Mold, yeast, or something else

Hey everyone,

This is my first attempt at home brewing and I noticed some stuff at the top of my beer. The beer has been in primary for 4 days now and I’m a little paranoid that my first batch may be infected. Can anyone fill me in on what this is. Any help would be greatly appreciated!

Did you have active fermentation? Krauesen? Looks like trub floating on the surface along with some CO2 being released.