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844 lines
31 KiB
Text
844 lines
31 KiB
Text
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Network Working Group S. Pfeiffer
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Request for Comments: 3533 CSIRO
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Category: Informational May 2003
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The Ogg Encapsulation Format Version 0
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Status of this Memo
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This memo provides information for the Internet community. It does
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not specify an Internet standard of any kind. Distribution of this
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memo is unlimited.
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Copyright Notice
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Copyright (C) The Internet Society (2003). All Rights Reserved.
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Abstract
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This document describes the Ogg bitstream format version 0, which is
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a general, freely-available encapsulation format for media streams.
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It is able to encapsulate any kind and number of video and audio
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encoding formats as well as other data streams in a single bitstream.
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Terminology
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in BCP 14, RFC 2119 [2].
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Table of Contents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
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2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
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3. Requirements for a generic encapsulation format . . . . . . . 3
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4. The Ogg bitstream format . . . . . . . . . . . . . . . . . . . 3
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5. The encapsulation process . . . . . . . . . . . . . . . . . . 6
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6. The Ogg page format . . . . . . . . . . . . . . . . . . . . . 9
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
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8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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A. Glossary of terms and abbreviations . . . . . . . . . . . . . 13
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B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . 14
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Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15
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Pfeiffer Informational [Page 1]
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RFC 3533 OGG May 2003
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1. Introduction
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The Ogg bitstream format has been developed as a part of a larger
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project aimed at creating a set of components for the coding and
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decoding of multimedia content (codecs) which are to be freely
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available and freely re-implementable, both in software and in
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hardware for the computing community at large, including the Internet
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community. It is the intention of the Ogg developers represented by
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Xiph.Org that it be usable without intellectual property concerns.
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This document describes the Ogg bitstream format and how to use it to
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encapsulate one or several media bitstreams created by one or several
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encoders. The Ogg transport bitstream is designed to provide
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framing, error protection and seeking structure for higher-level
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codec streams that consist of raw, unencapsulated data packets, such
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as the Vorbis audio codec or the upcoming Tarkin and Theora video
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codecs. It is capable of interleaving different binary media and
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other time-continuous data streams that are prepared by an encoder as
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a sequence of data packets. Ogg provides enough information to
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properly separate data back into such encoder created data packets at
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the original packet boundaries without relying on decoding to find
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packet boundaries.
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Please note that the MIME type application/ogg has been registered
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with the IANA [1].
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2. Definitions
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For describing the Ogg encapsulation process, a set of terms will be
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used whose meaning needs to be well understood. Therefore, some of
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the most fundamental terms are defined now before we start with the
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description of the requirements for a generic media stream
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encapsulation format, the process of encapsulation, and the concrete
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format of the Ogg bitstream. See the Appendix for a more complete
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glossary.
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The result of an Ogg encapsulation is called the "Physical (Ogg)
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Bitstream". It encapsulates one or several encoder-created
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bitstreams, which are called "Logical Bitstreams". A logical
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bitstream, provided to the Ogg encapsulation process, has a
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structure, i.e., it is split up into a sequence of so-called
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"Packets". The packets are created by the encoder of that logical
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bitstream and represent meaningful entities for that encoder only
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(e.g., an uncompressed stream may use video frames as packets). They
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do not contain boundary information - strung together they appear to
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be streams of random bytes with no landmarks.
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Pfeiffer Informational [Page 2]
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RFC 3533 OGG May 2003
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Please note that the term "packet" is not used in this document to
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signify entities for transport over a network.
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3. Requirements for a generic encapsulation format
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The design idea behind Ogg was to provide a generic, linear media
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transport format to enable both file-based storage and stream-based
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transmission of one or several interleaved media streams independent
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of the encoding format of the media data. Such an encapsulation
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format needs to provide:
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o framing for logical bitstreams.
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o interleaving of different logical bitstreams.
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o detection of corruption.
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o recapture after a parsing error.
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o position landmarks for direct random access of arbitrary positions
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in the bitstream.
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o streaming capability (i.e., no seeking is needed to build a 100%
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complete bitstream).
