Transcoding usually refers to compressed domain transcoding. This is the method used by programs like DVD Shrink and CloneDVD to compress DVD video. Technically transcoding means starting with encoded video and encoding it again. In other words, once the video is stored digitally, encoding to another format, or even re-encoding to the same format is transcoding.
Compressed Domain Transcoding
Compressed Domain Transcoding is used by many popular DVD backup programs. It's much simpler than encoding. Rather than recalculate all the information required by an encoder, a compressed domain transcoder simply removes information from the original video stream. This results in a loss of detail, and is generally considered inferior to using an encoder to compress video. However, the relatively high speed, low cost, and ease of use associated with compressed domain transcoders like DVD Shrink and CloneDVD has made them popular.
