This is very easy and takes only a couple of minutes...

You have to use TMPGEnc12 or similar to this.

Go to files...Mpeg tools

Now click on the tab "Join", select MPEG-1,MPEG-2, or whatever you're dealing with. Now click "Add" and select your file.

Now double-click on the filename that you put on list. Here put in the Start and End point. Then click all the OK's and wait a minute for it to recreate the file.