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o small overhead (i.e., use no more than approximately 1-2% of
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bitstream bandwidth for packet boundary marking, high-level
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framing, sync and seeking).
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o simplicity to enable fast parsing.
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o simple concatenation mechanism of several physical bitstreams.
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All of these design considerations have been taken into consideration
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for Ogg. Ogg supports framing and interleaving of logical
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bitstreams, seeking landmarks, detection of corruption, and stream
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resynchronisation after a parsing error with no more than
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approximately 1-2% overhead. It is a generic framework to perform
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encapsulation of time-continuous bitstreams. It does not know any
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specifics about the codec data that it encapsulates and is thus
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independent of any media codec.
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4. The Ogg bitstream format
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A physical Ogg bitstream consists of multiple logical bitstreams
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interleaved in so-called "Pages". Whole pages are taken in order
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from multiple logical bitstreams multiplexed at the page level. The
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logical bitstreams are identified by a unique serial number in the
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Pfeiffer Informational [Page 3]
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RFC 3533 OGG May 2003
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header of each page of the physical bitstream. This unique serial
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number is created randomly and does not have any connection to the
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content or encoder of the logical bitstream it represents. Pages of
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all logical bitstreams are concurrently interleaved, but they need
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not be in a regular order - they are only required to be consecutive
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within the logical bitstream. Ogg demultiplexing reconstructs the
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original logical bitstreams from the physical bitstream by taking the
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pages in order from the physical bitstream and redirecting them into
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the appropriate logical decoding entity.
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Each Ogg page contains only one type of data as it belongs to one
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logical bitstream only. Pages are of variable size and have a page
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header containing encapsulation and error recovery information. Each
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logical bitstream in a physical Ogg bitstream starts with a special
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start page (bos=beginning of stream) and ends with a special page
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(eos=end of stream).
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The bos page contains information to uniquely identify the codec type
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and MAY contain information to set up the decoding process. The bos
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page SHOULD also contain information about the encoded media - for
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example, for audio, it should contain the sample rate and number of
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channels. By convention, the first bytes of the bos page contain
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magic data that uniquely identifies the required codec. It is the
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responsibility of anyone fielding a new codec to make sure it is
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possible to reliably distinguish his/her codec from all other codecs
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in use. There is no fixed way to detect the end of the codec-
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identifying marker. The format of the bos page is dependent on the
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codec and therefore MUST be given in the encapsulation specification
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of that logical bitstream type. Ogg also allows but does not require
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secondary header packets after the bos page for logical bitstreams
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and these must also precede any data packets in any logical
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bitstream. These subsequent header packets are framed into an
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integral number of pages, which will not contain any data packets.
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So, a physical bitstream begins with the bos pages of all logical
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bitstreams containing one initial header packet per page, followed by
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the subsidiary header packets of all streams, followed by pages
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containing data packets.
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The encapsulation specification for one or more logical bitstreams is
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called a "media mapping". An example for a media mapping is "Ogg
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Vorbis", which uses the Ogg framework to encapsulate Vorbis-encoded
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audio data for stream-based storage (such as files) and transport
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(such as TCP streams or pipes). Ogg Vorbis provides the name and
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revision of the Vorbis codec, the audio rate and the audio quality on
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the Ogg Vorbis bos page. It also uses two additional header pages
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per logical bitstream. The Ogg Vorbis bos page starts with the byte
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0x01, followed by "vorbis" (a total of 7 bytes of identifier).
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Pfeiffer Informational [Page 4]
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RFC 3533 OGG May 2003
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Ogg knows two types of multiplexing: concurrent multiplexing (so-
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called "Grouping") and sequential multiplexing (so-called
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"Chaining"). Grouping defines how to interleave several logical
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bitstreams page-wise in the same physical bitstream. Grouping is for
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example needed for interleaving a video stream with several
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synchronised audio tracks using different codecs in different logical
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bitstreams. Chaining on the other hand, is defined to provide a
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simple mechanism to concatenate physical Ogg bitstreams, as is often
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needed for streaming applications.
