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 :: Constant Bit Rate</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 - Constant Bit Rate</h2> 37159b3361Sopenharmony_ci </div> 38159b3361Sopenharmony_ci <p>Suggested usage:</p> 39159b3361Sopenharmony_ci <blockquote class="code">lame -b 128 input.wav output.mp3</blockquote> 40159b3361Sopenharmony_ci <p> 41159b3361Sopenharmony_ci CBR encoding is the basic encoding mode of MP3: The bitrate is kept constant 42159b3361Sopenharmony_ci across the entire file, which means the same number of bits is allocated to 43159b3361Sopenharmony_ci encode each second of audio, and internally, frames of audio data occur at 44159b3361Sopenharmony_ci regular, predictable intervals, given a predictable file size for a given 45159b3361Sopenharmony_ci duration. CBR is therefore the "opposite" of <a href="vbr.html">VBR</a>. 46159b3361Sopenharmony_ci </p> 47159b3361Sopenharmony_ci <p> 48159b3361Sopenharmony_ci That said, in some formats there may be some variability in the number of bits 49159b3361Sopenharmony_ci that contain actual audio information from frame to frame. This concept manifests 50159b3361Sopenharmony_ci in the <i>bit reservoir</i> of MP3s. In a CBR MP3, even though the frames are of 51159b3361Sopenharmony_ci a fixed size, the audio data is not necessarily distributed consistently between 52159b3361Sopenharmony_ci them; audio for one frame might use fewer bits than the frame has, so that frame 53159b3361Sopenharmony_ci adds the spare bits to a <i>reservoir</i> that can supplement the bits allocated 54159b3361Sopenharmony_ci to the next frame. Thus, the effective bitrate is allowed to vary somewhat in a 55159b3361Sopenharmony_ci CBR MP3, even though there is a fixed number of frames for the duration of audio. 56159b3361Sopenharmony_ci For example, for a 256kbps file, the bitrate of a single frame can be up to 320 57159b3361Sopenharmony_ci kbps, but the frame immediately before and/or after that one would have to use 58159b3361Sopenharmony_ci fewer bits, whereas in VBR, there would be no such restriction. Consequently, the 59159b3361Sopenharmony_ci amount of variability across the entire MP3 is not as great as that afforded by 60159b3361Sopenharmony_ci VBR, but it is not insignificant; a CBR encoder that does not efficiently use 61159b3361Sopenharmony_ci the reservoir will likely produce a lower quality file than one that does. 62159b3361Sopenharmony_ci </p> 63159b3361Sopenharmony_ci <p> 64159b3361Sopenharmony_ci <a href="abr.html">ABR</a> is a more flexible way to encode where filesize is 65159b3361Sopenharmony_ci important, but still giving some flexibility to choose frame sizes. 66159b3361Sopenharmony_ci </p> 67159b3361Sopenharmony_ci <h3>Who should use CBR</h3> 68159b3361Sopenharmony_ci <p> 69159b3361Sopenharmony_ci CBR is useful for people who are concerned about maintaining maximum 70159b3361Sopenharmony_ci compatibility, especially with certain streaming applications and some 71159b3361Sopenharmony_ci hardware-based decoders that don't reliably support VBR. 72159b3361Sopenharmony_ci </p> 73159b3361Sopenharmony_ci <p> 74159b3361Sopenharmony_ci CBR is also useful for people who desire the ability to obtain accurate 75159b3361Sopenharmony_ci estimates of the bitrate or approximate duration of a file's decoded audio 76159b3361Sopenharmony_ci without scanning and partially decoding the entire file. 77159b3361Sopenharmony_ci </p> 78159b3361Sopenharmony_ci</div> 79159b3361Sopenharmony_ci<div id="footer"> 80159b3361Sopenharmony_ci 81159b3361Sopenharmony_ci<a href="http://sourceforge.net/projects/lame"><img src="images/sflogo.gif" 82159b3361Sopenharmony_ci alt="Get LAME (Lame Aint an MP3 Encoder) at SourceForge.net. 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