Ogg

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 Theora video codec.

Name

Ogg derives from "ogging", jargon from the computer game Netrek. Ogg is not an acronym and should not be mentioned as "OGG".

Design constraints for Ogg bitstreams

• True streaming; we must not need to seek to build a 100% complete bitstream.
• Use no more than approximately 1-2% of bitstream bandwidth for packet boundary marking, high-level framing, sync and seeking.
• Specification of absolute position within the original sample stream.
• Simple mechanism to ease limited editing, such as a simplified concatenation mechanism.
• Detection of corruption, recapture after error and direct, random access to data at arbitrary positions in the bitstream.

Projects using Ogg

Codecs

• CELT
• CMML
• FLAC (Ogg mapping)
• Kate
• PCM
• Skeleton
• Speex (Ogg mapping)
• Theora (Ogg mapping)
• Vorbis (Ogg mapping)
• Writ

Servers

• Annodex
• Icecast
• Metavid

Developer info

• GranulePosAndSeeking -- a discussion of the interpretation of granulepos, and the algorithm for seeking on Ogg files

Ogg page format

The LSb (least significant bit) comes first in the Bytes. Fields with more than one byte length are encoded LSB (least significant byte) first.

  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-
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Implementations

The Ogg encapsulation format can be handled with the following libraries:

• libogg: libogg svn (C, cross-platform) Low-level Ogg parsing and writing.
• liboggz: liboggz svn or liboggz (C, cross-platform) liboggz wraps libogg and provides features such as seeking.
• the Ogg Directshow filters: see illiminable (C++, Win32)
• HOgg (pure Haskell)
• JOrbis (pure Java) contains com.jcraft.jogg
• Mutagen (pure Python)

See also

• Oggless
• MIME Types and File Extensions

External links

• Ogg documentation
• Ogg RFC