Merge multiple videos into single video file in c#.net

i using splicer to combine, but when export output file, size is very big

can you help me?

To my knowledge, this might be applicable using DirectShow, but if you are not deeply familiar with DirectShow, this will require hard work and long learning term. You can find more information about this here:
http://stackoverflow.com/questions/14301741/concatenate-video-files-directshow

I am currently using a multimedia toolkit (leadtools) that wraps DirectShow objects and provides higher-level controls and functions. I searched internet and found the following thread that might help:
http://support.leadtools.com/CS/forums/40399/ShowPost.aspx#40399
Note that the video files (to be merged) should have similar specs (Width, height, frame rate, etc...). Otherwise, you might need to unify the properties of these videos to merge them without problems.

Refer http://splicer.codeplex.com/