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<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><title>13.10.聽Preserving aspect ratio</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 - The Movie Player"><link rel="up" href="mencoder.html" title="Chapter聽13.聽Basic usage of MEncoder"><link rel="prev" href="menc-feat-extractsub.html" title="13.9.聽Extracting DVD subtitles to VOBsub file"><link rel="next" href="encoding-guide.html" title="Chapter聽14.聽Encoding with MEncoder"><link rel="preface" href="howtoread.html" title="How to read this documentation"><link rel="chapter" href="intro.html" title="Chapter聽1.聽Introduction"><link rel="chapter" href="install.html" title="Chapter聽2.聽Installation"><link rel="chapter" href="usage.html" title="Chapter聽3.聽Usage"><link rel="chapter" href="cd-dvd.html" title="Chapter聽4.聽CD/DVD usage"><link rel="chapter" href="faq.html" title="Chapter聽5.聽Frequently Asked Questions"><link rel="chapter" href="containers.html" title="Chapter聽6.聽Containers"><link rel="chapter" href="codecs.html" title="Chapter聽7.聽Codecs"><link rel="chapter" href="video.html" title="Chapter聽8.聽Video output devices"><link rel="chapter" href="audio.html" title="Chapter聽9.聽Audio output devices"><link rel="chapter" href="tv.html" title="Chapter聽10.聽TV"><link rel="chapter" href="radio.html" title="Chapter聽11.聽Radio"><link rel="chapter" href="ports.html" title="Chapter聽12.聽Ports"><link rel="chapter" href="mencoder.html" title="Chapter聽13.聽Basic usage of MEncoder"><link rel="chapter" href="encoding-guide.html" title="Chapter聽14.聽Encoding with MEncoder"><link rel="appendix" href="bugreports.html" title="Appendix聽A.聽How to report bugs"><link rel="appendix" href="bugs.html" title="Appendix聽B.聽Known bugs"><link rel="appendix" href="skin.html" title="Appendix聽C.聽MPlayer skin format"><link rel="appendix" href="history.html" title="Appendix聽D.聽History"></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">13.10.聽Preserving aspect ratio</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="menc-feat-extractsub.html">Prev</a>聽</td><th width="60%" align="center">Chapter聽13.聽Basic usage of <span class="application">MEncoder</span></th><td width="20%" align="right">聽<a accesskey="n" href="encoding-guide.html">Next</a></td></tr></table><hr></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="aspect"></a>13.10.聽Preserving aspect ratio</h2></div></div></div><p>
DVDs and SVCDs (i.e. MPEG-1/2) files contain an aspect ratio value, which
describes how the player should scale the video stream, so humans will not
have egg heads (ex.: 480x480 + 4:3 = 640x480). However when encoding to AVI
(DivX) files, you have to be aware that AVI headers do not store this value.
Rescaling the movie is disgusting and time consuming, there has to be a better
way!
</p><p>There is</p><p>
MPEG-4 has a unique feature: the video stream can contain its needed aspect
ratio. Yes, just like MPEG-1/2 (DVD, SVCD) and H.263 files. Regretfully, there
are few video players apart from <span class="application">MPlayer</span> that
support this MPEG-4 attribute.
</p><p>
This feature can be used only with
<a class="link" href="video-codecs.html#ffmpeg" title="7.1.1.聽FFmpeg/libavcodec"><code class="systemitem">libavcodec</code></a>'s
<code class="systemitem">mpeg4</code> codec. Keep in mind: although
<span class="application">MPlayer</span> will correctly play the created file,
other players may use the wrong aspect ratio.
</p><p>
You seriously should crop the black bands over and below the movie image.
See the man page for the usage of the <code class="systemitem">cropdetect</code> and
<code class="systemitem">crop</code> filters.
</p><p>
Usage
</p><pre class="screen">mencoder <em class="replaceable"><code>sample-svcd.mpg</code></em> -vf crop=714:548:0:14 -oac copy -ovc lavc \
-lavcopts vcodec=mpeg4:mbd=2:trell:autoaspect -o <em class="replaceable"><code>output.avi</code></em></pre><p>
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