i download some unfinished mpg files from net and i can play in windows media player it'ok , and when i used virtualdub to do cutting it'show some error which related with invalid header or what...

then i used vcdgear to correct problem it show no error but when i play the output files it adding some another mpg portion at the around center and last part of that movie and the download files actually was 5mb and when it show it become 7mb ... how can this happen i used vcdgear-gui.