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diff --git a/doc/vorbis.html b/doc/vorbis.html new file mode 100644 index 0000000..66df2f4 --- /dev/null +++ b/doc/vorbis.html @@ -0,0 +1,234 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html> +<head> + +<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-15"/> +<title>Ogg Vorbis Documentation</title> + +<style type="text/css"> +body { + margin: 0 18px 0 18px; + padding-bottom: 30px; + font-family: Verdana, Arial, Helvetica, sans-serif; + color: #333333; + font-size: .8em; +} + +a { + color: #3366cc; +} + +img { + border: 0; +} + +#xiphlogo { + margin: 30px 0 16px 0; +} + +#content p { + line-height: 1.4; +} + +h1, h1 a, h2, h2 a, h3, h3 a { + font-weight: bold; + color: #ff9900; + margin: 1.3em 0 8px 0; +} + +h1 { + font-size: 1.3em; +} + +h2 { + font-size: 1.2em; +} + +h3 { + font-size: 1.1em; +} + +li { + line-height: 1.4; +} + +#copyright { + margin-top: 30px; + line-height: 1.5em; + text-align: center; + font-size: .8em; + color: #888888; + clear: both; +} +</style> + +</head> + +<body> + +<div id="xiphlogo"> + <a href="http://www.xiph.org/"><img src="fish_xiph_org.png" alt="Fish Logo and Xiph.org"/></a> +</div> + +<h1>Ogg Vorbis encoding format documentation</h1> + +<p><img src="wait.png" alt="wait"/>As of writing, not all the below document +links are live. They will be populated as we complete the documents.</p> + +<h2>Documents</h2> + +<ul> +<li><a href="packet.html">Vorbis packet structure</a></li> +<li><a href="envelope.html">Temporal envelope shaping and blocksize</a></li> +<li><a href="mdct.html">Time domain segmentation and MDCT transform</a></li> +<li><a href="resolution.html">The resolution floor</a></li> +<li><a href="residuals.html">MDCT-domain fine structure</a></li> +</ul> + +<ul> +<li><a href="probmodel.html">The Vorbis probability model</a></li> +<li><a href="bitpack.html">The Vorbis bitpacker</a></li> +</ul> + +<ul> +<li><a href="oggstream.html">Ogg bitstream overview</a></li> +<li><a href="framing.html">Ogg logical bitstream and framing spec</a></li> +<li><a href="vorbis-stream.html">Vorbis packet->Ogg bitstream mapping</a></li> +</ul> + +<ul> +<li><a href="programming.html">Programming with libvorbis</a></li> +</ul> + +<h2>Description</h2> + +<p>Ogg Vorbis is a general purpose compressed audio format +for high quality (44.1-48.0kHz, 16+ bit, polyphonic) audio and music +at moderate fixed and variable bitrates (40-80 kb/s/channel). This +places Vorbis in the same class as audio representations including +MPEG-1 audio layer 3, MPEG-4 audio (AAC and TwinVQ), and PAC.</p> + +<p>Vorbis is the first of a planned family of Ogg multimedia coding +formats being developed as part of the Xiph.org Foundation's Ogg multimedia +project. See <a href="http://www.xiph.org/">http://www.xiph.org/</a> +for more information.</p> + +<h2>Vorbis technical documents</h2> + +<p>A Vorbis encoder takes in overlapping (but contiguous) short-time +segments of audio data. The encoder analyzes the content of the audio +to determine an optimal compact representation; this phase of encoding +is known as <em>analysis</em>. For each short-time block of sound, +the encoder then packs an efficient representation of the signal, as +determined by analysis, into a raw packet much smaller than the size +required by the original signal; this phase is <em>coding</em>. +Lastly, in a streaming environment, the raw packets are then +structured into a continuous stream of octets; this last phase is +<em>streaming</em>. Note that the stream of octets is referred to both +as a 'byte-' and 'bit-'stream; the latter usage is acceptible as the +stream of octets is a physical representation of a true logical +bit-by-bit stream.</p> + +<p>A Vorbis decoder performs a mirror image process of extracting the +original sequence of raw packets from an Ogg stream (<em>stream +decomposition</em>), reconstructing the signal representation from the +raw data in the packet (<em>decoding</em>) and them reconstituting an +audio signal from the decoded representation (<em>synthesis</em>).</p> + +<p>The <a href="programming.html">Programming with libvorbis</a> +documents discuss use of the reference Vorbis codec library +(libvorbis) produced by the Xiph.org Foundation.