If you're a Linux user like me and are looking for simple methods to combine split files or split large files then look no further than lxsplit (http://lxsplit.sourceforge.net/).
Step 1: Open terminal
Step 2: Install lxsplit, i.e. type 'sudo apt-get install lxsplit'
Step 3: Type 'lxsplit -j filename.mp4.001'
And you're done!
