XML annotation bitstream concurrently interleaved (in Ogg terms: multiplexed) into an Ogg bitstream. Sequential multiplexing is allowed, but can only happen with complete Annodex format bitstreams.

As with any Ogg bitstream, the physical bitstream starts with the bos pages of all logical bitstreams, followed by the secondary header pages, followed by the data pages. Every Annodex format bitstream consists of at least two logical bitstreams: the Annodex media mapping bitstream and the annotation bitstream that represents a CMML[15] file. An Annodex physical bitstream starts with the bos pages of these two (in order), followed by the bos pages of any number of data bitstreams. Then all the secondary header pages of all the data bitstreams follow, including the secondary bos page(s) of the annotation bitstream containing the CMML "head" tag. Finally, all the data bitstreams and the annotation bitstream are multiplexed in Ogg pages in a time-synchronous fashion.

The next sections describe the different bos pages, which occur in the Annodex physical bitstream in the following order:

  1. Annodex media mapping bos
  2. annotation bitstream media mapping bos
  3. data bitstream(s) media mapping bos
  4. empty Annodex media mapping eos
  5. annotation bitstream secondary header page(s)
  6. data bitstream(s) secondary header page(s)
  7. annotation and data bitstream(s) content pages
  8. annotation and data bitstream(s) eos-s

5.2 The format of the Annodex media mapping bos

The Annodex media mapping bitstream consists only of one bos page which contains information for the complete Annodex physical bitstream. The bos page has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
   | Identifier 'Annodex\0'                                        |
   |                                                               |
   | Version major                 | Version minor                 |
   | Timebase numerator                                            |
   |                                                               |
   | Timebase denominator                                          |
   |                                                               |
   | UTC                                                           |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |

Fields with more than one byte length are encoded LSB (least significant byte) first.

The fields in the Annodex bos page have the following meaning:

  1. Identifier: a 8 Byte field that identifies this file to be of Annodex format. It contains the magic numbers:
    0x41 'A'
    0x6e 'n'
    0x6e 'n'
    0x6f 'o'
    0x64 'd'
    0x65 'e'
    0x78 'x'
    0x00 '\0'
  2. Version major: 2 Byte short integer number signifying the major version number of the Annodex format bitstream. This document specifies the major version 2.
  3. Version minor: 2 Byte short integer number signifying the minor version number of the Annodex format bitstream. This document specifies the minor version 0.
  4. Timebase numerator & denominator: 8 Byte integer number each. They represent together the timebase of the Annodex format bitstream given as a rational number. The denominator represents the temporal resolution at which the timebase is given. E.g. 5 on 1000 results in a timebase of 0.005 sec. This enables a very high temporal resolution without having to store floating point numbers.
  5. UTC: a 20 Byte string containing a UTC time in the form of YYYYMMDDTHHMMSS.sssZ. It associates a calendar date and a wall-clock time with the timebase. It is a sequence of 20 NUL Bytes if not in use, making this bos page constant length.

Please note: The possible temporal resolution of the timebase is on the order of 2^-64. However the time formats in use for media that are described in this document range from 1/24 to 1/60 for the different smpte formats and to 1/1000 for npt. Thus, this resolution is enough for any one of them. What's more, this resolution is expected to accommodate any future needs of time resolution for any other time format (and time-continuous sampled data).

5.3 The format of the media and annotation bitstream media mapping bos

The media and annotation bitstreams start each with one bos page containing information required for the decoding of the bitstream. After that, secondary header pages follow that contain information to set up the decoder for the bitstream and other stream-specific information. Then, the pages that contain the actual data follow.

The bos page of a media or annotation bitstream has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1| Byte
   | Identifier 'AnxData\0'                                        |
   |                                                               |
   | Granule rate numerator                                        |
   |                                                               |
   | Granule rate denominator                                      |
   |                                                               |
   | Number of secondary header pages                              |
   | Message header fields ...                                     |


Fields with more than one byte length are encoded LSB (least significant byte) first.

