If you ever decide to run an audio or video streaming server, it might be a good idea to learn about transcode. Essentially, transcode refers to the process of converting one multimedia file format to another. For example, you might convert a .wav audio file to an Mp3 file, or convert an Mpeg2 file to an H.264 file.
On a Linux server, transcode is a specific command that you can use to carry out the conversion process. It is available through most Linux distribution repositories. It is not the easiest software to use for conversion, but there are tutorials that can walk you through the process. For example, the transcode website gives examples for YouTube video encoding.
In addition to transcode, there are many other Linux encoders and converters that offer various features. Some of the most popular are mencoder, ffmpeg, and x264. Depending on your needs, you may get better results with a particular tool. There are also full suites that offer on the fly encoding and automatic conversion. These may be useful if you plan on uploading video files in bulk and need them converted and streamed without hand transcoding each one.