codecs and formats of digital media

A codec is a device or software that is used to compress or decompress a digital media file, such as a video or song.
encoder performs the compression (encoding) function
decoder performs the decompression (decoding) function

A file format is like a type of container. Inside the container is data that has been compressed by using a particular codec.
Assuming your media player supports cettain format, whether a file can be played on your pc depends on which codecs were used to compress the file and which codecs you have installed on your computer.

MPEG (Motion Picture Experts Group) is one of the biggest families in video codec, and it is the most common video format.
codecs 　 : MPEG-1/-2 、MPEG-4、WMV7/WMV8/WMV9、H.264, QuickTIme   |   AAC, MP3, WMA, PCM
formats 　: AVI,MOV,ASF,WMV,RMVB,MKV,MPEG,MP4                                  |   MP3,WMA,WAV,ASF,AAC

Ripping is extracting all or parts of digital contents from a container, such as rip music from CD to pcs