Filter overlay
  Overlay a video source on top of the input.
    Inputs:
       #0: main (video)
       #1: overlay (video)
    Outputs:
       #0: default (video)
overlay AVOptions:
  x                 <string>     ..FV.... set the x expression (default "0")
  y                 <string>     ..FV.... set the y expression (default "0")
  eof_action        <int>        ..FV.... Action to take when encountering EOF from secondary input  (from 0 to 2) (default repeat)
     repeat                       ..FV.... Repeat the previous frame.
     endall                       ..FV.... End both streams.
     pass                         ..FV.... Pass through the main input.
  eval              <int>        ..FV.... specify when to evaluate expressions (from 0 to 1) (default frame)
     init                         ..FV.... eval expressions once during initialization
     frame                        ..FV.... eval expressions per-frame
  rgb               <boolean>    ..FV.... force packed RGB in input and output (deprecated) (default false)
  shortest          <boolean>    ..FV.... force termination when the shortest input terminates (default false)
  format            <int>        ..FV.... set output format (from 0 to 3) (default yuv420)
     yuv420                       ..FV.... 
     yuv422                       ..FV.... 
     yuv444                       ..FV.... 
     rgb                          ..FV.... 
  repeatlast        <boolean>    ..FV.... repeat overlay of the last overlay frame (default true)

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

