libogg-1.1.3.tar.gz

Network Working Group S. Pfeiffer Request for Comments: 3533 CSIRO Category: Informational May 2003 The Ogg Encapsulation Format Version 0 Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document describes the Ogg bitstream format version 0, which is a general, freely-available encapsulation format for media streams. It is able to encapsulate any kind and number of video and audio encoding formats as well as other data streams in a single bitstream. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [2]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Requirements for a generic encapsulation format . . . . . . . 3 4. The Ogg bitstream format . . . . . . . . . . . . . . . . . . . 3 5. The encapsulation process . . . . . . . . . . . . . . . . . . 6 6. The Ogg page format . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 A. Glossary of terms and abbreviations . . . . . . . . . . . . . 13 B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 14 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15 Pfeiffer Informational [Page 1]  RFC 3533 OGG May 2003 1. Introduction The Ogg bitstream format has been developed as a part of a larger project aimed at creating a set of components for the coding and decoding of multimedia content (codecs) which are to be freely available and freely re-implementable, both in software and in hardware for the computing community at large, including the Internet community. It is the intention of the Ogg developers represented by Xiph.Org that it be usable without intellectual property concerns. This document describes the Ogg bitstream format and how to use it to encapsulate one or several media bitstreams created by one or several encoders. The Ogg transport bitstream is designed to provide framing, error protection and seeking structure for higher-level codec streams that consist of raw, unencapsulated data packets, such as the Vorbis audio codec or the upcoming Tarkin and Theora video codecs. It is capable of interleaving different binary media and other time-continuous data streams that are prepared by an encoder as a sequence of data packets. Ogg provides enough information to properly separate data back into such encoder created data packets at the original packet boundaries without relying on decoding to find packet boundaries. Please note that the MIME type application/ogg has been registered with the IANA [1]. 2. Definitions For describing the Ogg encapsulation process, a set of terms will be used whose meaning needs to be well understood. Therefore, some of the most fundamental terms are defined now before we start with the description of the requirements for a generic media stream encapsulation format, the process of encapsulation, and the concrete format of the Ogg bitstream. See the Appendix for a more complete glossary. The result of an Ogg encapsulation is called the "Physical (Ogg) Bitstream". It encapsulates one or several encoder-created bitstreams, which are called "Logical Bitstreams". A logical bitstream, provided to the Ogg encapsulation process, has a structure, i.e., it is split up into a sequence of so-called "Packets". The packets are created by the encoder of that logical bitstream and represent meaningful entities for that encoder only (e.g., an uncompressed stream may use video frames as packets). They do not contain boundary information - strung together they appear to be streams of random bytes with no landmarks. Pfeiffer Informational [Page 2]  RFC 3533 OGG May 2003 Please note that the term "packet" is not used in this document to signify entities for transport over a network. 3. Requirements for a generic encapsulation format The design idea behind Ogg was to provide a generic, linear media transport format to enable both file-based storage and stream-based transmission of one or several interleaved media streams independent of the encoding format of the media data. Such an encapsulation format needs to provide: o framing for logical bitstreams. o interleaving of different logical bitstreams. o detection of corruption. o recapture after a parsing error. o position landmarks for direct random access of arbitrary positions in the bitstream. o streaming capability (i.e., no seeking is needed to build a 100% complete bitstream). o small overhead (i.e., use no more than approximately 1-2% of bitstream bandwidth for packet boundary marking, high-level framing, sync and seeking). o simplicity to enable fast parsing. o simple concatenation mechanism of several physical bitstreams. All of these design considerations have been taken into consideration for Ogg. Ogg supports framing and interleaving of logical bitstreams, seeking landmarks, detection of corruption, and stream resynchronisation after a parsing error with no more than approximately 1-2% overhead. It is a generic framework to perform encapsulation of time-continuous bitstreams. It does not know any specifics about the codec data that it encapsulates and is thus independent of any media codec. 4. The Ogg bitstream format A physical Ogg bitstream consists of multiple logical bitstreams interleaved in so-called "Pages". Whole pages are taken in order from multiple logical bitstreams multiplexed at the page level. The logical bitstreams are identified by a unique serial number in the Pfeiffer Informational [Page 3]  RFC 3533 OGG May 2003 header of each page of the physical bitstream. This unique serial number is created randomly and does not have any connection to the content or encoder of the logical bitstream it represents. Pages of all logical bitstreams are concurrently interleaved, but they need not be in a regular order - they are only required to be consecutive within the logical bitstream. Ogg demultiplexing reconstructs the original logical bitstreams from the physical bitstream by taking the pages in order from the physical bitstream and redirecting them into the appropriate logical decoding entity. Each Ogg page contains only one type of data as it belongs to one logical bitstream only. Pages are of variable size and have a page header containing encapsulation and error recovery information. Each logical bitstream in a physical Ogg bitstream starts with a special start page (bos=beginning of stream) and ends with a special page (eos=end of stream). The bos page contains information to uniquely identify the codec type and MAY contain information to set up the decoding process