The fields in an AnxData bos page have the following meaning:

  1. Identifier: a 8 Byte field that identifies this file to be of a logical input bitstream with encoded information. It contains the magic numbers:
    0x41 'A'
    0x6e 'n'
    0x78 'x'
    0x44 'D'
    0x61 'a'
    0x74 't'
    0x61 'a'
    0x00 '\0'
  2. Granule rate numerator & denominater: 8 Byte integer number each. They represent the temporal resolution of the logical bitstream in Hz given as a rational number in the same way as the timebase attribute above.
  3. Number of secondary header pages: a 4 Byte integer number that contains the number of secondary header pages of that particular logical bitstream following after this bos page.
  4. Message header fields: header fields, following the generic Internet Message Format defined in RFC 2822[6]. Each header field consists of a name followed by a colon (":") and the field value. Field names are case-insensitive. The field value MAY be preceded by any amount of LWS, though a single SP is prefered. Header fields can be extended over multiple lines by preceding each extra line with at least one SP or HT.

Message header fields are considered protocol data, i.e. it is not expected to have human readable text in there. and are entirely encoded in UTF-8.

There is one mandatory Message header field for all of the logical bitstreams: the "Content-type" header field. For an application that is parsing the Annodex file, this field contains the MIME type and the character encoding of the data in the logical bitstream. E.g. for the annotation bitstream, this field will contain the value "Content-type: text/x-cmml; UTF-8" if the character set used is UTF-8. E.g. for a bitstream containing Ogg vorbis data the value is "Content-type: audio/x-vorbis". The Content-type message header field comes first of all the Message header fields such that it can be found at a fixed location in the AnxData header.


6. The decoding of Annodex format bitstreams to CMML

The decoding of an Annodex format bitstream to CMML is roughly inverse to the encoding an Annodex format bitstream from a CMML file. There are some special cases to take care of, therefore the decoding steps are outlined in order here.

The core of a CMML file can be created from the "head" tag taken from the secondary header page of the annotation bitstream, and from the sequence of "clip" tags extracted from the content of the annotation bitstream. A decoder MUST take care to reinsert the start time of each "clip" element into the "start" attribute of the respective CMML "clip" tag. The start time will be calculated from the Granule rate in the annotation bos page and the Granule pos given in the respective "clip" Ogg page.

If the Annodex bitstream has a non-zero timebase or a non-null utc time in the Annodex bos page, a "stream" tag MUST be created with these attribute values. That "stream" tag is empty by default. A ripping application MAY however extract all the data bitstreams out of the Annodex bitstream into files, and then reference these files in the "src" attribute of "import" tags.

Other attributes of the "import" tags MAY also be filled in from the logical bitstreams:

A stream tag will thus roughly be created like this:

<stream timebase="[Timebase]" utc="[UTC]">
  <import id="[ID]" granulerate="[Granulerate]" contenttype="[Content-type]"
          src="[stream1.mpg]" start="0"/>

If the annotation bitstream has Message header fields called "ID", "Content-Language", or "Content-Dir", the "cmml" tag of the decoded CMML file MUST use these field values in its "id", "lang", and "dir" attributes. This ensures that the default language setting of the annotation bitstream gets preserved:

<cmml id="[ID]" lang="[Content-Language]" dir="[Content-Dir]">

To restore the correct XML preamble for the CMML file, the charset part of the "Content-type" Message header field of the annotation bitstream MUST be extracted and used as value of the "encoding" attribute of the XML processing instruction. All the other fields of the XML preamble are fixed:

<?xml version="1.0" encoding="[Content-type]" standalone="yes"?>
<!DOCTYPE cmml SYSTEM "cmml.dtd">


7. MIME media type registration for 'application/annodex'

This section contains the registration information for the 'application/annodex' media type. While this media type is not approved by the IANA, 'application/x-annodex' may be used.


