-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">\r
-<html>\r
-<head>\r
-\r
-<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-15"/>\r
-<title>Ogg Vorbis Documentation</title>\r
-\r
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-#xiphlogo {\r
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- line-height: 1.4;\r
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- font-weight: bold;\r
- color: #ff9900;\r
- margin: 1.3em 0 8px 0;\r
-}\r
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- font-size: 1.3em;\r
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- font-size: 1.1em;\r
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- line-height: 1.4;\r
-}\r
-\r
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- margin-top: 30px;\r
- line-height: 1.5em;\r
- text-align: center;\r
- font-size: .8em;\r
- color: #888888;\r
- clear: both;\r
-}\r
-</style>\r
-\r
-</head>\r
-\r
-<body>\r
-\r
-<div id="xiphlogo">\r
- <a href="http://www.xiph.org/"><img src="fish_xiph_org.png" alt="Fish Logo and Xiph.org"/></a>\r
-</div>\r
-\r
-<h1>Programming with Xiph.org <tt>libvorbis</tt></h1>\r
-\r
-<h2>Description</h2> \r
-\r
-<p>Libvorbis is the Xiph.org Foundation's portable Ogg Vorbis CODEC\r
-implemented as a programmatic library. Libvorbis provides primitives\r
-to handle framing and manipulation of Ogg bitstreams (used by the\r
-Vorbis for streaming), a full analysis (encoding) interface as well as\r
-packet decoding and synthesis for playback.</p>\r
-\r
-<p>The libvorbis library does not provide any system interface; a\r
-full-featured demonstration player included with the library\r
-distribtion provides example code for a variety of system interfaces\r
-as well as a working example of using libvorbis in production code.</p>\r
-\r
-<h2>Encoding Overview</h2>\r
-\r
-<h2>Decoding Overview</h2>\r
-\r
-<p>Decoding a bitstream with libvorbis follows roughly the following\r
-steps:</p>\r
-\r
-<ol>\r
-<li>Frame the incoming bitstream into pages</li>\r
-<li>Sort the pages by logical bitstream and buffer then into logical streams</li>\r
-<li>Decompose the logical streams into raw packets</li>\r
-<li>Reconstruct segments of the original data from each packet</li>\r
-<li>Glue the reconstructed segments back into a decoded stream</li>\r
-</ol>\r
-\r
-<h3>Framing</h3>\r
-\r
-<p>An Ogg bitstream is logically arranged into pages, but to decode\r
-the pages, we have to find them first. The raw bitstream is first fed\r
-into an <tt>ogg_sync_state</tt> buffer using <tt>ogg_sync_buffer()</tt>\r
-and <tt>ogg_sync_wrote()</tt>. After each block we submit to the sync\r
-buffer, we should check to see if we can frame and extract a complete\r
-page or pages using <tt>ogg_sync_pageout()</tt>. Extra pages are\r
-buffered; allowing them to build up in the <tt>ogg_sync_state</tt>\r
-buffer will eventually exhaust memory.</p>\r
-\r
-<p>The Ogg pages returned from <tt>ogg_sync_pageout</tt> need not be\r
-decoded further to be used as landmarks in seeking; seeking can be\r
-either a rough process of simply jumping to approximately intuited\r
-portions of the bitstream, or it can be a precise bisection process\r
-that captures pages and inspects data position. When seeking,\r
-however, sequential multiplexing (chaining) must be accounted for;\r
-beginning play in a new logical bitstream requires initializing a\r
-synthesis engine with the headers from that bitstream. Vorbis\r
-bitstreams do not make use of concurent multiplexing (grouping).</p>\r
-\r
-<h3>Sorting</h3>\r
-\r
-<p>The pages produced by <tt>ogg_sync_pageout</tt> are then sorted by\r
-serial number to seperate logical bitstreams. Initialize logical\r
-bitstream buffers (<tt>og_stream_state</tt>) using\r
-<tt>ogg_stream_init()</tt>. Pages are submitted to the matching\r
-logical bitstream buffer using <tt>ogg_stream_pagein</tt>; the serial\r
-number of the page and the stream buffer must match, or the page will\r
-be rejected. A page submitted out of sequence will simply be noted,\r
-and in the course of outputting packets, the hole will be flagged\r
-(<tt>ogg_sync_pageout</tt> and <tt>ogg_stream_packetout</tt> will\r
-return a negative value at positions where they had to recapture the\r
-stream).</p>\r
-\r
-<h3>Extracting packets</h3>\r
-\r
-<p>After submitting page[s] to a logical stream, read available packets\r
-using <tt>ogg_stream_packetout</tt>.</p>\r
-\r
-<h3>Decoding packets</h3>\r
-\r
-<h3>Reassembling data segments</h3>\r
-\r
-<h2>Ogg Bitstream Manipulation Structures</h2>\r
-\r
-<p>Two of the Ogg bitstream data structures are intended to be\r
-transparent to the developer; the fields should be used directly.</p>\r
-\r
-<h3>ogg_packet</h3>\r
-\r
-<pre>\r
-typedef struct {\r
- unsigned char *packet;\r
- long bytes;\r
- long b_o_s;\r
- long e_o_s;\r
-\r
- size64 granulepos;\r
-\r
-} ogg_packet;\r
-</pre>\r
