1159b3361Sopenharmony_ci<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 2159b3361Sopenharmony_ci "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 3159b3361Sopenharmony_ci<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> 4159b3361Sopenharmony_ci <head> 5159b3361Sopenharmony_ci <meta name="generator" content="PSPad editor, www.pspad.com" /> 6159b3361Sopenharmony_ci <meta http-equiv="content-type" content="text/html; charset=UTF-8" /> 7159b3361Sopenharmony_ci <link rel="stylesheet" type="text/css" href="styles/lame.css" /> 8159b3361Sopenharmony_ci <title>LAME MP3 Encoder ::Average Bit Rate (ABR)</title> 9159b3361Sopenharmony_ci </head> 10159b3361Sopenharmony_ci <body> 11159b3361Sopenharmony_ci<div id="menu"> 12159b3361Sopenharmony_ci <ul> 13159b3361Sopenharmony_ci <li><a href="index.html">Index page</a></li> 14159b3361Sopenharmony_ci <li><a href="about.html">About LAME</a></li> 15159b3361Sopenharmony_ci <li><a style="border: 0" href="introduction.html">Intro to encoding</a> 16159b3361Sopenharmony_ci <div id="submenu"> 17159b3361Sopenharmony_ci <ul> 18159b3361Sopenharmony_ci <li><a href="cbr.html">CBR </a></li> 19159b3361Sopenharmony_ci <li><a href="abr.html">ABR </a></li> 20159b3361Sopenharmony_ci <li><a href="vbr.html">VBR </a></li> 21159b3361Sopenharmony_ci <li><a style="border: 0" href="ms_stereo.html">M/S Stereo</a></li> 22159b3361Sopenharmony_ci </ul> 23159b3361Sopenharmony_ci </div> 24159b3361Sopenharmony_ci </li> 25159b3361Sopenharmony_ci <li><a href="usage.html">Usage of LAME</a></li> 26159b3361Sopenharmony_ci <li><a href="history.html">Version history</a></li> 27159b3361Sopenharmony_ci <li><a href="contributors.html">Coders of LAME</a></li> 28159b3361Sopenharmony_ci <li><a href="contact.html">Contact LAME</a></li> 29159b3361Sopenharmony_ci <li><a style="border: 0" href="links.html">LAME links</a></li> 30159b3361Sopenharmony_ci </ul> 31159b3361Sopenharmony_ci</div> 32159b3361Sopenharmony_ci<div id="container"> 33159b3361Sopenharmony_ci<div id="content"> 34159b3361Sopenharmony_ci <div align="center"> 35159b3361Sopenharmony_ci <img src="images/logo.gif" width="358" height="231" alt="LAME Official Logo" /> 36159b3361Sopenharmony_ci <h2 class="hilight">LAME - Average Bit Rate (ABR)</h2> 37159b3361Sopenharmony_ci </div> 38159b3361Sopenharmony_ci <p>Suggested usage:</p> 39159b3361Sopenharmony_ci <blockquote class="code">lame --abr 128 input.wav output.mp3</blockquote> 40159b3361Sopenharmony_ci <p> 41159b3361Sopenharmony_ci ABR is a mix between CBR and VBR. 42159b3361Sopenharmony_ci </p> 43159b3361Sopenharmony_ci <p> 44159b3361Sopenharmony_ci Like CBR, the files will have the (approximate) bitrate specified in the 45159b3361Sopenharmony_ci commandline, and uses the CBR algorithm to compute the number of bits needed 46159b3361Sopenharmony_ci to encode each frame.<br/> 47159b3361Sopenharmony_ci </p> 48159b3361Sopenharmony_ci <p> 49159b3361Sopenharmony_ci Like VBR, the files will use different frame bitrates so instead of relying on 50159b3361Sopenharmony_ci bit reservoir like CBR, each frame just uses the smallest possible bitrate 51159b3361Sopenharmony_ci that can encode it. 52159b3361Sopenharmony_ci </p> 53159b3361Sopenharmony_ci <p> 54159b3361Sopenharmony_ci The difference between ABR and true VBR is in how the desired number of bits 55159b3361Sopenharmony_ci is chosen. The true VBR mode determines the number of bits based on the 56159b3361Sopenharmony_ci quantization noise. VBR figures out how many bits are needed so that the 57159b3361Sopenharmony_ci quantization noise is less than the allowed masking. 