Subject: Registration of MIME media type application/annodex

MIME media type name: application

MIME subtype name: annodex

Required parameters: none

Optional parameters: none

Encoding Considerations: the Annodex enables encapsulation of any type of encoding format. The authoring software has to provide for the encoders, providing the MIME type (and potentially the charset for text-based formats) in the "Content-type" Message header field of each bitstream track. The client software can select an appropriate decoder based on this information.

Security considerations: see next section.

Interoperability considerations: the Annodex bitstream format is a free specification that is independent of any media encoding format. It is designed to provide interoperability with the existing World Wide Web. Its specification is not patented and can be implemented by third parties without patent considerations.

Additional information:

  • Magic numbers: "OggS" identifies an Ogg page, "Annodex" identifies an Ogg page with an Annodex format bitstreams, and "AnxData" signifies an Ogg page with media or annotation bitstream data.
  • File extension: .anx
  • Macintosh File Type Code: "ANDX"
  • Intended usage: COMMON
  • 7.1 URI addressing into Annodex files

    There are two ways of hyperlinking via URIs into Annodex files: via specification of a temporal interval or via specification of a clip. Both of these ways of addressing are supported for URI queries and URI fragments of Annodex files.

    7.1.1 Query parameters for use with the HTTP protocol server-side

    For the purposes of URI queries on Annodex files, it is assumed that the query string takes the format of a CGI query string. The Common Gateway Interface, or CGI, is a standard for external gateway programs to interface with information servers such as HTTP servers (see This query string is expected to be interpreted by the HTTP server to return a valid Annodex file that differs from the original Annodex file only by reducing it to the specified interval.

    Addressing of temporal intervals of Annodex files is possible through specification of temporal query intervals in URIs[14]. An example is the following URI:"npt:4" , which relates to a complete Annodex file composed from sample.anx by starting it at an offset of 4 seconds.

    Addressing of a clip is possible through specification of the clip's id attribute value. An example is the following URI:"dolphin" , which relates to the clip whose id attribute value is "dolphin". Note that id attribute values of all elements have to be unique throughout a XML file (and thus also throughout an Annodex file which represents a CMML file).

    7.1.2 Fragment identifiers for use with the HTTP protocol client-side

    For the purposes of URI fragment specifications on Annodex files, it is assumed that the fragment gets interpreted by the HTTP client after the retrieval action. The HTTP client is expected to restrict the usage of the resource to the specified interval.

    Addressing of temporal intervals of Annodex files is possible through specification of temporal fragments in URIs[14] An example is the following URI: . This then relates to starting the Annodex file at a 4 second offset. It may e.g. be useful to do a zoom into a retrieved Annodex resource.

    The values of the id attribute of the clip tags can be used for addressing media clips directly through fragment identifiers as in

    7.1.3 HTTP 'Accept' header field interpretation

    The Annodex and the CMML file that can be extracted from it are very tightly related to each other: the CMML file contains all annotation and indexing information including timebase and UTC time about the Annodex file. Therefore, receiving the CMML file instead of the Annodex file is like receiving all information about the bitstreams in the Annodex file except for the data bitstreams themselves.

    This situation can be taken advantage of with the "Accept" header of HTTP. When an Annodex file is requested from a HTTP server and the acceptable content types given in the "Accept" message header field contains "text/x-cmml" with a higher priority than "application/x-annodex", then the HTTP server SHOULD return the CMML file instead of the requested Annodex file itself. As is standard, the HTTP response will contain a "Content-type" field indicating what content was actually returned. A Web crawler of a search engine, e.g., can thus avoid extra network load and retrieve easier parsable information. It SHOULD set the "Accept" HTTP header to "Accept: text/x-cmml" for every requested Annodex URI.


