系统为CentOS 6.4，自己编译ffmpeg和众多解码器太痛苦了，yum方式安装ffmpeg的解码器很全，先用用看。

1、安装所需软件

yum install -y automake autoconf libtool gcc gcc-c++

2、安装第三方更新源

rpm -ivh http://apt.sw.be/redhat/el6/en/i386/rpmforge/RPMS/rpmforge-release-0.5.3-1.el6.rf.i686.rpm

3、安装ffmpeg

yum install ffmpeg ffmpeg-devel

会自动安装众多解码器，ffmpeg版本为0.6.5-1.el6.rf。看了下yum安装的解码器版本还不是很旧，但是ffmpeg版本较老。

4、测试一下
将一个.avi视屏转为.flv格式

ffmpeg -i Destination.avi -y -ab 56 -ar 22050 -r 15 -sameq test2.flv

转换前后两个文件的格式比较：
转换前

Destination.avi
   General
      Complete name : E:\PV\Destination.avi
      Format : AVI
      Format/Info : Audio Video Interleave
      Format/Family : RIFF
      File size : 79.5 MiB
      PlayTime : 4mn 1s
      Bit rate : 2754 Kbps
      StreamSize : 469 KiB
      Subject : doobie (2007)
      Writing application : VirtualDubMod 1.5.10.2 (build 2540/release)
      Writing library : VirtualDubMod build 2540/release
   Video #0
      Codec : XviD
      Codec/Family : MPEG-4
      Codec/Info : XviD project
      Codec profile : Streaming Video Profile/Level 1
      Codec settings/PacketBitStream : Yes
      Codec settings/BVOP : Yes
      Codec settings/QPel : No
      Codec settings/GMC : 0
      Codec settings/Matrix : Default
      PlayTime : 4mn 1s
      Bit rate : 2556 Kbps
      Width : 640 pixels
      Height : 480 pixels
      Display Aspect ratio : 4/3
      Frame rate : 29.976 fps
      Resolution : 8 bits
      Chroma : 4:2:0
      Interlacement : Progressive
      Bits/(Pixel*Frame) : 0.277
      StreamSize : 73.5 MiB
   Audio #1
      Codec : MPEG-1 Audio layer 3
      Codec profile : Joint stereo
      PlayTime : 4mn 1s
      Bit rate : 190 Kbps
      Bit rate mode : CBR
      Channel(s) : 2 channels
      Sampling rate : 48 KHz
      Resolution : 16 bits
      StreamSize : 5.47 MiB
      Writing library : Gogo (after 3.0)

转换后

test2.flv
   General
      Complete name : E:\PV\test2.flv
      Format : Flash Video
      File size : 45.0 MiB
      PlayTime : 4mn 1s
      Bit rate : 1564 Kbps
   Video
      Codec : Sorenson H263
      PlayTime : 4mn 1s
      Bit rate : 195 Kbps
      Width : 640 pixels
      Height : 480 pixels
      Display Aspect ratio : 4/3
      Frame rate : 15.000 fps
      Bits/(Pixel*Frame) : 0.042
   Audio
      Codec : MPEG-1 Audio Layer 3
      Bit rate : 55 bps
      Channel(s) : 2 channels
      Sampling rate : 22 KHz
      Resolution : 16 bits

参考资料：

http://www.rosoo.net/a/201205/16001.html