@@ -332,6 +365,20 @@ boundary information; strung together, the unframed packets form a logical bitstream of apparently random bytes with no internal landmarks. +

+ +

Packets of raw codec data are not typically internally framed. + When they are strung together into a stream without any container to + provide framing, they lose their individual boundaries. Seek and + capture are not possible within an unframed stream, and for many + codecs with variable length payloads and/or early-packet termination + (such as Vorbis), it may become impossible to recover the original + frame boundaries even if the stream is scanned linearly from + beginning to end. + +

Logical bitstream packets are grouped and framed into Ogg pages along with a unique stream serial number to produce a physical bitstream. An elementary stream is a @@ -341,6 +388,23 @@ be split and encoded across one or more pages. The page decode mechanism is designed to recognize, verify and handle single pages at a time from the overall bitstream. +

+ +

The primary purpose of a container is to provide framing for raw + packets, marking the packet boundaries so the exact packets can be + retrieved for decode later. The container also provides secondary + functions such as capture, timestamping, sequencing, stream + identification and so on. Not all of these functions are represented in the diagram. + +

In the Ogg container, pages do not necessarily contain + integer numbers of packets. Packets may span across page boundaries + or even multiple pages. This is necessary as pages have a maximum + possible size in order to provide capture guarantees, but packet + size is unbounded. +

+ +

Ogg Bitstream Framing specifies the page format of an Ogg bitstream, the packet coding process and elementary bitstreams in detail. @@ -455,8 +519,8 @@ scope of the physical bitstream.

consecutively. Such a physical bitstream obeys all the rules of both chained and multiplexed streams. Each link, when unchained, must stand on its own as a valid physical bitstream. Chained streams do -not mix; a new segment may not begin until all streams in the -preceding segment have terminated.

+not mix or interleave; a new segment may not begin until all streams +in the preceding segment have terminated.

Examples