I have an ipod mini and try to download the video I have taken with my iPod to my computer to release space on my ipod. Thank you.

I have an ipod nano 5 and try to download the video I have taken with my iPod to my computer to release space on my ipod.

I also have an iPhone and I am confused on how the synch will work as my iPhone 4S and iPod don't seem to have the same synch / amount of songs, etc ... at the moment. I am using one single computer and do not share my files. If I plug my iPod and synch it, will it erase my iTune library and take what is on my iPod?

Thank you for your help.

Laurence