<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>7.2. Audio codecs</title><link rel="stylesheet" href="default.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.73.2"><link rel="start" href="index.html" title="MPlayer - 电影播放器"><link rel="up" href="codecs.html" title="第 7 章 Codecs"><link rel="prev" href="video-codecs.html" title="7.1. Video codecs"><link rel="next" href="codec-importing.html" title="7.3. 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MPlayer skin format"><link rel="appendix" href="history.html" title="附录 D. History"><link rel="subsection" href="audio-codecs.html#swac3" title="7.2.1. Software AC-3 decoding"><link rel="subsection" href="audio-codecs.html#hwac3" title="7.2.2. Hardware AC-3 decoding"><link rel="subsection" href="audio-codecs.html#libmad" title="7.2.3. libmad support"><link rel="subsection" href="audio-codecs.html#hwmpa" title="7.2.4. Hardware MPEG audio codec"><link rel="subsection" href="audio-codecs.html#aac" title="7.2.5. AAC codec"><link rel="subsection" href="audio-codecs.html#amr" title="7.2.6. AMR codecs"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">7.2. Audio codecs</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="video-codecs.html">上一页</a> </td><th width="60%" align="center">第 7 章 Codecs</th><td width="20%" align="right"> <a accesskey="n" href="codec-importing.html">下一页</a></td></tr></table><hr></div><div class="sect1" lang="zh-CN"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="audio-codecs"></a>7.2. Audio codecs</h2></div></div></div><div class="itemizedlist"><p class="title"><b>The most important audio codecs above all:</b></p><ul type="disc"><li><p> MPEG layer 1/2/3 (MP1/2/3) audio (<span class="bold"><strong>native</strong></span> code, with MMX/SSE/3DNow! optimization) </p></li><li><p> Windows Media Audio 7 and 8 (AKA WMAv1 and WMAv2) (<span class="bold"><strong>native</strong></span> code, with <a class="link" href="video-codecs.html#ffmpeg" title="7.1.1. FFmpeg/libavcodec"><code class="systemitem">libavcodec</code></a>) </p></li><li><p> Windows Media Audio 9 (WMAv3) (using DMO DLL) </p></li><li><p> AC-3 Dolby audio (<span class="bold"><strong>native</strong></span> code, with MMX/SSE/3DNow! optimization) </p></li><li><p> AC-3 passing through sound card hardware </p></li><li><p> AAC </p></li><li><p> Ogg Vorbis audio codec (<span class="bold"><strong>native</strong></span> library) </p></li><li><p> RealAudio: DNET (low bitrate AC-3), Cook, Sipro and ATRAC3 </p></li><li><p> QuickTime: Qualcomm and QDesign audio codecs </p></li><li><p> VIVO audio (g723, Vivo Siren) </p></li><li><p> Voxware audio (using DirectShow DLL) </p></li><li><p> alaw and ulaw, various gsm, adpcm and pcm formats and other simple old audio codecs </p></li><li><p> Adaptive Multi-Rate (AMR) speech codecs </p></li></ul></div><div class="sect2" lang="zh-CN"><div class="titlepage"><div><div><h3 class="title"><a name="swac3"></a>7.2.1. Software AC-3 decoding</h3></div></div></div><p> This is the default decoder used for files with AC-3 audio. </p><p> The AC-3 decoder can create audio output mixes for 2, 4, or 6 speakers. When configured for 6 speakers, this decoder provides separate output of all the AC-3 channels to the sound driver, allowing for full "surround sound" experience without the external AC-3 decoder required to use the hwac3 codec. </p><p> Use the <tt class="option">-channels</tt> option to select the number of output channels. Use <tt class="option">-channels 2</tt> for a stereo downmix. For a 4 channel downmix (Left Front, Right Front, Left Surround and Right Surround outputs), use <tt class="option">-channels 4</tt>. In this case, any center channel will be mixed equally to the front channels. <tt class="option">-channels 6</tt> will output all the AC-3 channels as they are encoded - in the order Left, Right, Left Surround, Right Surround, Center and LFE. </p><p> The default number of output channels is 2. </p><p> To use more than 2 output channels, you will need to use OSS, and have a sound card that supports the appropriate number of output channels via the SNDCTL_DSP_CHANNELS ioctl. An example of a suitable driver is emu10k1 (used by Soundblaster Live! cards) from August 2001 or newer (ALSA CVS is also supposed to work). </p></div><div class="sect2" lang="zh-CN"><div class="titlepage"><div><div><h3 class="title"><a name="hwac3"></a>7.2.2. Hardware AC-3 