i have 2 videos of format .m4v encoded for my ipod touch i want to combine these 2 videos keeping there previous attributes same.how can i do it?

Which "attributes?"

bitrate,resolution etc.

You need to use or create a project setting profile that matches your videos. Then, it appears you need to do the same for the render profile. These things can be shared on this website and then retrieve from with kdenlive under the Settings menu. I see some render profiles for iPod, but they are not verified correct or working. The user community could use a bit more help and contribution in this area.