Filter maskedmerge
  Merge first stream with second stream using third stream as mask.
    slice threading supported
    Inputs:
       #0: base (video)
       #1: overlay (video)
       #2: mask (video)
    Outputs:
       #0: default (video)
maskedmerge AVOptions:
  planes            <int>        ..FV..... set planes (from 0 to 15) (default 15)

This filter has support for timeline through the 'enable' option.