-\r
-<dl>\r
-<dt>packet:</dt>\r
-<dd>a pointer to the byte data of the raw packet</dd>\r
-<dt>bytes:</dt>\r
-<dd>the size of the packet' raw data</dd>\r
-<dt>b_o_s:</dt>\r
-<dd>beginning of stream; nonzero if this is the first packet of \r
- the logical bitstream</dd>\r
-<dt>e_o_s:</dt>\r
-<dd>end of stream; nonzero if this is the last packet of the \r
- logical bitstream</dd>\r
-<dt>granulepos:</dt>\r
-<dd>the absolute position of this packet in the original \r
- uncompressed data stream.</dd>\r
-</dl>\r
-\r
-<h4>encoding notes</h4>\r
-\r
-<p>The encoder is responsible for setting all of\r
-the fields of the packet to appropriate values before submission to\r
-<tt>ogg_stream_packetin()</tt>; however, it is noted that the value in\r
-<tt>b_o_s</tt> is ignored; the first page produced from a given\r
-<tt>ogg_stream_state</tt> structure will be stamped as the initial\r
-page. <tt>e_o_s</tt>, however, must be set; this is the means by\r
-which the stream encoding primitives handle end of stream and cleanup.</p>\r
-\r
-<h4>decoding notes</h4>\r
-\r
-<p><tt>ogg_stream_packetout()</tt> sets the fields\r
-to appropriate values. Note that granulepos will be >= 0 only in the\r
-case that the given packet actually represents that position (ie, only\r
-the last packet completed on any page will have a meaningful\r
-<tt>granulepos</tt>). Intervening frames will see <tt>granulepos</tt> set\r
-to -1.</p>\r
-\r
-<h3>ogg_page</h3>\r
-\r
-<pre>\r
-typedef struct {\r
- unsigned char *header;\r
- long header_len;\r
- unsigned char *body;\r
- long body_len;\r
-} ogg_page;\r
-</pre>\r
-\r
-<dl>\r
-<dt>header:</dt>\r
-<dd>pointer to the page header data</dd>\r
-<dt>header_len:</dt>\r
-<dd>length of the page header in bytes</dd>\r
-<dt>body:</dt>\r
-<dd>pointer to the page body</dd>\r
-<dt>body_len:</dt>\r
-<dd>length of the page body</dd>\r
-</dl>\r
-\r
-<p>Note that although the <tt>header</tt> and <tt>body</tt> pointers do\r
-not necessarily point into a single contiguous page vector, the page\r
-body must immediately follow the header in the bitstream.</p>\r
-\r
-<h2>Ogg Bitstream Manipulation Functions</h2>\r
-\r
-<h3>\r
-int ogg_page_bos(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the 'beginning of stream' flag for the given Ogg page. The\r
-beginning of stream flag is set on the initial page of a logical\r
-bitstream.</p>\r
-\r
-<p>Zero indicates the flag is cleared (this is not the initial page of a\r
-logical bitstream). Nonzero indicates the flag is set (this is the\r
-initial page of a logical bitstream).</p>\r
-\r
-<h3>\r
-int ogg_page_continued(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the 'packet continued' flag for the given Ogg page. The packet\r
-continued flag indicates whether or not the body data of this page\r
-begins with packet continued from a preceeding page.</p>\r
-\r
-<p>Zero (unset) indicates that the body data begins with a new packet.\r
-Nonzero (set) indicates that the first packet data on the page is a\r
-continuation from the preceeding page.</p>\r
-\r
-<h3>\r
-int ogg_page_eos(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the 'end of stream' flag for a give Ogg page. The end of page\r
-flag is set on the last (terminal) page of a logical bitstream.</p>\r
-\r
-<p>Zero (unset) indicates that this is not the last page of a logical\r
-bitstream. Nonzero (set) indicates that this is the last page of a\r
-logical bitstream and that no addiitonal pages belonging to this\r
-bitstream may follow.</p>\r
-\r
-<h3>\r
-size64 ogg_page_granulepos(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the position of this page as an absolute position within the\r
-original uncompressed data. The position, as returned, is 'frames\r
-encoded to date up to and including the last whole packet on this\r
-page'. Partial packets begun on this page but continued to the\r
-following page are not included. If no packet ends on this page, the\r
-frame position value will be equal to the frame position value of the\r
-preceeding page. If none of the original uncompressed data is yet\r
-represented in the logical bitstream (for example, the first page of a\r
-bitstream consists only of a header packet; this packet encodes only\r
-metadata), the value shall be zero.</p>\r
-\r
-<p>The units of the framenumber are determined by media mapping. A\r
-vorbis audio bitstream, for example, defines one frame to be the\r
-channel values from a single sampling period (eg, a 16 bit stereo\r
-bitstream consists of two samples of two bytes for a total of four\r
-bytes, thus a frame would be four bytes). A video stream defines one\r
-frame to be a single frame of video.</p>\r
-\r
-<h3>\r
-int ogg_page_pageno(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the sequential page number of the given Ogg page. The first\r
-page in a logical bitstream is numbered zero; following pages are\r