    8. Security considerations

    Annodex format bitstreams contain several multiplexed binary media and one XML annotation bitstream. There is no generic encryption or signing mechanism provided for the complete bitstream or anyone of its parts. As the format of the encapsulated media bitstreams is not prescribed and is identified through the "Content-type" Message header field in that bitstream's bos page, it is possible to encrypt or sign that media bitstream and then mark it accordingly with a MIME type that signifies the encryption. It is up to the applications that use this bitstream to provide an appropriate codec to handle such bitstreams.

    As Annodex format bitstreams contain binary media bitstreams, it is possible to include executable content in them. This can be an issue with applications that decode these bitstreams, especially when they are used in a network scenario. Such applications have to ensure correct handling of manipulated bitstreams, of buffer overflow and the like.



    [1] World Wide Web Consortium, "Extensible Markup Language (XML) 1.0", W3C XML, October 2000.
    [2] World Wide Web Consortium, "HTML 4.01 Specification", W3C HTML, December 1999.
    [3] World Wide Web Consortium, "XHTML(TM) 1.0 The Extensible Hyper Text Markup Language", W3C XHTML, January 2000.
    [4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
    [5] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
    [6] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
    [7] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998.
    [8] Alvestrand, H., "Tags for the Identification of Languages", RFC 1766, March 1995.
    [9] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.
    [10] Whitehead, E. and M. Murata, "XML Media Types", RFC 2376, July 1998.
    [11] Pfeiffer, S., "The Ogg encapsulation format version 0", RFC 3533, May 2003.
    [12] The Society of Motion Picture and Television Engineers, "SMPTE STANDARD for Television, Audio and Film - Time and Control Code", ANSI 12M-1999, September 1999.
    [13] ISO, TC154., "Data elements and interchange formats -- Information interchange -- Representation of dates and times", ISO 8601, 2000.
    [14] Pfeiffer, S., Parker, C. and A. Pang, "Specifying time intervals in URI queries and fragments of time-based Web resources (BCP) (work in progress)", I-D draft-pfeiffer-temporal-fragments-02.txt, December 2003.
    [15] Pfeiffer, S., Parker, C. and A. Pang, "The Continuous Media Markup Language (CMML), Version 2.0 (work in progress)", I-D draft-pfeiffer-cmml-01.txt, December 2003.


    Authors' Addresses

      Silvia Pfeiffer
      Commonwealth Scientific and Industrial Research Organisation CSIRO, Australia
      Locked Bag 17
      North Ryde, NSW 2113
    Phone:  +61 2 9325 3141
      Conrad D. Parker
      Commonwealth Scientific and Industrial Research Organisation CSIRO, Australia
      Locked Bag 17
      North Ryde, NSW 2113
    Phone:  +61 2 9325 3133
      Andre T. Pang
      Commonwealth Scientific and Industrial Research Organisation CSIRO, Australia
      Locked Bag 17
      North Ryde, NSW 2113
    Phone:  +61 2 9325 3156


    Appendix A. Definitions of terms and abbreviations

    Clip element:
    XML data containing information on a fragment of a time-continuous bitstream.
    a subpart of a media document covering some temporal interval.
    XML tags and their content used to describe a media document.
    Annodex bitstream:
    encapsulated time-continuous bitstream with head and clip elements.
    the task of giving textual descriptions to fragments of media documents.
    the task of identifying index points for media documents or fragments thereof.
    the task of linking from one Web resource to another. If a link has an offset into the resource, this is sometimes called deep hyperlinking.
    head element:
    XML data containing information on an Annodexed media file.
    media packet:
    a block of digital data that represents a temporal subpart of a stream of continuous media. Media packets of one continuous media file do not overlap in time.
    a sequence of time-continuous data.


    Appendix B. Glossary of acronyms

    Continuous Media Markup Language.
    Document Type Declaration.
    eXtensible Markup Language.
    Continuous Media Web.
    World Wide Web.
    Unified Resource Identifier.


    Appendix C. Acknowledgements

    The authors greatly acknowledge the contributions of Zentaro Kavanagh, Andrew Nesbit and Simon Lai in developing this specification.


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