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Bring in flac, ogg, vorbis
author Chris Cannam
date Tue, 19 Mar 2013 17:37:49 +0000
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+<!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;
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+
+h2 {
+  font-size: 1.2em;
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+
+h3 {
+  font-size: 1.1em;
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+  line-height: 1.4;
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+
+#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 (&trade;) of Xiph.Org.<br/>
+
+  These pages &copy; 1994 - 2005 Xiph.Org. All rights reserved.
+</div>
+
+</body>
+</html>