Optional
'hstack' = side by side, 'vstack' = top/bottom, 'xstack' = grid layout
For xstack: grid columns (e.g. 2 for 2×2). Default: ceil(sqrt(n))
Extra output options e.g. ['-preset', 'ultrafast']
'hstack' = side by side, 'vstack' = top/bottom, 'xstack' = grid layout