What exactly do you mean? You want to cut and paste certain pieces into one file, or just reduce the size?
If you just want to reduce size, I would go with megui. It has a steep learning curve, but it is muxing, so it looses the least amount of quality
possible. I regularly mux to MKV, sometimes cut down the size 3/4, with no visible reduction of quality on my screen.



and got a window(?) message that stated I needed 3gbs of system resources to
...and I don't remember the rest.. I'll have to re-start the program and see if it comes up again .. 