-numbered in increasing monotonic order.</p>\r
-\r
-<h3>\r
-int ogg_page_serialno(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the serial number of the given Ogg page. The serial number is\r
-used as a handle to distinguish various logical bitstreams in a\r
-physical Ogg bitstresm. Every logical bitstream within a\r
-physical bitstream must use a unique (within the scope of the physical\r
-bitstream) serial number, which is stamped on all bitstream pages.</p>\r
-\r
-<h3>\r
-int ogg_page_version(ogg_page *og);\r
-</h3>\r
-\r
-<p>Returns the revision of the Ogg bitstream structure of the given page.\r
-Currently, the only permitted number is zero. Later revisions of the\r
-bitstream spec will increment this version should any changes be\r
-incompatable.</p>\r
-\r
-<h3>\r
-int ogg_stream_clear(ogg_stream_state *os);\r
-</h3>\r
-\r
-<p>Clears and deallocates the internal storage of the given Ogg stream.\r
-After clearing, the stream structure is not initialized for use;\r
-<tt>ogg_stream_init</tt> must be called to reinitialize for use.\r
-Use <tt>ogg_stream_reset</tt> to reset the stream state\r
-to a fresh, intiialized state.</p>\r
-\r
-<p><tt>ogg_stream_clear</tt> does not call <tt>free()</tt> on the pointer\r
-<tt>os</tt>, allowing use of this call on stream structures in static\r
-or automatic storage. <tt>ogg_stream_destroy</tt>is a complimentary\r
-function that frees the pointer as well.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure. This function always\r
-succeeds.</p>\r
-\r
-<h3>\r
-int ogg_stream_destroy(ogg_stream_state *os);\r
-</h3>\r
-\r
-<p>Clears and deallocates the internal storage of the given Ogg stream,\r
-then frees the storage associated with the pointer <tt>os</tt>.</p>\r
-\r
-<p><tt>ogg_stream_clear</tt> does not call <tt>free()</tt> on the pointer\r
-<tt>os</tt>, allowing use of that call on stream structures in static\r
-or automatic storage.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure. This function always\r
-succeeds.</p>\r
-\r
-<h3>\r
-int ogg_stream_init(ogg_stream_state *os,int serialno);\r
-</h3>\r
-\r
-<p>Initialize the storage associated with <tt>os</tt> for use as an Ogg\r
-stream. This call is used to initialize a stream for both encode and\r
-decode. The given serial number is the serial number that will be\r
-stamped on pages of the produced bitstream (during encode), or used as\r
-a check that pages match (during decode).</p>\r
-\r
-<p>Returns zero on success, nonzero on failure.</p>\r
-\r
-<h3>\r
-int ogg_stream_packetin(ogg_stream_state *os, ogg_packet *op);\r
-</h3>\r
-\r
-<p>Used during encoding to add the given raw packet to the given Ogg\r
-bitstream. The contents of <tt>op</tt> are copied;\r
-<tt>ogg_stream_packetin</tt> does not retain any pointers into\r
-<tt>op</tt>'s storage. The encoding proccess buffers incoming packets\r
-until enough packets have been assembled to form an entire page;\r
-<tt>ogg_stream_pageout</tt> is used to read complete pages.</p>\r
-\r
-<p>Returns zero on success, nonzero on failure.</p>\r
-\r
-<h3>\r
-int ogg_stream_packetout(ogg_stream_state *os,ogg_packet *op);\r
-</h3>\r
-\r
-<p>Used during decoding to read raw packets from the given logical\r
-bitstream. <tt>ogg_stream_packetout</tt> will only return complete\r
-packets for which checksumming indicates no corruption. The size and\r
-contents of the packet exactly match those given in the encoding\r
-process. </p>\r
-\r
-<p>Returns zero if the next packet is not ready to be read (not buffered\r
-or incomplete), positive if it returned a complete packet in\r
-<tt>op</tt> and negative if there is a gap, extra bytes or corruption\r
-at this position in the bitstream (essentially that the bitstream had\r
-to be recaptured). A negative value is not necessarily an error. It\r
-would be a common occurence when seeking, for example, which requires\r
-recapture of the bitstream at the position decoding continued.</p>\r
-\r
-<p>If the return value is positive, <tt>ogg_stream_packetout</tt> placed\r
-a packet in <tt>op</tt>. The data in <tt>op</tt> points to static\r
-storage that is valid until the next call to\r
-<tt>ogg_stream_pagein</tt>, <tt>ogg_stream_clear</tt>,\r
-<tt>ogg_stream_reset</tt>, or <tt>ogg_stream_destroy</tt>. The\r
-pointers are not invalidated by more calls to\r
-<tt>ogg_stream_packetout</tt>.</p>\r
-\r
-<h3>\r
-int ogg_stream_pagein(ogg_stream_state *os, ogg_page *og);\r
-</h3>\r
-\r
-<p>Used during decoding to buffer the given complete, pre-verified page\r
-for decoding into raw Ogg packets. The given page must be framed,\r
-normally produced by <tt>ogg_sync_pageout</tt>, and from the logical\r
-bitstream associated with <tt>os</tt> (the serial numbers must match).\r
-The contents of the given page are copied; <tt>ogg_stream_pagein</tt>\r
