summaryrefslogtreecommitdiffhomepage
path: root/vorbis/doc/vorbisfile/crosslap.html
diff options
context:
space:
mode:
Diffstat (limited to 'vorbis/doc/vorbisfile/crosslap.html')
-rw-r--r--vorbis/doc/vorbisfile/crosslap.html121
1 files changed, 0 insertions, 121 deletions
diff --git a/vorbis/doc/vorbisfile/crosslap.html b/vorbis/doc/vorbisfile/crosslap.html
deleted file mode 100644
index 9d28b0b..0000000
--- a/vorbis/doc/vorbisfile/crosslap.html
+++ /dev/null
@@ -1,121 +0,0 @@
-<html>
-
-<head>
-<title>Vorbisfile - Sample Crosslapping</title>
-<link rel=stylesheet href="style.css" type="text/css">
-</head>
-
-<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
-<table border=0 width=100%>
-<tr>
-<td><p class=tiny>Vorbisfile documentation</p></td>
-<td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
-</tr>
-</table>
-
-<h1>What is Crosslapping?</h1>
-
-<p>Crosslapping blends two samples together using a window function,
-such that any sudden discontinuities between the samples that may
-cause clicks or thumps are eliminated or blended away. The technique
-is nearly identical to how Vorbis internally splices together frames
-of audio data during normal decode. API functions are provided to <a
-href="ov_crosslap.html">crosslap transitions between seperate
-streams</a>, or to crosslap when <a href="seeking.html">seeking within
-a single stream</a>.
-
-<h1>Why Crosslap?</h1>
-<h2>The source of boundary clicks</h2>
-
-<p>Vorbis is a lossy compression format such that any compressed
-signal is at best a close approximation of the original. The
-approximation may be very good (ie, indistingushable to the human
-ear), but it is an approximation nonetheless. Even if a sample or set
-of samples is contructed carefully such that transitions from one to
-another match perfectly in the original, the compression process
-introduces minute amplitude and phase errors. It's an unavoidable
-result of such high compression rates.
-
-<p>If an application transitions instantly from one sample to another,
-any tiny discrepancy introduced in the lossy compression process
-becomes audible as a stairstep discontinuity. Even if the discrepancy
-in a normal lapped frame is only .1dB (usually far below the
-threshhold of perception), that's a sudden cliff of 380 steps in a 16
-bit sample (when there's a boundary with no lapping).
-
-<h2>I thought Vorbis was gapless</h2>
-
-<p>It is. Vorbis introduces no extra samples at the beginning or end
-of a stream, nor does it remove any samples. Gapless encoding
-eliminates 99% of the click, pop or outright blown speaker that would
-occur if boundaries had gaps or made no effort to align
-transitions. However, gapless encoding is not enough to entirely
-eliminate stairstep discontinuities all the time for exactly the
-reasons described above.
-
-<p>Frame lapping, like Vorbis performs internally during continuous
-playback, is necessary to eliminate that last epsilon of trouble.
-
-<h1>Easiest Crosslap</h1>
-
-The easiest way to perform crosslapping in Vorbis is to use the
-lapping functions with no other extra effort. These functions behave
-identically to when lapping isn't used except to provide
-at-least-very-good lapping results. Crosslapping will not introduce
-any samples into or remove any samples from the decoded audio; the
-only difference is that the transition is lapped. Lapping occurs from
-the current PCM position (either in the old stream, or at the position
-prior to calling a lapping seek) forward into the next
-half-short-block of audio data to be read from the new stream or
-position.
-
-<p>Ideally, vorbisfile internally reads an extra frame of audio from
-the old stream/position to perform lapping into the new
-stream/position. However, automagic crosslapping works properly even
-if the old stream/position is at EOF. In this case, the synthetic
-post-extrapolation generated by the encoder to pad out the last block
-with appropriate data (and avoid encoding a stairstep, which is
-inefficient) is used for crosslapping purposes. Although this is
-synthetic data, the result is still usually completely unnoticable
-even in careful listening (and always preferable to a click or pop).
-
-<p>Vorbisfile will lap between streams of differing numbers of
-channels. Any extra channels from the old stream are ignored; playback
-of these channels simply ends. Extra channels in the new stream are
-lapped from silence. Vorbisfile will also lap between streams links
-of differing sample rates. In this case, the sample rates are ignored
-(no implicit resampling is done to match playback). It is up to the
-application developer to decide if this behavior makes any sense in a
-given context; in practical use, these default behaviors perform
-sensibly.
-
-<h1>Best Crosslap</h1>
-
-<p>To acheive the best possible crosslapping results, avoid the case
-where synthetic extrapolation data is used for crosslapping. That is,
-design loops and samples such that a little bit of data is left over
-in sample A when seeking to sample B. Normally, the end of sample A
-and the beginning of B would overlap exactly; this allows
-crosslapping to perform exactly as it would within vorbis when
-stitching audio frames together into continuous decoded audio.
-
-<p>The optimal amount of overlap is half a short-block, and this
-varies by compression mode. Each encoder will vary in exact block
-size selection; for vorbis 1.0, for -q0 through -q10 and 44kHz or
-greater, a half-short block is 64 samples.
-
-<br><br>
-<hr noshade>
-<table border=0 width=100%>
-<tr valign=top>
-<td><p class=tiny>copyright &copy; 2000-2010 Xiph.Org</p></td>
-<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
-</tr><tr>
-<td><p class=tiny>Vorbisfile documentation</p></td>
-<td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
-</tr>
-</table>
-
-</body>
-
-</html>