104 lines
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4.4 KiB
HTML
104 lines
No EOL
4.4 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
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<head>
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<meta name="generator" content="PSPad editor, www.pspad.com" />
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<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
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<link rel="stylesheet" type="text/css" href="styles/lame.css" />
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<title>LAME MP3 Encoder :: Constant Bit Rate</title>
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</head>
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<body>
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<div id="menu">
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<ul>
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<li><a href="index.html">Index page</a></li>
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<li><a href="about.html">About LAME</a></li>
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<li><a style="border: 0" href="introduction.html">Intro to encoding</a>
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<div id="submenu">
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<ul>
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<li><a href="cbr.html">CBR </a></li>
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<li><a href="abr.html">ABR </a></li>
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<li><a href="vbr.html">VBR </a></li>
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<li><a style="border: 0" href="ms_stereo.html">M/S Stereo</a></li>
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</ul>
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</div>
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</li>
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<li><a href="usage.html">Usage of LAME</a></li>
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<li><a href="history.html">Version history</a></li>
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<li><a href="contributors.html">Coders of LAME</a></li>
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<li><a href="contact.html">Contact LAME</a></li>
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<li><a style="border: 0" href="links.html">LAME links</a></li>
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</ul>
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</div>
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<div id="container">
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<div id="content">
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<div align="center">
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<img src="images/logo.gif" width="358" height="231" alt="LAME Official Logo" />
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<h2 class="hilight">LAME - Constant Bit Rate</h2>
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</div>
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<p>Suggested usage:</p>
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<blockquote class="code">lame -b 128 input.wav output.mp3</blockquote>
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<p>
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CBR encoding is the basic encoding mode of MP3: The bitrate is kept constant
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across the entire file, which means the same number of bits is allocated to
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encode each second of audio, and internally, frames of audio data occur at
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regular, predictable intervals, given a predictable file size for a given
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duration. CBR is therefore the "opposite" of <a href="vbr.html">VBR</a>.
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</p>
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<p>
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That said, in some formats there may be some variability in the number of bits
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that contain actual audio information from frame to frame. This concept manifests
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in the <i>bit reservoir</i> of MP3s. In a CBR MP3, even though the frames are of
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a fixed size, the audio data is not necessarily distributed consistently between
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them; audio for one frame might use fewer bits than the frame has, so that frame
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adds the spare bits to a <i>reservoir</i> that can supplement the bits allocated
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to the next frame. Thus, the effective bitrate is allowed to vary somewhat in a
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CBR MP3, even though there is a fixed number of frames for the duration of audio.
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For example, for a 256kbps file, the bitrate of a single frame can be up to 320
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kbps, but the frame immediately before and/or after that one would have to use
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fewer bits, whereas in VBR, there would be no such restriction. Consequently, the
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amount of variability across the entire MP3 is not as great as that afforded by
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VBR, but it is not insignificant; a CBR encoder that does not efficiently use
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the reservoir will likely produce a lower quality file than one that does.
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</p>
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<p>
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<a href="abr.html">ABR</a> is a more flexible way to encode where filesize is
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important, but still giving some flexibility to choose frame sizes.
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</p>
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<h3>Who should use CBR</h3>
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<p>
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CBR is useful for people who are concerned about maintaining maximum
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compatibility, especially with certain streaming applications and some
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hardware-based decoders that don't reliably support VBR.
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</p>
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<p>
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CBR is also useful for people who desire the ability to obtain accurate
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estimates of the bitrate or approximate duration of a file's decoded audio
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without scanning and partially decoding the entire file.
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</p>
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</div>
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<div id="footer">
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<a href="http://sourceforge.net/projects/lame"><img src="http://sflogo.sourceforge.net/sflogo.php?group_id=290&type=12"
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alt="Get LAME (Lame Aint an MP3 Encoder) at SourceForge.net. Fast, secure and Free Open Source software downloads"
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border="0" height="30" width="120" /></a>
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<p>HTML markup and design by <a
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href="http://www.rjamorim.com" target="_blank">Roberto Amorim</a> and <a
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href="http://www.maresweb.de" target="_blank">Sebastian Mares</a>. Logo by <a
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href="http://www.brightercreative.co.uk">Sam Fisher</a>.</p>
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</div>
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</body>
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</html> |