-retains no pointers into <tt>og</tt> storage.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure.</p>\r
-\r
-<h3>\r
-int ogg_stream_pageout(ogg_stream_state *os, ogg_page *og);\r
-</h3>\r
-\r
-<p>Used during encode to read complete pages from the stream buffer. The\r
-returned page is ready for sending out to the real world.</p>\r
-\r
-<p>Returns zero if there is no complete page ready for reading. Returns\r
-nonzero when it has placed data for a complete page into\r
-<tt>og</tt>. Note that the storage returned in og points into internal\r
-storage; the pointers in <tt>og</tt> are valid until the next call to\r
-<tt>ogg_stream_pageout</tt>, <tt>ogg_stream_packetin</tt>,\r
-<tt>ogg_stream_reset</tt>, <tt>ogg_stream_clear</tt> or\r
-<tt>ogg_stream_destroy</tt>.</p>\r
-\r
-<h3>\r
-int ogg_stream_reset(ogg_stream_state *os);\r
-</h3>\r
-\r
-<p>Resets the given stream's state to that of a blank, unused stream;\r
-this may be used during encode or decode.</p>\r
-\r
-<p>Note that if used during encode, it does not alter the stream's serial\r
-number. In addition, the next page produced during encoding will be\r
-marked as the 'initial' page of the logical bitstream.</p>\r
-\r
-<p>When used during decode, this simply clears the data buffer of any\r
-pending pages. Beginning and end of stream cues are read from the\r
-bitstream and are unaffected by reset.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure. This function always\r
-succeeds.</p>\r
-\r
-<h3>\r
-char *ogg_sync_buffer(ogg_sync_state *oy, long size);\r
-</h3>\r
-\r
-<p>This call is used to buffer a raw bitstream for framing and\r
-verification. <tt>ogg_sync_buffer</tt> handles stream capture and\r
-recapture, checksumming, and division into Ogg pages (as required by\r
-<tt>ogg_stream_pagein</tt>).</p>\r
-\r
-<p><tt>ogg_sync_buffer</tt> exposes a buffer area into which the decoder\r
-copies the next (up to) <tt>size</tt> bytes. We expose the buffer\r
-(rather than taking a buffer) in order to avoid an extra copy many\r
-uses; this way, for example, <tt>read()</tt> can transfer data\r
-directly into the stream buffer without first needing to place it in\r
-temporary storage.</p>\r
-\r
-<p>Returns a pointer into <tt>oy</tt>'s internal bitstream sync buffer;\r
-the remaining space in the sync buffer is at least <tt>size</tt>\r
-bytes. The decoder need not write all of <tt>size</tt> bytes;\r
-<tt>ogg_sync_wrote</tt> is used to inform the engine how many bytes\r
-were actually written. Use of <tt>ogg_sync_wrote</tt> after writing\r
-into the exposed buffer is mandantory.</p>\r
-\r
-<h3>\r
-int ogg_sync_clear(ogg_sync_state *oy);\r
-</h3>\r
-\r
-<p><tt>ogg_sync_clear</tt>\r
-clears and deallocates the internal storage of the given Ogg sync\r
-buffer. After clearing, the sync structure is not initialized for\r
-use; <tt>ogg_sync_init</tt> must be called to reinitialize for use.\r
-Use <tt>ogg_sync_reset</tt> to reset the sync state and buffer to a\r
-fresh, intiialized state.</p>\r
-\r
-<p><tt>ogg_sync_clear</tt> does not call <tt>free()</tt> on the pointer\r
-<tt>oy</tt>, allowing use of this call on sync structures in static\r
-or automatic storage. <tt>ogg_sync_destroy</tt>is a complimentary\r
-function that frees the pointer as well.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure. This function always\r
-succeeds.</p>\r
-\r
-<h3>\r
-int ogg_sync_destroy(ogg_sync_state *oy);\r
-</h3>\r
-\r
-<p>Clears and deallocates the internal storage of the given Ogg sync\r
-buffer, then frees the storage associated with the pointer\r
-<tt>oy</tt>.</p>\r
-\r
-<p><tt>ogg_sync_clear</tt> does not call <tt>free()</tt> on the pointer\r
-<tt>oy</tt>, allowing use of that call on stream structures in static\r
-or automatic storage.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure. This function always\r
-succeeds.</p>\r
-\r
-<h3>\r
-int ogg_sync_init(ogg_sync_state *oy);\r
-</h3>\r
-\r
-<p>Initializes the sync buffer <tt>oy</tt> for use.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure. This function always\r
-succeeds.</p>\r
-\r
-<h3>\r
-int ogg_sync_pageout(ogg_sync_state *oy, ogg_page *og);\r
-</h3>\r
-\r
-<p>Reads complete, framed, verified Ogg pages from the sync buffer,\r
-placing the page data in <tt>og</tt>.</p>\r
-\r
-<p>Returns zero when there's no complete pages buffered for\r
-retrieval. Returns negative when a loss of sync or recapture occurred\r
-(this is not necessarily an error; recapture would be required after\r
-seeking, for example). Returns positive when a page is returned in\r
-<tt>og</tt>. Note that the data in <tt>og</tt> points into the sync\r
-buffer storage; the pointers are valid until the next call to\r
-<tt>ogg_sync_buffer</tt>, <tt>ogg_sync_clear</tt>,\r
-<tt>ogg_sync_destroy</tt> or <tt>ogg_sync_reset</tt>.</p>\r
-\r
-<h3>\r
-int ogg_sync_reset(ogg_sync_state *oy);\r
-</h3>\r
-\r
