The OGV file (.ogv)

OGV is the extension for video in the Ogg container from the Xiph.Org Foundation, the non-profit behind Vorbis, Opus and FLAC. The video inside is almost always Theora, Xiph's royalty-free video codec, with Vorbis audio. RFC 5334 set the extension and the media type video/ogg in 2008; before that, Ogg video files often used .ogg too.

Theora began as VP3, a codec from On2 Technologies. On2 released VP3 as open source in 2001 and handed it to Xiph in 2002; Xiph froze the Theora bitstream in 2004 and released libtheora 1.0 in November 2008. When HTML5 introduced the <video> element, Firefox (from version 3.5 in 2009), Chrome and Opera supported Ogg Theora as a format anyone could use without patent licences. Wikipedia and its sister sites used Ogg Theora with Vorbis for their video, with a player that only handled Ogg until WebM support arrived in 2012.

An Ogg file is pages all the way through. Each logical stream, one for video and one for audio, is cut into pages, and the pages of all streams are interleaved in time order. There's no index: players find their way with the granule position on each page, as in Ogg audio files.

• Headers first. Each stream starts with a page holding only its identification header, flagged BOS. All BOS pages come first, so a player knows every stream before any media arrives. Then come the comment and setup headers.
• Granule positions. For Theora, the number encodes the last keyframe and the frames since, using the keyframe granule shift from the header. For Vorbis it's the sample count. The container itself doesn't know about seconds.
• Duration and seeking. Without an index, a player finds the duration by reading the last page, and seeks by a bisection search through the file. Over the web, that means extra range requests, and slow or impossible seeking if the server doesn't support them.
• Skeleton. Some files add an Ogg Skeleton stream (fishead) with metadata about the other streams and, in later versions, keyframe indexes to speed up seeking. Most files don't have one.

Theora itself is a block-based codec of the same generation as MPEG-4 Part 2: it has keyframes and predicted frames but no B-frames, and only 8 bits per colour component. At the same bit rate it gives noticeably lower quality than H.264, VP9 or AV1.

Theora was one of the first video codecs on the open web, and it's now gone from all major browsers. Chrome announced its removal in October 2023, citing low use and the security risk of keeping a complex, little-used decoder; Theora was switched off by default from Chrome 120 and the code removed in Chrome 123, in early 2024. Edge, built on Chromium, followed. Firefox dropped Theora during 2024. Safari never supported it.

The Ogg container itself stays supported for audio, so an .ogv file may still play its Vorbis sound with no picture, or not at all. Sites that still need to play Theora can use ogv.js, a JavaScript and WebAssembly decoder, but converting the files is the lasting fix.

WebM is the natural successor: it's the same idea, royalty-free video for the web, and keeps Vorbis audio usable without re-encoding. Wikimedia Commons now prefers VP9 video in WebM for uploads, though it still accepts Ogg Theora files.

• Play it: VLC and mpv on Windows, macOS, Linux, Android and iOS play Ogg Theora. So does anything built on FFmpeg.
• Inspect it: ffprobe in.ogv shows the streams; ogginfo from vorbis-tools checks the page structure and reports errors.
• Edit it: convert first. Few editors import Theora, and those that do may struggle to seek without an index.

# OGV to WebM (VP9 + Opus): stays royalty-free
ffmpeg -i in.ogv -c:v libvpx-vp9 -crf 32 -b:v 0 -row-mt 1 -c:a libopus -b:a 96k out.webm

# OGV to MP4 (H.264 + AAC): plays on every device
ffmpeg -i in.ogv -c:v libx264 -crf 20 -pix_fmt yuv420p -c:a aac -movflags +faststart out.mp4

# keep the Vorbis audio as it is, in WebM
ffmpeg -i in.ogv -c:v libvpx-vp9 -crf 32 -b:v 0 -c:a copy out.webm

Re-encoding Theora loses a little quality, but Theora files are usually low-resolution and modest bit rate, so the new copy can be much smaller at the same quality. Keep the original if it's an archive copy.

• A page that used to show video now shows nothing: the browser removed Theora. Re-encode the file to WebM or MP4 and update the <video> source.
• Sound but no picture in a browser: the browser plays the Vorbis stream but can't decode Theora. Same fix.
• No duration, or the seek bar doesn't work: the player couldn't read the last page, often because the server doesn't support range requests, or the file was cut off before its end-of-stream pages.
• Won't open after trimming: Theora and Vorbis both need their three header packets. Cut with a tool that understands Ogg, such as FFmpeg, which writes the headers again.
• An .ogg file has a picture: older video files used .ogg before RFC 5334 introduced .ogv. Rename it, or just play it in VLC.

An OGV file holds only video, audio and tags; it can't run code. The real risk is the one Chrome gave for removing Theora: an old, rarely used decoder is a target for crafted files that exploit its bugs. If you still process Theora on a server, keep FFmpeg or libtheora updated, or convert files once and stop accepting the format. Tags are plain Vorbis comments, so check them for names or notes before publishing.