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In grouping, all bos pages of all logical bitstreams MUST appear
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together at the beginning of the Ogg bitstream. The media mapping
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specifies the order of the initial pages. For example, the grouping
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of a specific Ogg video and Ogg audio bitstream may specify that the
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physical bitstream MUST begin with the bos page of the logical video
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bitstream, followed by the bos page of the audio bitstream. Unlike
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bos pages, eos pages for the logical bitstreams need not all occur
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contiguously. Eos pages may be 'nil' pages, that is, pages
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containing no content but simply a page header with position
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information and the eos flag set in the page header. Each grouped
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logical bitstream MUST have a unique serial number within the scope
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of the physical bitstream.
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In chaining, complete logical bitstreams are concatenated. The
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bitstreams do not overlap, i.e., the eos page of a given logical
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bitstream is immediately followed by the bos page of the next. Each
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chained logical bitstream MUST have a unique serial number within the
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scope of the physical bitstream.
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It is possible to consecutively chain groups of concurrently
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multiplexed bitstreams. The groups, when unchained, MUST stand on
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their own as a valid concurrently multiplexed bitstream. The
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following diagram shows a schematic example of such a physical
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bitstream that obeys all the rules of both grouped and chained
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multiplexed bitstreams.
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physical bitstream with pages of
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different logical bitstreams grouped and chained
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-------------------------------------------------------------
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|*A*|*B*|*C*|A|A|C|B|A|B|#A#|C|...|B|C|#B#|#C#|*D*|D|...|#D#|
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-------------------------------------------------------------
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bos bos bos eos eos eos bos eos
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In this example, there are two chained physical bitstreams, the first
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of which is a grouped stream of three logical bitstreams A, B, and C.
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The second physical bitstream is chained after the end of the grouped
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bitstream, which ends after the last eos page of all its grouped
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logical bitstreams. As can be seen, grouped bitstreams begin
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Pfeiffer Informational [Page 5]
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RFC 3533 OGG May 2003
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together - all of the bos pages MUST appear before any data pages.
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It can also be seen that pages of concurrently multiplexed bitstreams
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need not conform to a regular order. And it can be seen that a
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grouped bitstream can end long before the other bitstreams in the
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group end.
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Ogg does not know any specifics about the codec data except that each
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logical bitstream belongs to a different codec, the data from the
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codec comes in order and has position markers (so-called "Granule
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positions"). Ogg does not have a concept of 'time': it only knows
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about sequentially increasing, unitless position markers. An
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application can only get temporal information through higher layers
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which have access to the codec APIs to assign and convert granule
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positions or time.
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A specific definition of a media mapping using Ogg may put further
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constraints on its specific use of the Ogg bitstream format. For
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example, a specific media mapping may require that all the eos pages
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for all grouped bitstreams need to appear in direct sequence. An
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example for a media mapping is the specification of "Ogg Vorbis".
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Another example is the upcoming "Ogg Theora" specification which
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encapsulates Theora-encoded video data and usually comes multiplexed
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with a Vorbis stream for an Ogg containing synchronised audio and
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video. As Ogg does not specify temporal relationships between the
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encapsulated concurrently multiplexed bitstreams, the temporal
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synchronisation between the audio and video stream will be specified
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in this media mapping. To enable streaming, pages from various
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logical bitstreams will typically be interleaved in chronological
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order.
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5. The encapsulation process
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The process of multiplexing different logical bitstreams happens at
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the level of pages as described above. The bitstreams provided by
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encoders are however handed over to Ogg as so-called "Packets" with
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packet boundaries dependent on the encoding format. The process of
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encapsulating packets into pages will be described now.
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From Ogg's perspective, packets can be of any arbitrary size. A
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specific media mapping will define how to group or break up packets
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from a specific media encoder. As Ogg pages have a maximum size of
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about 64 kBytes, sometimes a packet has to be distributed over
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several pages. To simplify that process, Ogg divides each packet
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into 255 byte long chunks plus a final shorter chunk. These chunks
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are called "Ogg Segments". They are only a logical construct and do
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not have a header for themselves.