-<p><tt>ogg_sync_reset</tt> resets the sync state in <tt>oy</tt> to a\r
-clean, empty state. This is useful, for example, when seeking to a\r
-new location in a bitstream.</p>\r
-\r
-<p>Returns zero on success, nonzero on failure.</p>\r
-\r
-<h3>\r
-int ogg_sync_wrote(ogg_sync_state *oy, long bytes);\r
-</h3>\r
-\r
-<p>Used to inform the sync state as to how many bytes were actually\r
-written into the exposed sync buffer. It must be equal to or less\r
-than the size of the buffer requested.</p>\r
-\r
-<p>Returns zero on success and non-zero on failure; failure occurs only\r
-when the number of bytes written were larger than the buffer.</p>\r
-\r
-<div id="copyright">\r
- The Xiph Fish Logo is a\r
- trademark (™) of Xiph.Org.<br/>\r
-\r
- These pages © 1994 - 2005 Xiph.Org. All rights reserved.\r
-</div>\r
-\r
-</body>\r
-</html>\r
+<!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="https://xiph.org/"><img src="fish_xiph_org.png" alt="Fish Logo and Xiph.Org"/></a>
+</div>
+
+<h1>Programming with Xiph.Org <tt>libvorbis</tt></h1>
+
+<h2>Description</h2>
+
+<p>Libvorbis is the Xiph.Org Foundation's portable Ogg Vorbis CODEC
+implemented as a programmatic library. Libvorbis provides primitives
+to handle framing and manipulation of Ogg bitstreams (used by the
+Vorbis for streaming), a full analysis (encoding) interface as well as
+packet decoding and synthesis for playback.</p>
+
+<p>The libvorbis library does not provide any system interface; a
+full-featured demonstration player included with the library
+distribtion provides example code for a variety of system interfaces
+as well as a working example of using libvorbis in production code.</p>
+
+<h2>Encoding Overview</h2>
+
+<h2>Decoding Overview</h2>
+
+<p>Decoding a bitstream with libvorbis follows roughly the following
+steps:</p>
+
+<ol>
+<li>Frame the incoming bitstream into pages</li>
+<li>Sort the pages by logical bitstream and buffer then into logical streams</li>
+<li>Decompose the logical streams into raw packets</li>
+<li>Reconstruct segments of the original data from each packet</li>
+<li>Glue the reconstructed segments back into a decoded stream</li>
+</ol>
+
+<h3>Framing</h3>
+
+<p>An Ogg bitstream is logically arranged into pages, but to decode
+the pages, we have to find them first. The raw bitstream is first fed
+into an <tt>ogg_sync_state</tt> buffer using <tt>ogg_sync_buffer()</tt>
+and <tt>ogg_sync_wrote()</tt>. After each block we submit to the sync
+buffer, we should check to see if we can frame and extract a complete
+page or pages using <tt>ogg_sync_pageout()</tt>. Extra pages are
+buffered; allowing them to build up in the <tt>ogg_sync_state</tt>
+buffer will eventually exhaust memory.</p>
+
+<p>The Ogg pages returned from <tt>ogg_sync_pageout</tt> need not be
+decoded further to be used as landmarks in seeking; seeking can be
+either a rough process of simply jumping to approximately intuited
+portions of the bitstream, or it can be a precise bisection process
+that captures pages and inspects data position. When seeking,
+however, sequential multiplexing (chaining) must be accounted for;
+beginning play in a new logical bitstream requires initializing a
+synthesis engine with the headers from that bitstream. Vorbis
+bitstreams do not make use of concurent multiplexing (grouping).</p>
+
+<h3>Sorting</h3>
+
+<p>The pages produced by <tt>ogg_sync_pageout</tt> are then sorted by
+serial number to seperate logical bitstreams. Initialize logical
+bitstream buffers (<tt>og_stream_state</tt>) using
+<tt>ogg_stream_init()</tt>. Pages are submitted to the matching
+logical bitstream buffer using <tt>ogg_stream_pagein</tt>; the serial
+number of the page and the stream buffer must match, or the page will
+be rejected. A page submitted out of sequence will simply be noted,
+and in the course of outputting packets, the hole will be flagged
+(<tt>ogg_sync_pageout</tt> and <tt>ogg_stream_packetout</tt> will
+return a negative value at positions where they had to recapture the
+stream).</p>
+
+<h3>Extracting packets</h3>
+
+<p>After submitting page[s] to a logical stream, read available packets
+using <tt>ogg_stream_packetout</tt>.</p>
+
+<h3>Decoding packets</h3>
+
+<h3>Reassembling data segments</h3>
+
+<h2>Ogg Bitstream Manipulation Structures</h2>
+
+<p>Two of the Ogg bitstream data structures are intended to be
+transparent to the developer; the fields should be used directly.</p>
+
+<h3>ogg_packet</h3>
+
+<pre>
+typedef struct {
+ unsigned char *packet;
+ long bytes;
+ long b_o_s;
+ long e_o_s;
+
+ size64 granulepos;
+
+} ogg_packet;
+</pre>
+
+<dl>
+<dt>packet:</dt>
+<dd>a pointer to the byte data of the raw packet</dd>
+<dt>bytes:</dt>
+<dd>the size of the packet' raw data</dd>
+<dt>b_o_s:</dt>
+<dd>beginning of stream; nonzero if this is the first packet of
+ the logical bitstream</dd>
+<dt>e_o_s:</dt>
