Encrypting file from source AEAD
I think you're confused here. The GCM algorithm has a 96 bit nonce, and fills the rest of the 128 bit block size with a 32 bit counter. So you have 2^32 full blocks at your disposal, or about 64 GiB. That's - uh - slightly more than 32 bits (well, OK, the counter starts at 2, so you'd have 48 bytes less than that, better keep it at 32 GiB or 48 GiB).