Half-SBS (Side-by-Side). This is a common 3D format where the images for the left and right eyes are squashed horizontally to fit within a single 1080p frame.
The specific file format "1080p Half-SBS AC3" refers to a common digital encoding used for home 3D viewing: Resident Evil Afterlife 2010 3d 1080p Half-sbs Ac3 31 -2021-