+<dd>end of stream; nonzero if this is the last packet of the
+ logical bitstream</dd>
+<dt>granulepos:</dt>
+<dd>the absolute position of this packet in the original
+ uncompressed data stream.</dd>
+</dl>
+
+<h4>encoding notes</h4>
+
+<p>The encoder is responsible for setting all of
+the fields of the packet to appropriate values before submission to
+<tt>ogg_stream_packetin()</tt>; however, it is noted that the value in
+<tt>b_o_s</tt> is ignored; the first page produced from a given
+<tt>ogg_stream_state</tt> structure will be stamped as the initial
+page. <tt>e_o_s</tt>, however, must be set; this is the means by
+which the stream encoding primitives handle end of stream and cleanup.</p>
+
+<h4>decoding notes</h4>
+
+<p><tt>ogg_stream_packetout()</tt> sets the fields
+to appropriate values. Note that granulepos will be >= 0 only in the
+case that the given packet actually represents that position (ie, only
+the last packet completed on any page will have a meaningful
+<tt>granulepos</tt>). Intervening frames will see <tt>granulepos</tt> set
+to -1.</p>
+
+<h3>ogg_page</h3>
+
+<pre>
+typedef struct {
+ unsigned char *header;
+ long header_len;
+ unsigned char *body;
+ long body_len;
+} ogg_page;
+</pre>
+
+<dl>
+<dt>header:</dt>
+<dd>pointer to the page header data</dd>
+<dt>header_len:</dt>
+<dd>length of the page header in bytes</dd>
+<dt>body:</dt>
+<dd>pointer to the page body</dd>
+<dt>body_len:</dt>
+<dd>length of the page body</dd>
+</dl>
+
+<p>Note that although the <tt>header</tt> and <tt>body</tt> pointers do
+not necessarily point into a single contiguous page vector, the page
+body must immediately follow the header in the bitstream.</p>
+
+<h2>Ogg Bitstream Manipulation Functions</h2>
+
+<h3>
+int ogg_page_bos(ogg_page *og);
+</h3>
+
+<p>Returns the 'beginning of stream' flag for the given Ogg page. The
+beginning of stream flag is set on the initial page of a logical
+bitstream.</p>
+
+<p>Zero indicates the flag is cleared (this is not the initial page of a
+logical bitstream). Nonzero indicates the flag is set (this is the
+initial page of a logical bitstream).</p>
+
+<h3>
+int ogg_page_continued(ogg_page *og);
+</h3>
+
+<p>Returns the 'packet continued' flag for the given Ogg page. The packet
+continued flag indicates whether or not the body data of this page
+begins with packet continued from a preceeding page.</p>
+
+<p>Zero (unset) indicates that the body data begins with a new packet.
+Nonzero (set) indicates that the first packet data on the page is a
+continuation from the preceeding page.</p>
+
+<h3>
+int ogg_page_eos(ogg_page *og);
+</h3>
+
+<p>Returns the 'end of stream' flag for a give Ogg page. The end of page
+flag is set on the last (terminal) page of a logical bitstream.</p>
+
+<p>Zero (unset) indicates that this is not the last page of a logical
+bitstream. Nonzero (set) indicates that this is the last page of a
+logical bitstream and that no addiitonal pages belonging to this
+bitstream may follow.</p>
+
+<h3>
+size64 ogg_page_granulepos(ogg_page *og);
+</h3>
+
+<p>Returns the position of this page as an absolute position within the
+original uncompressed data. The position, as returned, is 'frames
+encoded to date up to and including the last whole packet on this
+page'. Partial packets begun on this page but continued to the
+following page are not included. If no packet ends on this page, the
+frame position value will be equal to the frame position value of the
+preceeding page. If none of the original uncompressed data is yet
+represented in the logical bitstream (for example, the first page of a
+bitstream consists only of a header packet; this packet encodes only
+metadata), the value shall be zero.</p>
+
+<p>The units of the framenumber are determined by media mapping. A
+vorbis audio bitstream, for example, defines one frame to be the
+channel values from a single sampling period (eg, a 16 bit stereo
+bitstream consists of two samples of two bytes for a total of four
+bytes, thus a frame would be four bytes). A video stream defines one
+frame to be a single frame of video.</p>
+
+<h3>
+int ogg_page_pageno(ogg_page *og);
+</h3>
+
+<p>Returns the sequential page number of the given Ogg page. The first
+page in a logical bitstream is numbered zero; following pages are
+numbered in increasing monotonic order.</p>
+
+<h3>
+int ogg_page_serialno(ogg_page *og);
+</h3>
+
+<p>Returns the serial number of the given Ogg page. The serial number is
+used as a handle to distinguish various logical bitstreams in a
+physical Ogg bitstresm. Every logical bitstream within a
+physical bitstream must use a unique (within the scope of the physical
+bitstream) serial number, which is stamped on all bitstream pages.</p>
+
+<h3>
+int ogg_page_version(ogg_page *og);
+</h3>
+
+<p>Returns the revision of the Ogg bitstream structure of the given page.
