BO2 is old and loves single-core performance. Go to Task Manager > Details > t6mp.exe > Set Priority > .
Or use a config file edit: Set seta split_screen "1" and seta scr_splitscreen "1" in config_mp.cfg . black ops 2 4 player split screen pc
: Most current methods require the Steam version of the game. Controllers BO2 is old and loves single-core performance