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Pfeiffer Informational [Page 6]
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RFC 3533 OGG May 2003
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A group of contiguous segments is wrapped into a variable length page
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preceded by a header. A segment table in the page header tells about
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the "Lacing values" (sizes) of the segments included in the page. A
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flag in the page header tells whether a page contains a packet
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continued from a previous page. Note that a lacing value of 255
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implies that a second lacing value follows in the packet, and a value
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of less than 255 marks the end of the packet after that many
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additional bytes. A packet of 255 bytes (or a multiple of 255 bytes)
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is terminated by a lacing value of 0. Note also that a 'nil' (zero
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length) packet is not an error; it consists of nothing more than a
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lacing value of zero in the header.
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The encoding is optimized for speed and the expected case of the
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majority of packets being between 50 and 200 bytes large. This is a
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design justification rather than a recommendation. This encoding
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both avoids imposing a maximum packet size as well as imposing
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minimum overhead on small packets. In contrast, e.g., simply using
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two bytes at the head of every packet and having a max packet size of
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32 kBytes would always penalize small packets (< 255 bytes, the
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typical case) with twice the segmentation overhead. Using the lacing
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values as suggested, small packets see the minimum possible byte-
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aligned overhead (1 byte) and large packets (>512 bytes) see a fairly
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constant ~0.5% overhead on encoding space.
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Pfeiffer Informational [Page 7]
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|||
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|||
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RFC 3533 OGG May 2003
|
|||
|
|
|||
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|
|||
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The following diagram shows a schematic example of a media mapping
|
|||
|
using Ogg and grouped logical bitstreams:
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|||
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logical bitstream with packet boundaries
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-----------------------------------------------------------------
|
|||
|
> | packet_1 | packet_2 | packet_3 | <
|
|||
|
-----------------------------------------------------------------
|
|||
|
|
|||
|
|segmentation (logically only)
|
|||
|
v
|
|||
|
|
|||
|
packet_1 (5 segments) packet_2 (4 segs) p_3 (2 segs)
|
|||
|
------------------------------ -------------------- ------------
|
|||
|
.. |seg_1|seg_2|seg_3|seg_4|s_5 | |seg_1|seg_2|seg_3|| |seg_1|s_2 | ..
|
|||
|
------------------------------ -------------------- ------------
|
|||
|
|
|||
|
| page encapsulation
|
|||
|
v
|
|||
|
|
|||
|
page_1 (packet_1 data) page_2 (pket_1 data) page_3 (packet_2 data)
|
|||
|
------------------------ ---------------- ------------------------
|
|||
|
|H|------------------- | |H|----------- | |H|------------------- |
|
|||
|
|D||seg_1|seg_2|seg_3| | |D|seg_4|s_5 | | |D||seg_1|seg_2|seg_3| | ...
|
|||
|
|R|------------------- | |R|----------- | |R|------------------- |
|
|||
|
------------------------ ---------------- ------------------------
|
|||
|
|
|||
|
|
|
|||
|
pages of |
|
|||
|
other --------| |
|
|||
|
logical -------
|
|||
|
bitstreams | MUX |
|
|||
|
-------
|
|||
|
|
|
|||
|
v
|
|||
|
|
|||
|
page_1 page_2 page_3
|
|||
|
------ ------ ------- ----- -------
|
|||
|
... || | || | || | || | || | ...
|
|||
|
------ ------ ------- ----- -------
|
|||
|
physical Ogg bitstream
|
|||
|
|
|||
|
In this example we take a snapshot of the encapsulation process of
|
|||
|
one logical bitstream. We can see part of that bitstream's
|
|||
|
subdivision into packets as provided by the codec. The Ogg
|
|||
|
encapsulation process chops up the packets into segments. The
|
|||
|
packets in this example are rather large such that packet_1 is split
|
|||
|
into 5 segments - 4 segments with 255 bytes and a final smaller one.