+Currently, the only permitted number is zero. Later revisions of the
+bitstream spec will increment this version should any changes be
+incompatable.</p>
+
+<h3>
+int ogg_stream_clear(ogg_stream_state *os);
+</h3>
+
+<p>Clears and deallocates the internal storage of the given Ogg stream.
+After clearing, the stream structure is not initialized for use;
+<tt>ogg_stream_init</tt> must be called to reinitialize for use.
+Use <tt>ogg_stream_reset</tt> to reset the stream state
+to a fresh, intiialized state.</p>
+
+<p><tt>ogg_stream_clear</tt> does not call <tt>free()</tt> on the pointer
+<tt>os</tt>, allowing use of this call on stream structures in static
+or automatic storage. <tt>ogg_stream_destroy</tt>is a complimentary
+function that frees the pointer as well.</p>
+
+<p>Returns zero on success and non-zero on failure. This function always
+succeeds.</p>
+
+<h3>
+int ogg_stream_destroy(ogg_stream_state *os);
+</h3>
+
+<p>Clears and deallocates the internal storage of the given Ogg stream,
+then frees the storage associated with the pointer <tt>os</tt>.</p>
+
+<p><tt>ogg_stream_clear</tt> does not call <tt>free()</tt> on the pointer
+<tt>os</tt>, allowing use of that call on stream structures in static
+or automatic storage.</p>
+
+<p>Returns zero on success and non-zero on failure. This function always
+succeeds.</p>
+
+<h3>
+int ogg_stream_init(ogg_stream_state *os,int serialno);
+</h3>
+
+<p>Initialize the storage associated with <tt>os</tt> for use as an Ogg
+stream. This call is used to initialize a stream for both encode and
+decode. The given serial number is the serial number that will be
+stamped on pages of the produced bitstream (during encode), or used as
+a check that pages match (during decode).</p>
+
+<p>Returns zero on success, nonzero on failure.</p>
+
+<h3>
+int ogg_stream_packetin(ogg_stream_state *os, ogg_packet *op);
+</h3>
+
+<p>Used during encoding to add the given raw packet to the given Ogg
+bitstream. The contents of <tt>op</tt> are copied;
+<tt>ogg_stream_packetin</tt> does not retain any pointers into
+<tt>op</tt>'s storage. The encoding proccess buffers incoming packets
+until enough packets have been assembled to form an entire page;
+<tt>ogg_stream_pageout</tt> is used to read complete pages.</p>
+
+<p>Returns zero on success, nonzero on failure.</p>
+
+<h3>
+int ogg_stream_packetout(ogg_stream_state *os,ogg_packet *op);
+</h3>
+
+<p>Used during decoding to read raw packets from the given logical
+bitstream. <tt>ogg_stream_packetout</tt> will only return complete
+packets for which checksumming indicates no corruption. The size and
+contents of the packet exactly match those given in the encoding
+process. </p>
+
+<p>Returns zero if the next packet is not ready to be read (not buffered
+or incomplete), positive if it returned a complete packet in
+<tt>op</tt> and negative if there is a gap, extra bytes or corruption
+at this position in the bitstream (essentially that the bitstream had
+to be recaptured). A negative value is not necessarily an error. It
+would be a common occurence when seeking, for example, which requires
+recapture of the bitstream at the position decoding continued.</p>
+
+<p>If the return value is positive, <tt>ogg_stream_packetout</tt> placed
+a packet in <tt>op</tt>. The data in <tt>op</tt> points to static
+storage that is valid until the next call to
+<tt>ogg_stream_pagein</tt>, <tt>ogg_stream_clear</tt>,
+<tt>ogg_stream_reset</tt>, or <tt>ogg_stream_destroy</tt>. The
+pointers are not invalidated by more calls to
+<tt>ogg_stream_packetout</tt>.</p>
+
+<h3>
+int ogg_stream_pagein(ogg_stream_state *os, ogg_page *og);
+</h3>
+
+<p>Used during decoding to buffer the given complete, pre-verified page
+for decoding into raw Ogg packets. The given page must be framed,
+normally produced by <tt>ogg_sync_pageout</tt>, and from the logical
+bitstream associated with <tt>os</tt> (the serial numbers must match).
