libogg

libogg is a small, portable C library that implements the core Ogg bitstream container format. It provides the low-level interface used to assemble and parse Ogg streams, consisting of pages, segments, and packets. The library enables codecs and applications to package encoded data into a single stream or file while preserving frame boundaries, stream serial numbers, and sequence information. It is designed to be codec-agnostic and is commonly used as the container layer for codecs such as Vorbis and Theora, and for Opus when stored in an Ogg container.

The API revolves around a few opaque state structures: ogg_sync_state for input buffering and ogg_stream_state for output, plus ogg_page and ogg_packet structures that hold page and packet metadata. Typical usage includes initializing the sync or stream state, obtaining a buffer with ogg_sync_buffer and writing data with ogg_sync_wrote, extracting complete pages with ogg_pageout, and injecting packets with ogg_stream_packetin and producing pages with ogg_stream_pageout. The API handles CRC checks, page headers, and the sequence of pages for each logical bitstream.

libogg was developed by the Xiph.Org Foundation as part of the Ogg project and has been distributed with open-source multimedia tooling since the late 1990s. It emphasizes a minimal, portable interface suitable for embedding in applications and project libraries. The library is released under a permissive BSD-like license, allowing use in open- and closed-source software with minimal restrictions.

As the container layer of the Ogg ecosystem, libogg serves as a foundation for higher-level projects such as libvorbis and libtheora, and by Opus when stored in Ogg containers.