Recording ingame

Oh god.. Since when recording is such a hassle?
I downloaded millions of record programs , all show me a black screen of zps when I watch them even though the game works completely fine..
Tried to record via console - record "filename".. But you can't convert with any program .dem lol....
Would someone mind helping me?
And no don't tell me to go to Google cause I've been trying to fix this with Google for an hour already..
Tried millions of file converters no one recognizes .dem...