</p> + +<p>The data representations and algorithms necessary at each step to +encode and decode Ogg Vorbis bitstreams are described by the below +documents in sufficient detail to construct a complete Vorbis codec. +Note that at the time of writing, Vorbis is still in a 'Request For +Comments' stage of development; despite being in advanced stages of +development, input from the multimedia community is welcome.</p> + +<h3>Vorbis analysis and synthesis</h3> + +<p>Analysis begins by seperating an input audio stream into individual, +overlapping short-time segments of audio data. These segments are +then transformed into an alternate representation, seeking to +represent the original signal in a more efficient form that codes into +a smaller number of bytes. The analysis and transformation stage is +the most complex element of producing a Vorbis bitstream.</p> + +<p>The corresponding synthesis step in the decoder is simpler; there is +no analysis to perform, merely a mechanical, deterministic +reconstruction of the original audio data from the transform-domain +representation.</p> + +<ul> +<li><a href="packet.html">Vorbis packet structure</a>: +Describes the basic analysis components necessary to produce Vorbis +packets and the structure of the packet itself.</li> +<li><a href="envelope.html">Temporal envelope shaping and blocksize</a>: +Use of temporal envelope shaping and variable blocksize to minimize +time-domain energy leakage during wide dynamic range and spectral energy +swings. Also discusses time-related principles of psychoacoustics.</li> +<li><a href="mdct.html">Time domain segmentation and MDCT transform</a>: +Division of time domain data into individual overlapped, windowed +short-time vectors and transformation using the MDCT</li> +<li><a href="resolution.html">The resolution floor</a>: Use of frequency +doamin psychoacoustics, and the MDCT-domain noise, masking and resolution +floors</li> +<li><a href="residuals.html">MDCT-domain fine structure</a>: Production, +quantization and massaging of MDCT-spectrum fine structure</li> +</ul> + +<h3>Vorbis coding and decoding</h3> + +<p>Coding and decoding converts the transform-domain representation of +the original audio produced by analysis to and from a bitwise packed +raw data packet. Coding and decoding consist of two logically +orthogonal concepts, <em>back-end coding</em> and <em>bitpacking</em>.</p> + +<p><em>Back-end coding</em> uses a probability model to represent the raw numbers +of the audio representation in as few physical bits as possible; +familiar examples of back-end coding include Huffman coding and Vector +Quantization.</p> + +<p><em>Bitpacking</em> arranges the variable sized words of the back-end +coding into a vector of octets without wasting space. The octets +produced by coding a single short-time audio segment is one raw Vorbis +packet.</p> + +<ul> +<li><a href="probmodel.html">The Vorbis probability model</a></li> +<li><a href="bitpack.html">The Vorbis bitpacker</a>: Arrangement of +variable bit-length words into an octet-aligned packet.</li> +</ul> + +<h3>Vorbis streaming and stream decomposition</h3> + +<p>Vorbis packets contain the raw, bitwise-compressed representation of a +snippet of audio. These packets contain no structure and cannot be +strung together directly into a stream; for streamed transmission and +storage, Vorbis packets are encoded into an Ogg bitstream.</p> + +<ul> +<li><a href="oggstream.html">Ogg bitstream overview</a>: High-level +description of Ogg logical bitstreams, how logical bitstreams +(of mixed media types) can be combined into physical bitstreams, and +restrictions on logical-to-physical mapping. Note that this document is +not specific only to Ogg Vorbis.</li> +<li><a href="framing.html">Ogg logical bitstream and framing +spec</a>: Low level, complete specification of Ogg logical +bitstream pages. Note that this document is not specific only to Ogg +Vorbis.</li> +<li><a href="vorbis-stream.html">Vorbis bitstream mapping</a>: +Specifically describes mapping Vorbis data into an +Ogg physical bitstream.</li> +</ul> + +<div id="copyright"> + The Xiph Fish Logo is a + trademark (™) of Xiph.Org.<br/> + + These pages © 1994 - 2005 Xiph.Org. All rights reserved. +</div> + +</body> +</html> |