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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>
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-<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-15"/>
-<title>Ogg Vorbis Documentation</title>
-
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-body {
- margin: 0 18px 0 18px;
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- font-weight: bold;
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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>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 (&trade;) of Xiph.Org.<br/>
-
- These pages &copy; 1994 - 2005 Xiph.Org. All rights reserved.
-</div>
-
-</body>
-</html>