activating exec() but how ?

I think the only thing i have to do now is activating exec()

but i don´t know how i can say my server that exe should be start

is there anything in the php.ini for that ? in disabled functions there is nothing so thats not the key

i have full root and my own linux apache2 server but i don´t know where it is to say him that exe is ok

for ffmpeg.exe

can you please help me ?

and a question : now i have save mode off and i should be exe on only for dolphin , is that not a security risk ?

havn´t to do that until now for any other script

Ok - i install a programm like gallery2 on the domain, and it installt funtion say that exec() is enabled - so i don´t have to figure out how to activate it - but video processing with with dolphin is still not function