Editing Theora (section)

==Technical details==
Theora is a [[variable bitrate|variable-bitrate]], [[discrete cosine transform|DCT]]-based video compression scheme. Like most common video codecs, Theora used [[chroma subsampling]], [[block (data storage)|block]]-based motion compensation and an 8-by-8 DCT block. Pixels are grouped into various structures, namely blocks, super blocks, and [[macroblocks]]. Theora supports intra-coded frames ("keyframes") and forward-predictive frames, but not [[B-frame|bi-predictive frames]] which are found in [[H.264]] and [[VC-1]]. Theora also does not support [[Interlaced video|interlacing]], or bit-depths larger than 8 bits per component.<ref name="theoraspec"/>

Theora video streams can be stored in any suitable [[container format (digital)|container format]], but they are most commonly found in the [[Ogg]] container with [[Vorbis]] or [[FLAC]] audio streams. This combination provided a completely open, royalty-free multimedia format. It can also be used with the [[Matroska]] container.<ref>{{cite web
  | publisher = Matroska | title = Matroska Codec Specs
  | url = https://www.matroska.org/technical/codec_specs.html | access-date =19 ¨May 2025
}}</ref>

The Theora video-compression format is compatible with the VP3 video-compression format, which consisted of a backward-compatible superset.<ref name="theora-license" /><ref name="FAQ-VP3">Xiph.org [https://theora.org/faq/#VP3 FAQ – Theora and VP3]. Retrieved 2 September 2009</ref> Theora is a superset of VP3, and VP3 streams (with some minor syntactic modifications) can be converted into Theora streams without recompression (but not vice versa).<ref name="FAQ-VP3" /> VP3 video compression can be decoded using Theora implementations, but Theora video compression usually cannot be decoded using old VP3 implementations.