112 lines
4.1 KiB
HTML
112 lines
4.1 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 ::Average Bit Rate (ABR)</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 - Average Bit Rate (ABR)</h2>
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</div>
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<p>Suggested usage:</p>
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<blockquote class="code">lame --abr 128 input.wav output.mp3</blockquote>
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<p>
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ABR is a mix between CBR and VBR.
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</p>
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<p>
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Like CBR, the files will have the (approximate) bitrate specified in the
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commandline, and uses the CBR algorithm to compute the number of bits needed
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to encode each frame.<br/>
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</p>
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<p>
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Like VBR, the files will use different frame bitrates so instead of relying on
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bit reservoir like CBR, each frame just uses the smallest possible bitrate
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that can encode it.
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</p>
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<p>
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The difference between ABR and true VBR is in how the desired number of bits
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is chosen. The true VBR mode determines the number of bits based on the
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quantization noise. VBR figures out how many bits are needed so that the
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quantization noise is less than the allowed masking.
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</p>
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<p>
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ABR mode uses the CBR formula to determine the desired number of bits. This
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formula is based on the perceptual entropy, which is a rough measure of how
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difficult the frame is to encode.
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</p>
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<p>
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The majority of frames in a VBR MP3 produced with an ABR method is normally at
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or near the target bitrate chosen by the user, but each frame can still
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potentially vary within the normal range of 8 to 320 kbps. The ABR encoder will
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typically limit the range of bitrates it can choose from, or will greatly favor
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certain bitrates, in an effort to ensure that the average comes out near the
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target.
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</p>
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<h3>Who should use ABR</h3>
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<p>
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ABR encoding is desirable for users who want the general benefits of VBR (an
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optimum bitrate from frame to frame) but with a relatively predictable file size
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like they would get with constant bitrate (CBR), and a greater preference for
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bitrates that are near a desired target. Inevitably, some frames will be encoded
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with more bits than necessary, but the result will always be equal to or better
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than that of CBR for the target bitrate.
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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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<a href="http://validator.w3.org/#validate_by_upload"><img src="images/valid-xhtml10.png"
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alt="Valid XHTML 1.0 Transitional" border="0" height="31" width="88" /></a>
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<a href="http://jigsaw.w3.org/css-validator/"><img src="images/valid-css.png"
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alt="Valid CSS!" border="0" height="31" width="88" /></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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</div>
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</body>
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</html> |