|
|||
|
Packet_2 is split into 4 segments - 3 segments with 255 bytes and a
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 8]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
final very small one - and packet_3 is split into two segments. The
|
|||
|
encapsulation process then creates pages, which are quite small in
|
|||
|
this example. Page_1 consists of the first three segments of
|
|||
|
packet_1, page_2 contains the remaining 2 segments from packet_1, and
|
|||
|
page_3 contains the first three pages of packet_2. Finally, this
|
|||
|
logical bitstream is multiplexed into a physical Ogg bitstream with
|
|||
|
pages of other logical bitstreams.
|
|||
|
|
|||
|
6. The Ogg page format
|
|||
|
|
|||
|
A physical Ogg bitstream consists of a sequence of concatenated
|
|||
|
pages. Pages are of variable size, usually 4-8 kB, maximum 65307
|
|||
|
bytes. A page header contains all the information needed to
|
|||
|
demultiplex the logical bitstreams out of the physical bitstream and
|
|||
|
to perform basic error recovery and landmarks for seeking. Each page
|
|||
|
is a self-contained entity such that the page decode mechanism can
|
|||
|
recognize, verify, and handle single pages at a time without
|
|||
|
requiring the overall bitstream.
|
|||
|
|
|||
|
The Ogg page header 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
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| capture_pattern: Magic number for page start "OggS" | 0-3
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| version | header_type | granule_position | 4-7
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| | 8-11
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| | bitstream_serial_number | 12-15
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| | page_sequence_number | 16-19
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| | CRC_checksum | 20-23
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| |page_segments | segment_table | 24-27
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
| ... | 28-
|
|||
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
|||
|
|
|||
|
The LSb (least significant bit) comes first in the Bytes. Fields
|
|||
|
with more than one byte length are encoded LSB (least significant
|
|||
|
byte) first.
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 9]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
The fields in the page header have the following meaning:
|
|||
|
|
|||
|
1. capture_pattern: a 4 Byte field that signifies the beginning of a
|
|||
|
page. It contains the magic numbers:
|
|||
|
|
|||
|
0x4f 'O'
|
|||
|
|
|||
|
0x67 'g'
|
|||
|
|
|||
|
0x67 'g'
|
|||
|
|
|||
|
0x53 'S'
|
|||
|
|
|||
|
It helps a decoder to find the page boundaries and regain
|
|||
|
synchronisation after parsing a corrupted stream. Once the
|
|||
|
capture pattern is found, the decoder verifies page sync and
|
|||
|
integrity by computing and comparing the checksum.
|
|||
|
|
|||
|
2. stream_structure_version: 1 Byte signifying the version number of
|
|||
|
the Ogg file format used in this stream (this document specifies
|
|||
|
version 0).
|
|||
|
|
|||
|
3. header_type_flag: the bits in this 1 Byte field identify the
|
|||
|
specific type of this page.
|
|||
|
|
|||
|
* bit 0x01
|
|||
|
|
|||
|
set: page contains data of a packet continued from the previous
|
|||
|
page
|
|||
|
|
|||
|
unset: page contains a fresh packet
|
|||
|
|
|||
|
* bit 0x02
|
|||
|
|
|||
|
set: this is the first page of a logical bitstream (bos)
|
|||
|
|
|||
|
unset: this page is not a first page
|
|||
|
|
|||
|
* bit 0x04
|
|||
|
|
|||
|
set: this is the last page of a logical bitstream (eos)
|
|||
|
|
|||
|
unset: this page is not a last page
|
|||
|
|
|||
|
4. granule_position: an 8 Byte field containing position information.
|
|||
|
For example, for an audio stream, it MAY contain the total number
|
|||
|
of PCM samples encoded after including all frames finished on this
|
|||
|
page. For a video stream it MAY contain the total number of video
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 10]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
frames encoded after this page. This is a hint for the decoder
|
|||
|
and gives it some timing and position information. Its meaning is
|
|||
|
dependent on the codec for that logical bitstream and specified in
|
|||
|
a specific media mapping. A special value of -1 (in two's
|
|||
|
complement) indicates that no packets finish on this page.
|
|||
|
|
|||
|
5. bitstream_serial_number: a 4 Byte field containing the unique
|
|||
|
serial number by which the logical bitstream is identified.