+The contents of the given page are copied; <tt>ogg_stream_pagein</tt>
+retains no pointers into <tt>og</tt> storage.</p>
+
+<p>Returns zero on success and non-zero on failure.</p>
+
+<h3>
+int ogg_stream_pageout(ogg_stream_state *os, ogg_page *og);
+</h3>
+
+<p>Used during encode to read complete pages from the stream buffer. The
+returned page is ready for sending out to the real world.</p>
+
+<p>Returns zero if there is no complete page ready for reading. Returns
+nonzero when it has placed data for a complete page into
+<tt>og</tt>. Note that the storage returned in og points into internal
+storage; the pointers in <tt>og</tt> are valid until the next call to
+<tt>ogg_stream_pageout</tt>, <tt>ogg_stream_packetin</tt>,
+<tt>ogg_stream_reset</tt>, <tt>ogg_stream_clear</tt> or
+<tt>ogg_stream_destroy</tt>.</p>
+
+<h3>
+int ogg_stream_reset(ogg_stream_state *os);
+</h3>
+
+<p>Resets the given stream's state to that of a blank, unused stream;
+this may be used during encode or decode.</p>
+
+<p>Note that if used during encode, it does not alter the stream's serial
+number. In addition, the next page produced during encoding will be
+marked as the 'initial' page of the logical bitstream.</p>
+
+<p>When used during decode, this simply clears the data buffer of any
+pending pages. Beginning and end of stream cues are read from the
+bitstream and are unaffected by reset.</p>
+
+<p>Returns zero on success and non-zero on failure. This function always
+succeeds.</p>
+
+<h3>
+char *ogg_sync_buffer(ogg_sync_state *oy, long size);
+</h3>
+
+<p>This call is used to buffer a raw bitstream for framing and
+verification. <tt>ogg_sync_buffer</tt> handles stream capture and
+recapture, checksumming, and division into Ogg pages (as required by
+<tt>ogg_stream_pagein</tt>).</p>
+
+<p><tt>ogg_sync_buffer</tt> exposes a buffer area into which the decoder
+copies the next (up to) <tt>size</tt> bytes. We expose the buffer
+(rather than taking a buffer) in order to avoid an extra copy many
+uses; this way, for example, <tt>read()</tt> can transfer data
+directly into the stream buffer without first needing to place it in
+temporary storage.</p>
+
+<p>Returns a pointer into <tt>oy</tt>'s internal bitstream sync buffer;
+the remaining space in the sync buffer is at least <tt>size</tt>
+bytes. The decoder need not write all of <tt>size</tt> bytes;
+<tt>ogg_sync_wrote</tt> is used to inform the engine how many bytes
+were actually written. Use of <tt>ogg_sync_wrote</tt> after writing
+into the exposed buffer is mandantory.</p>
+
+<h3>
+int ogg_sync_clear(ogg_sync_state *oy);
+</h3>
+
+<p><tt>ogg_sync_clear</tt>
+clears and deallocates the internal storage of the given Ogg sync
+buffer. After clearing, the sync structure is not initialized for
+use; <tt>ogg_sync_init</tt> must be called to reinitialize for use.
+Use <tt>ogg_sync_reset</tt> to reset the sync state and buffer to a
+fresh, intiialized state.</p>
+
+<p><tt>ogg_sync_clear</tt> does not call <tt>free()</tt> on the pointer
+<tt>oy</tt>, allowing use of this call on sync structures in static
+or automatic storage. <tt>ogg_sync_destroy</tt>is a complimentary
+function that frees the pointer as well.</p>
+
+<p>Returns zero on success and non-zero on failure. This function always
+succeeds.</p>
+
+<h3>
+int ogg_sync_destroy(ogg_sync_state *oy);
+</h3>
+
+<p>Clears and deallocates the internal storage of the given Ogg sync
+buffer, then frees the storage associated with the pointer
+<tt>oy</tt>.</p>
+
+<p>An alternative function,<tt>ogg_sync_clear</tt>, does not call
+<tt>free()</tt> on the pointer <tt>oy</tt>, allowing use of that call on
+stream structures in static or automatic storage.</p>
+
+<p>Returns zero on success and non-zero on failure. This function always
+succeeds.</p>
+
+<h3>
+int ogg_sync_init(ogg_sync_state *oy);
+</h3>
+
+<p>Initializes the sync buffer <tt>oy</tt> for use.</p>
+
+<p>Returns zero on success and non-zero on failure. This function always
+succeeds.</p>
+
+<h3>
+int ogg_sync_pageout(ogg_sync_state *oy, ogg_page *og);
+</h3>
+
+<p>Reads complete, framed, verified Ogg pages from the sync buffer,
+placing the page data in <tt>og</tt>.</p>
+
+<p>Returns zero when there's no complete pages buffered for
+retrieval. Returns negative when a loss of sync or recapture occurred
+(this is not necessarily an error; recapture would be required after
+seeking, for example). Returns positive when a page is returned in
+<tt>og</tt>. Note that the data in <tt>og</tt> points into the sync
+buffer storage; the pointers are valid until the next call to
+<tt>ogg_sync_buffer</tt>, <tt>ogg_sync_clear</tt>,
+<tt>ogg_sync_destroy</tt> or <tt>ogg_sync_reset</tt>.</p>
+
+<h3>
+int ogg_sync_reset(ogg_sync_state *oy);
+</h3>
+
+<p><tt>ogg_sync_reset</tt> resets the sync state in <tt>oy</tt> to a
+clean, empty state. This is useful, for example, when seeking to a
+new location in a bitstream.</p>
+
+<p>Returns zero on success, nonzero on failure.</p>
+
+<h3>
+int ogg_sync_wrote(ogg_sync_state *oy, long bytes);
+</h3>
+
+<p>Used to inform the sync state as to how many bytes were actually
+written into the exposed sync buffer. It must be equal to or less
+than the size of the buffer requested.</p>
+
+<p>Returns zero on success and non-zero on failure; failure occurs only
+when the number of bytes written were larger than the buffer.</p>
+
+<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>
projects / platform / upstream / libvorbis.git / blobdiff