PROSAGA码农传奇-ffmpeg-使用ffmpeg将音频文件转换为mp3

我需要使用ffmpeg将音频文件转换为mp3。当我将命令写ffmpeg -i audio.ogg -acodec mp3 newfile.mp3为时，出现错误：
<pre><code>FFmpeg version 0.5.2, Copyright (c) 2000-2009 Fabrice Bellard, et al.
 configuration: 
 libavutil 49.15. 0 / 49.15. 0
 libavcodec 52.20. 1 / 52.20. 1
 libavformat 52.31. 0 / 52.31. 0
 libavdevice 52. 1. 0 / 52. 1. 0
 built on Jun 24 2010 14:56:20, gcc: 4.4.1
Input #0, mp3, from 'ZHRE.mp3':
 Duration: 00:04:12.52, start: 0.000000, bitrate: 208 kb/s
 Stream #0.0: Audio: mp3, 44100 Hz, stereo, s16, 256 kb/s
Output #0, mp3, to 'audio.mp3':
 Stream #0.0: Audio: 0x0000, 44100 Hz, stereo, s16, 64 kb/s
Stream mapping:
 Stream #0.0 -> #0.0
Unsupported codec for output stream #0.0
</code></pre>我还运行了以下命令： <code>
 ffmpeg -formats | grep mp3
</code> 得到这个回应：
<pre><code>FFmpeg version 0.5.2, Copyright (c) 2000-2009 Fabrice Bellard, et al.
 configuration: 
 libavutil 49.15. 0 / 49.15. 0
 libavcodec 52.20. 1 / 52.20. 1
 libavformat 52.31. 0 / 52.31. 0
 libavdevice 52. 1. 0 / 52. 1. 0
 built on Jun 24 2010 14:56:20, gcc: 4.4.1
 DE mp3 MPEG audio layer 3
 D A mp3 MP3 (MPEG audio layer 3)
 D A mp3adu ADU (Application Data Unit) MP3 (MPEG audio layer 3)
 D A mp3on4 MP3onMP4
 text2movsub remove_extra noise mov2textsub mp3decomp mp3comp mjpegadump imxdump h264_mp4toannexb dump_extra
</code></pre>我猜未安装mp3编解码器。我在正确的轨道上吗？