The development of the Ogg container format is led by the Xiph.Org Foundation, which is also responsible for development of FLAC, Vorbis and many other codecs. Ogg is actually only the container format for the Vorbis-encoded content.
Ogg container file format can contain audio, video, and text data at the same time. Ogg was designed to provide a free and unrestricted alternative to proprietary formats to efficiently store and stream multimedia content. Streaming capability is the key design feature: anything packed in an Ogg container can be streamed without any additional adjustments. This distinguishes Ogg from formats that are either only streamable in certain forms or are not live-streamable at all (such as MP4). Ogg streams can be bundled and concatenated without the need to adjust the individual stream.
Basic Details of Ogg
The Ogg file format is a container bitstream format. The container contains data, which in turn is compressed with different codecs. For compression, the text codec Writ, the speech data codec Speex, the audio codecs Vorbis or FLAC as well as the video codec Theora are usually used. This data is then grouped into logical bit streams (i.e. text, audio, video image) depending on its properties. Each logical bitstream is processed only with the appropriate codec. Several logical bit streams can be “stored” in a container. Also, several logical bitstreams of the same type (e.g., three logical video streams) can be contained in a container. These can also overlap during playback. To store or transmit the data over the network, these logical bit streams are converted into a physical bit stream (so-called data stream). This is then sent over the network. On the receiver side, a decoder recovers the various logical streams (e.g. text, audio, video image) from this data stream.
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The Internet Media Type application/ogg has been redefined and the Internet Media Types audio/ogg for audio data and video /ogg for video data have been added. File name extensions are .ogx for application/ogg, .ogv for video/ogg and .oga, .ogg and .spx for audio/ogg. On the other hand, the rarely used media type application/x-ogg dates back to earlier times, when the official type was not yet specified. Not part of the Ogg specs is the .ogm extension, which belongs to the Ogg-related (but not identical) Ogg Media format, which split off from Ogg to support additional video playback features.
- Audio (lossy)
- Speex: Audio codec for low-bitrate speech (~ 2.1–32 kbit/s per channel)
- Vorbis: handles music and speech for medium to high bitrates and also with variable bitrates (~16–500 kbit/s per channel)
- Opus: handles low- or high-bitrate speech or music (≈6-510 kbps per channel)
- Audio (lossless)
- Compressed: FLAC for lossless compressed audio
- Uncompressed: OggPCM. uncompressed music or speech in PCM audio, comparable to WAV
Ogg has now established itself in the IT sector, and in the audio sector, Ogg Vorbis is supported by many software and hardware products. The big breakthrough in private use has so far failed to materialize, but it is used in many web audio players due to the license-free nature of most browsers (with the exception of Apple’s Safari).
In this area, but also in the professional studio environment, the Vorbis successor format Opus is now becoming more and more popular. It offers far higher quality than Vorbis and works for both low bitrates (speech) and higher bitrates due to its hybrid architecture (two codec technologies in one codec).
Few of the FFmpeg developers critically evaluated the qualities of Ogg as a container format. Among other things, they argue that the file size overhead of 1% is at least eight times greater compared to the ISO MP4 format, and that Ogg is not suitable for applications that require low latency. As an alternative with supposedly better properties in this respect. However, the Ogg developer described its claims as largely unobjective and false.
