What Is an OGG File and How to Play It

Many media formats are available for users to choose from. The best-known ones are mostly proprietary. They're encumbered by patents, so it's difficult for third parties to create software that supports them. License fees cost money, and open-source developers often have no budget.

The designers of the OGG format created it as an open, patent-free container for audio and video streams. Anyone can create and distribute software to read and write OGG files without paying anything. The format is widely supported by both free and commercial software. It's primarily an audio format, with a video codec that is no longer supported.

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What is an OGG file? Media files generally have two separable aspects, and OGG follows this pattern. A file consists of a container that holds data with a particular encoding.

The container is the file's scaffolding. It includes a header, metadata, and a way to hold the encoded content. A container isn't limited to one encoding, though some pairings are so common they're expected.

The encoding is the way the audio or video is represented in bits. Sometimes you'll find encoded data without a container; for instance, MP3 files don't use a container except for an optional metadata block.

Encodings may be lossless or lossy. Lossless encodings represent the original analog signal at the full sampling rate and bit depth. Lossy ones eliminate low-order bits, using techniques that minimize the loss of quality. The advantage of lossy encodings is that the files are smaller.

The software that converts between analog signals and digital encodings is called a codec (coder-decoder).

OGG is a container format developed by the Xiph.Org foundation. The project dates back to 1993. It got going seriously when Fraunhofer announced it would charge license fees on all MP3 software. The aim was to create a media format that had a public specification which anyone could implement free of charge. Because of its open and widely supported nature, many options are now available for how to play .ogg files.

In principle, the OGG container can be used with many different encodings. You could have an OGG MP3 file, though no one ever does. If you have trouble playing an OGG file, it may be because it has an unusual encoding.

Generally, the container is used with encodings that are primarily intended for it. The two most important ones are Vorbis for audio and Theora for video.

Theora hasn't been supported for years. When people talk about the OGG file type, they mean OGG Vorbis unless they say otherwise. The extension for OGG Vorbis files can be either .ogg or .oga. OGG video files use the extension .ogv. If you have OGG Theora files, you should consider converting them before they become unusable.

The name "OGG Vorbis" will sound very familiar to fans of Terry Pratchett's Discworld novels. Vorbis is named after the villain in Pratchett's Small Gods. However, Xiph.Org insists that OGG isn't named after the witch Nanny OGG, who appears in many of the novels. It comes from an obscure jargon term.

An OGG file consists of one or more "pages." Each page starts with the ASCII letters "OGGS" followed by the version number. If a player sees these bytes at the start of a file, it can be reasonably confident it's dealing with an OGG container. It provides boundary marking and error checking for the stream data.

The format is designed to support true streaming. It isn't necessary to load the entire file before playing it. This avoids memory limitations on playback of large files. A stream can go on for hours, and only the part currently playing needs to be loaded in memory.

Metadata is important to a media file. It consists of information on the name of the work being played, its creator, copyright, performers, and so on. OGG supports several metadata formats, but the most common one is the VorbisComment format. VorbisComments consist of key-value pairs, such as "TITLE=Hallelujah," and their size is virtually unlimited (16 exabytes).

In working with OGG, you may run into the MOGG format. It stands for "Multitrack OGG" and is a package for holding multiple OGG files to be treated as tracks. It's not very common.

Vorbis is the usual encoding for OGG audio files. It's a lossy encoding. As previously mentioned, this means that it removes some information to get better compression. Whether the loss is noticeable depends on your ears and the amount of compression used.

A Vorbis stream can carry up to 255 channels. It can support mono, stereo, quadraphonic, subwoofer channels, and a lot more.

Unlike MP3 and some other formats, Vorbis uses a variable-bitrate encoding. The creator of a file can set it from -2 (or -1, depending on the software) to 10. A quality setting of 0 is roughly 64 Kb/second and is comparable to a phone conversation. Setting the quality to 10 will take up about 500 Kb/second. Vorbis gives better quality than MP3 for the same amount of compression. The encoding depth of samples is usually 16 bits, though it can be more.

The Vorbis 1 bitstream format has been frozen since the year 2000. Any files created in the future will play on today's players. There could be a Vorbis 2 someday, though there are no signs of one yet.

Sometimes file creators will use OGG with the FLAC encoding to generate lossless files. Software that plays OGG Vorbis may or may not be able to play these files.