58159b3361Sopenharmony_ci </p> 59159b3361Sopenharmony_ci <p> 60159b3361Sopenharmony_ci ABR mode uses the CBR formula to determine the desired number of bits. This 61159b3361Sopenharmony_ci formula is based on the perceptual entropy, which is a rough measure of how 62159b3361Sopenharmony_ci difficult the frame is to encode. 63159b3361Sopenharmony_ci </p> 64159b3361Sopenharmony_ci <p> 65159b3361Sopenharmony_ci The majority of frames in a VBR MP3 produced with an ABR method is normally at 66159b3361Sopenharmony_ci or near the target bitrate chosen by the user, but each frame can still 67159b3361Sopenharmony_ci potentially vary within the normal range of 8 to 320 kbps. The ABR encoder will 68159b3361Sopenharmony_ci typically limit the range of bitrates it can choose from, or will greatly favor 69159b3361Sopenharmony_ci certain bitrates, in an effort to ensure that the average comes out near the 70159b3361Sopenharmony_ci target. 71159b3361Sopenharmony_ci </p> 72159b3361Sopenharmony_ci <h3>Who should use ABR</h3> 73159b3361Sopenharmony_ci <p> 74159b3361Sopenharmony_ci ABR encoding is desirable for users who want the general benefits of VBR (an 75159b3361Sopenharmony_ci optimum bitrate from frame to frame) but with a relatively predictable file size 76159b3361Sopenharmony_ci like they would get with constant bitrate (CBR), and a greater preference for 77159b3361Sopenharmony_ci bitrates that are near a desired target. Inevitably, some frames will be encoded 78159b3361Sopenharmony_ci with more bits than necessary, but the result will always be equal to or better 79159b3361Sopenharmony_ci than that of CBR for the target bitrate. 80159b3361Sopenharmony_ci </p> 81159b3361Sopenharmony_ci</div> 82159b3361Sopenharmony_ci<div id="footer"> 83159b3361Sopenharmony_ci 84159b3361Sopenharmony_ci<a href="http://sourceforge.net/projects/lame"><img src="images/sflogo.gif" 85159b3361Sopenharmony_ci alt="Get LAME (Lame Aint an MP3 Encoder) at SourceForge.net. Fast, secure and Free Open Source software downloads" 86159b3361Sopenharmony_ci border="0" height="30" width="120" /></a> 87159b3361Sopenharmony_ci 88159b3361Sopenharmony_ci<a href="http://validator.w3.org/#validate_by_upload"><img src="images/valid-xhtml10.png" 89159b3361Sopenharmony_ci alt="Valid XHTML 1.0 Transitional" border="0" height="31" width="88" /></a> 90159b3361Sopenharmony_ci 91159b3361Sopenharmony_ci<a href="http://jigsaw.w3.org/css-validator/"><img src="images/valid-css.png" 92159b3361Sopenharmony_ci alt="Valid CSS!" border="0" height="31" width="88" /></a> 93159b3361Sopenharmony_ci 94159b3361Sopenharmony_ci<p>HTML markup and design by <a 95159b3361Sopenharmony_cihref="http://www.rarewares.org" target="_blank">Roberto Amorim</a> and <a 96159b3361Sopenharmony_cihref="http://www.maresweb.de" target="_blank">Sebastian Mares</a>. Logo by <a 97159b3361Sopenharmony_cihref="http://www.brightercreative.co.uk">Sam Fisher</a>.</p> 98159b3361Sopenharmony_ci 99159b3361Sopenharmony_ci</div> 100159b3361Sopenharmony_ci</div> 101159b3361Sopenharmony_ci 102159b3361Sopenharmony_ci</body> 103159b3361Sopenharmony_ci</html> 104
