layerInstructions
Instructions that specify how to layer and compose video frames from source tracks.
Declaration
var layerInstructions: [AVVideoCompositionLayerInstruction] { get }Discussion
Tracks are layered in the composition according to the top-to-bottom order of the layerInstructions array; the track with trackID of the first instruction in the array will be layered on top, with the track with the trackID of the second instruction immediately underneath, and so on.
If the property value is nil, the output is a fill of the background color.