|
|||
|
|
|||
|
6. page_sequence_number: a 4 Byte field containing the sequence
|
|||
|
number of the page so the decoder can identify page loss. This
|
|||
|
sequence number is increasing on each logical bitstream
|
|||
|
separately.
|
|||
|
|
|||
|
7. CRC_checksum: a 4 Byte field containing a 32 bit CRC checksum of
|
|||
|
the page (including header with zero CRC field and page content).
|
|||
|
The generator polynomial is 0x04c11db7.
|
|||
|
|
|||
|
8. number_page_segments: 1 Byte giving the number of segment entries
|
|||
|
encoded in the segment table.
|
|||
|
|
|||
|
9. segment_table: number_page_segments Bytes containing the lacing
|
|||
|
values of all segments in this page. Each Byte contains one
|
|||
|
lacing value.
|
|||
|
|
|||
|
The total header size in bytes is given by:
|
|||
|
header_size = number_page_segments + 27 [Byte]
|
|||
|
|
|||
|
The total page size in Bytes is given by:
|
|||
|
page_size = header_size + sum(lacing_values: 1..number_page_segments)
|
|||
|
[Byte]
|
|||
|
|
|||
|
7. Security Considerations
|
|||
|
|
|||
|
The Ogg encapsulation format is a container format and only
|
|||
|
encapsulates content (such as Vorbis-encoded audio). It does not
|
|||
|
provide for any generic encryption or signing of itself or its
|
|||
|
contained content bitstreams. However, it encapsulates any kind of
|
|||
|
content bitstream as long as there is a codec for it, and is thus
|
|||
|
able to contain encrypted and signed content data. It is also
|
|||
|
possible to add an external security mechanism that encrypts or signs
|
|||
|
an Ogg physical bitstream and thus provides content confidentiality
|
|||
|
and authenticity.
|
|||
|
|
|||
|
As Ogg encapsulates binary data, it is possible to include executable
|
|||
|
content in an Ogg bitstream. This can be an issue with applications
|
|||
|
that are implemented using the Ogg format, especially when Ogg is
|
|||
|
used for streaming or file transfer in a networking scenario. As
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 11]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
such, Ogg does not pose a threat there. However, an application
|
|||
|
decoding Ogg and its encapsulated content bitstreams has to ensure
|
|||
|
correct handling of manipulated bitstreams, of buffer overflows and
|
|||
|
the like.
|
|||
|
|
|||
|
8. References
|
|||
|
|
|||
|
[1] Walleij, L., "The application/ogg Media Type", RFC 3534, May
|
|||
|
2003.
|
|||
|
|
|||
|
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
|
|||
|
Levels", BCP 14, RFC 2119, March 1997.
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 12]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
Appendix A. Glossary of terms and abbreviations
|
|||
|
|
|||
|
bos page: The initial page (beginning of stream) of a logical
|
|||
|
bitstream which contains information to identify the codec type
|
|||
|
and other decoding-relevant information.
|
|||
|
|
|||
|
chaining (or sequential multiplexing): Concatenation of two or more
|
|||
|
complete physical Ogg bitstreams.
|
|||
|
|
|||
|
eos page: The final page (end of stream) of a logical bitstream.
|
|||
|
|
|||
|
granule position: An increasing position number for a specific
|
|||
|
logical bitstream stored in the page header. Its meaning is
|
|||
|
dependent on the codec for that logical bitstream and specified in
|
|||
|
a specific media mapping.
|
|||
|
|
|||
|
grouping (or concurrent multiplexing): Interleaving of pages of
|
|||
|
several logical bitstreams into one complete physical Ogg
|
|||
|
bitstream under the restriction that all bos pages of all grouped
|
|||
|
logical bitstreams MUST appear before any data pages.
|
|||
|
|
|||
|
lacing value: An entry in the segment table of a page header
|
|||
|
representing the size of the related segment.
|
|||
|
|
|||
|
logical bitstream: A sequence of bits being the result of an encoded
|
|||
|
media stream.
