需要转码的理由千万种，所幸除了硬件转码之外，Linux平台还有很多开源工具可以借鉴，如该文章所示：
原文来自：9 Essential Free Linux Transcoders（http://www.linuxlinks.com/article/20120413211230621/Transcoders.html）
Transcoding is the process of the conversion of digital data (typically video and audio files) from one format to another. It involves extracting tracks from a digital media file, decoding the tracks, filtering, encoding, and then multiplexing the new tracks into a new container. Transcoding will reduce the quality of the tracks unless lossless formats are used.
There are many reasons to transcode media files. Some popular examples include the ability to convert files so that they are supported on a target device, and at the same time removing commercials, and reducing the file size. Whilst transcoding is a very CPU intensive task, modern processors such as the AMD Phenom X4 and Intel's Core i5 and i7 processors offer impressive conversion rates provided the transcoding software supports multi-core architectures.
There is a good range of open source software available on the Linux platform for transcoding digital data. One application not featured in this article but is worthy of a mention is Transmageddon. This video transcoder is built using the pipeline-based multimedia framework, GStreamer. Transmageddon is in an early stage of development.
注：ST的SDK2中就使用到了GStreamer，但是部分芯片提供了硬件转码的能力
This article highlights the finest open source transcoding applications for Linux. Individuals that are interested in making digital media available for playback on mobile phones, or make frequent use of Home Theatre software will find transcoding software to be invaluable. Transcoding helps to ensure there is universal access of multimedia content.
To provide an insight into the quality of software that is available, we have compiled a list of 9 of the finest transcoders. There is a mix of graphical and console based applications featured here. Hopefully, there will be something of interest for anyone wanting to transcode digital data.
Now, let's explore the 9 transcoders at hand. For each title we have compiled its own portal page, a full description with an in-depth analysis of its features, a screenshot of the software in action, together with links to relevant resources and reviews.
Transcoders
HandBrake Multithreaded video transcoder
dvd::rip Perl front end for transcode
OGMRip Application and a set of libraries for ripping and encoding DVDs
avconv Part of libav-tools; fork of FFmpeg
FFmpeg Multimedia player, server and encoder //推荐，但是要做的工作不少
Arista Graphical user interface for FFmpeg
transcode Utility to encode raw video/audio streams
Mencoder MPlayer's Movie Encoder
WinFF Graphical user interface for FFmpeg
Return to our complete collection of Group Tests, identifying the finest Linux software.