Split/cut/join

Hello,
I want to cut/split or join some .avi, .wmv, .rm files but everytime proces is too slow or too long with decresing video quality - comparing to stand-alone DVD rec (with HDD) when this action take only few minutes??:eek:
Why re-coding video files is necessary durin this process?

All the files have to be the same picture size and data rate and format to join them together. Audio too.