decoding</h3></div></div></div><p> You need an AC-3 capable sound card, with digital out (S/PDIF). The card's driver must properly support the AFMT_AC3 format (C-Media does). Connect your AC-3 decoder to the S/PDIF output, and use the <tt class="option">-ac hwac3</tt> option. It is experimental but known to work with C-Media cards and Soundblaster Live! + ALSA (but not OSS) drivers and DXR3/Hollywood+ MPEG decoder cards. </p></div><div class="sect2" lang="zh-CN"><div class="titlepage"><div><div><h3 class="title"><a name="libmad"></a>7.2.3. <code class="systemitem">libmad</code> support</h3></div></div></div><p> <a class="ulink" href="http://www.underbit.com/products/mad/" target="_top"><code class="systemitem">libmad</code></a> is a multiplatform, integer (internally 24bit PCM) only MPEG audio decoding library. It does not handle broken files well, and it sometimes has problems with seeking, but it may perform better on FPU-less (such as <a class="link" href="linux.html#arm" title="12.1.3. ARM">ARM</a>) platform than <code class="systemitem">mp3lib</code>. </p><p> If you have a proper installation of <code class="systemitem">libmad</code>, <tt class="filename">./configure</tt> will notice and support for MPEG audio decoding via <code class="systemitem">libmad</code> will be built automatically. </p></div><div class="sect2" lang="zh-CN"><div class="titlepage"><div><div><h3 class="title"><a name="hwmpa"></a>7.2.4. Hardware MPEG audio codec</h3></div></div></div><p> This codec (selected by <tt class="option">-ac hwmpa</tt>) passes through MPEG audio packets to hardware decoders, such as the ones found in full-featured DVB cards and DXR2 adapters. Don't use it in combination with any other audio output device (such as OSS and ALSA) that isn't able to decode it (you will hear only white noise). </p></div><div class="sect2" lang="zh-CN"><div class="titlepage"><div><div><h3 class="title"><a name="aac"></a>7.2.5. AAC codec</h3></div></div></div><p> AAC (Advanced Audio Coding) is an audio codec sometimes found in MOV and MP4 files. An open source decoder called FAAD is available from <a class="ulink" href="http://www.audiocoding.com" target="_top">http://www.audiocoding.com</a>. <span class="application">MPlayer</span> includes a CVS snapshot of libfaad 2.1 beta, so you do not need to get it separately. </p><p> If you use gcc 3.2 which fails to compile our internal FAAD or want to use the external library for some other reason, download the library from the <a class="ulink" href="http://www.audiocoding.com/modules/mydownloads/" target="_top">download page</a> and pass <tt class="option">--enable-faad-external</tt> to <tt class="filename">./configure</tt>. You do not need all of faad2 to decode AAC files, libfaad is enough. Build it like this: </p><pre class="screen"> cd faad2/ sh bootstrap ./configure cd libfaad make make install </pre><p> Binaries are not available from audiocoding.com, but you can (apt-)get Debian packages from <a class="ulink" href="http://www.debian-multimedia.org/" target="_top">Christian Marillat's homepage</a>, Mandrake/Mandriva RPMs from the <a class="ulink" href="http://plf.zarb.org" target="_top">P.L.F</a> and Fedora RPMs from <a class="ulink" href="http://rpm.livna.org/" target="_top">Livna</a>. </p></div><div class="sect2" lang="zh-CN"><div class="titlepage"><div><div><h3 class="title"><a name="amr"></a>7.2.6. AMR codecs</h3></div></div></div><p> Adaptive Multi-Rate speech codec is used in third generation (3G) mobile phones. Reference implementation is available from <a class="ulink" href="http://www.3gpp.org" target="_top">The 3rd Generation Partnership Project</a> (free for private use). To enable support, download and install support libraries for <a class="ulink" href="http://www.penguin.cz/~utx/amr" target="_top">AMR-NB and AMR-WB</a> following the instructions on that page. Recompile MPlayer afterwards. </p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="video-codecs.html">上一页</a> </td><td width="20%" align="center"><a accesskey="u" href="codecs.html">上一级</a></td><td width="40%" align="right"> <a accesskey="n" href="codec-importing.html">下一页</a></td></tr><tr><td width="40%" align="left" valign="top">7.1. Video codecs </td><td width="20%" align="center"><a accesskey="h" href="index.html">起始页</a></td><td width="40%" align="right" valign="top"> 7.3. Win32 codecs importing HOWTO</td></tr></table></div></body></html>
