Atem ISO vs Program files are different length & out of sync

After switching to camera originals , one second of .mp4 file remains at the beginning of timeline.

I lined up the same take off of Atem and the ISO camera. Atem clip is longer by one second.

Also, the beginning and ending frames are totally different.

BMPCC4K cameras x 2, software version 8.1. Atem Mini pro iso, software latest version.

Braw is all i captured in camera. The iso files are sitting on the other side of a scaler and a frame sync, additionally h264 is 15 frame long GOP. The start and end frames will never be the same due to the immutable physical laws of the universe.

Good Luck