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 :: Constant Bit Rate</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 - Constant Bit Rate</h2> 37 </div> 38 <p>Suggested usage:</p> 39 <blockquote class="code">lame -b 128 input.wav output.mp3</blockquote> 40 <p> 41 CBR encoding is the basic encoding mode of MP3: The bitrate is kept constant 42 across the entire file, which means the same number of bits is allocated to 43 encode each second of audio, and internally, frames of audio data occur at 44 regular, predictable intervals, given a predictable file size for a given 45 duration. CBR is therefore the "opposite" of <a href="vbr.html">VBR</a>. 46 </p> 47 <p> 48 That said, in some formats there may be some variability in the number of bits 49 that contain actual audio information from frame to frame. This concept manifests 50 in the <i>bit reservoir</i> of MP3s. In a CBR MP3, even though the frames are of 51 a fixed size, the audio data is not necessarily distributed consistently between 52 them; audio for one frame might use fewer bits than the frame has, so that frame 53 adds the spare bits to a <i>reservoir</i> that can supplement the bits allocated 54 to the next frame. Thus, the effective bitrate is allowed to vary somewhat in a 55 CBR MP3, even though there is a fixed number of frames for the duration of audio. 56 For example, for a 256kbps file, the bitrate of a single frame can be up to 320 57 kbps, but the frame immediately before and/or after that one would have to use 58 fewer bits, whereas in VBR, there would be no such restriction. Consequently, the 59 amount of variability across the entire MP3 is not as great as that afforded by 60 VBR, but it is not insignificant; a CBR encoder that does not efficiently use 61 the reservoir will likely produce a lower quality file than one that does. 62 </p> 63 <p> 64 <a href="abr.html">ABR</a> is a more flexible way to encode where filesize is 65 important, but still giving some flexibility to choose frame sizes. 66 </p> 67 <h3>Who should use CBR</h3> 68 <p> 69 CBR is useful for people who are concerned about maintaining maximum 70 compatibility, especially with certain streaming applications and some 71 hardware-based decoders that don't reliably support VBR. 72 </p> 73 <p> 74 CBR is also useful for people who desire the ability to obtain accurate 75 estimates of the bitrate or approximate duration of a file's decoded audio 76 without scanning and partially decoding the entire file. 77 </p> 78</div> 79<div id="footer"> 80 81<a href="http://sourceforge.net/projects/lame"><img src="images/sflogo.gif" 82 alt="Get LAME (Lame Aint an MP3 Encoder) at SourceForge.net. Fast, secure and Free Open Source software downloads" 83 border="0" height="30" width="120" /></a> 84 85<a href="http://validator.w3.org/#validate_by_upload"><img src="images/valid-xhtml10.png" 86 alt="Valid XHTML 1.0 Transitional" border="0" height="31" width="88" /></a> 87 88<a href="http://jigsaw.w3.org/css-validator/"><img src="images/valid-css.png" 89 alt="Valid CSS!" border="0" height="31" width="88" /></a> 90 91<p>HTML markup and design by <a 92href="http://www.rarewares.org" target="_blank">Roberto Amorim</a> and <a 93href="http://www.maresweb.de" target="_blank">Sebastian Mares</a>. Logo by <a 94href="http://www.brightercreative.co.uk">Sam Fisher</a>.</p> 95 96</div> 97</div> 98 99</body> 100</html> 101