|
|||
|
|
|||
|
media mapping: A specific use of the Ogg encapsulation format
|
|||
|
together with a specific (set of) codec(s).
|
|||
|
|
|||
|
(Ogg) packet: A subpart of a logical bitstream that is created by the
|
|||
|
encoder for that bitstream and represents a meaningful entity for
|
|||
|
the encoder, but only a sequence of bits to the Ogg encapsulation.
|
|||
|
|
|||
|
(Ogg) page: A physical bitstream consists of a sequence of Ogg pages
|
|||
|
containing data of one logical bitstream only. It usually
|
|||
|
contains a group of contiguous segments of one packet only, but
|
|||
|
sometimes packets are too large and need to be split over several
|
|||
|
pages.
|
|||
|
|
|||
|
physical (Ogg) bitstream: The sequence of bits resulting from an Ogg
|
|||
|
encapsulation of one or several logical bitstreams. It consists
|
|||
|
of a sequence of pages from the logical bitstreams with the
|
|||
|
restriction that the pages of one logical bitstream MUST come in
|
|||
|
their correct temporal order.
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 13]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
(Ogg) segment: The Ogg encapsulation process splits each packet into
|
|||
|
chunks of 255 bytes plus a last fractional chunk of less than 255
|
|||
|
bytes. These chunks are called segments.
|
|||
|
|
|||
|
Appendix B. Acknowledgements
|
|||
|
|
|||
|
The author gratefully acknowledges the work that Christopher
|
|||
|
Montgomery and the Xiph.Org foundation have done in defining the Ogg
|
|||
|
multimedia project and as part of it the open file format described
|
|||
|
in this document. The author hopes that providing this document to
|
|||
|
the Internet community will help in promoting the Ogg multimedia
|
|||
|
project at http://www.xiph.org/. Many thanks also for the many
|
|||
|
technical and typo corrections that C. Montgomery and the Ogg
|
|||
|
community provided as feedback to this RFC.
|
|||
|
|
|||
|
Author's Address
|
|||
|
|
|||
|
Silvia Pfeiffer
|
|||
|
CSIRO, Australia
|
|||
|
Locked Bag 17
|
|||
|
North Ryde, NSW 2113
|
|||
|
Australia
|
|||
|
|
|||
|
Phone: +61 2 9325 3141
|
|||
|
EMail: Silvia.Pfeiffer@csiro.au
|
|||
|
URI: http://www.cmis.csiro.au/Silvia.Pfeiffer/
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 14]
|
|||
|
|
|||
|
RFC 3533 OGG May 2003
|
|||
|
|
|||
|
|
|||
|
Full Copyright Statement
|
|||
|
|
|||
|
Copyright (C) The Internet Society (2003). All Rights Reserved.
|
|||
|
|
|||
|
This document and translations of it may be copied and furnished to
|
|||
|
others, and derivative works that comment on or otherwise explain it
|
|||
|
or assist in its implementation may be prepared, copied, published
|
|||
|
and distributed, in whole or in part, without restriction of any
|
|||
|
kind, provided that the above copyright notice and this paragraph are
|
|||
|
included on all such copies and derivative works. However, this
|
|||
|
document itself may not be modified in any way, such as by removing
|
|||
|
the copyright notice or references to the Internet Society or other
|
|||
|
Internet organizations, except as needed for the purpose of
|
|||
|
developing Internet standards in which case the procedures for
|
|||
|
copyrights defined in the Internet Standards process must be
|
|||
|
followed, or as required to translate it into languages other than
|
|||
|
English.
|
|||
|
|
|||
|
The limited permissions granted above are perpetual and will not be
|
|||
|
revoked by the Internet Society or its successors or assigns.
|
|||
|
|
|||
|
This document and the information contained herein is provided on an
|
|||
|
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
|
|||
|
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
|
|||
|
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
|
|||
|
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
|
|||
|
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
|
|||
|
|
|||
|
Acknowledgement
|
|||
|
|
|||
|
Funding for the RFC Editor function is currently provided by the
|
|||
|
Internet Society.
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
|
|||
|
Pfeiffer Informational [Page 15]
|
|||
|
|