1<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 2 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4 <head> 5 <meta name="generator" content="PSPad editor, www.pspad.com" /> 6 <meta http-equiv="content-type" content="text/html; charset=UTF-8" /> 7 <link rel="stylesheet" type="text/css" href="styles/lame.css" /> 8 <title>LAME MP3 Encoder ::Average Bit Rate (ABR)</title> 9 </head> 10 <body> 11<div id="menu"> 12 <ul> 13 <li><a href="index.html">Index page</a></li> 14 <li><a href="about.html">About LAME</a></li> 15 <li><a style="border: 0" href="introduction.html">Intro to encoding</a> 16 <div id="submenu"> 17 <ul> 18 <li><a href="cbr.html">CBR </a></li> 19 <li><a href="abr.html">ABR </a></li> 20 <li><a href="vbr.html">VBR </a></li> 21 <li><a style="border: 0" href="ms_stereo.html">M/S Stereo</a></li> 22 </ul> 23 </div> 24 </li> 25 <li><a href="usage.html">Usage of LAME</a></li> 26 <li><a href="history.html">Version history</a></li> 27 <li><a href="contributors.html">Coders of LAME</a></li> 28 <li><a href="contact.html">Contact LAME</a></li> 29 <li><a style="border: 0" href="links.html">LAME links</a></li> 30 </ul> 31</div> 32<div id="container"> 33<div id="content"> 34 <div align="center"> 35 <img src="images/logo.gif" width="358" height="231" alt="LAME Official Logo" /> 36 <h2 class="hilight">LAME - Average Bit Rate (ABR)</h2> 37 </div> 38 <p>Suggested usage:</p> 39 <blockquote class="code">lame --abr 128 input.wav output.mp3</blockquote> 40 <p> 41 ABR is a mix between CBR and VBR. 42 </p> 43 <p> 44 Like CBR, the files will have the (approximate) bitrate specified in the 45 commandline, and uses the CBR algorithm to compute the number of bits needed 46 to encode each frame.<br/> 47 </p> 48 <p> 49 Like VBR, the files will use different frame bitrates so instead of relying on 50 bit reservoir like CBR, each frame just uses the smallest possible bitrate 51 that can encode it. 52 </p> 53 <p> 54 The difference between ABR and true VBR is in how the desired number of bits 55 is chosen. The true VBR mode determines the number of bits based on the 56 quantization noise. VBR figures out how many bits are needed so that the 57 quantization noise is less than the allowed masking. 58 </p> 59 <p> 60 ABR mode uses the CBR formula to determine the desired number of bits. This 61 formula is based on the perceptual entropy, which is a rough measure of how 62 difficult the frame is to encode. 63 </p> 64 <p> 65 The majority of frames in a VBR MP3 produced with an ABR method is normally at 66 or near the target bitrate chosen by the user, but each frame can still 67 potentially vary within the normal range of 8 to 320 kbps. The ABR encoder will 68 typically limit the range of bitrates it can choose from, or will greatly favor 69 certain bitrates, in an effort to ensure that the average comes out near the 70 target. 71 </p> 72 <h3>Who should use ABR</h3> 73 <p> 74 ABR encoding is desirable for users who want the general benefits of VBR (an 75 optimum bitrate from frame to frame) but with a relatively predictable file size 76 like they would get with constant bitrate (CBR), and a greater preference for 77 bitrates that are near a desired target. Inevitably, some frames will be encoded 78 with more bits than necessary, but the result will always be equal to or better 79 than that of CBR for the target bitrate. 80 </p> 81</div> 82<div id="footer"> 83 84<a href="http://sourceforge.net/projects/lame"><img src="images/sflogo.gif" 85 alt="Get LAME (Lame Aint an MP3 Encoder) at SourceForge.net. Fast, secure and Free Open Source software downloads" 86 border="0" height="30" width="120" /></a> 87 88<a href="http://validator.w3.org/#validate_by_upload"><img src="images/valid-xhtml10.png" 89 alt="Valid XHTML 1.0 Transitional" border="0" height="31" width="88" /></a> 90 91<a href="http://jigsaw.w3.org/css-validator/"><img src="images/valid-css.png" 92 alt="Valid CSS!" border="0" height="31" width="88" /></a> 93 94<p>HTML markup and design by <a 95href="http://www.rarewares.org" target="_blank">Roberto Amorim</a> and <a 96href="http://www.maresweb.de" target="_blank">Sebastian Mares</a>. Logo by <a 97href="http://www.brightercreative.co.uk">Sam Fisher</a>.</p> 98 99</div> 100</div> 101 102</body> 103</html> 104
