Filter overlay
  Overlay a video source on top of the input.
    slice threading supported
    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          0            ..FV....... Repeat the previous frame.
     endall          1            ..FV....... End both streams.
     pass            2            ..FV....... Pass through the main input.
  eval              <int>        ..FV....... specify when to evaluate expressions (from 0 to 1) (default frame)
     init            0            ..FV....... eval expressions once during initialization
     frame           1            ..FV....... eval expressions per-frame
  shortest          <boolean>    ..FV....... force termination when the shortest input terminates (default false)
  format            <int>        ..FV....... set output format (from 0 to 7) (default yuv420)
     yuv420          0            ..FV....... 
     yuv420p10       1            ..FV....... 
     yuv422          2            ..FV....... 
     yuv422p10       3            ..FV....... 
     yuv444          4            ..FV....... 
     rgb             5            ..FV....... 
     gbrp            6            ..FV....... 
     auto            7            ..FV....... 
  repeatlast        <boolean>    ..FV....... repeat overlay of the last overlay frame (default true)
  alpha             <int>        ..FV....... alpha format (from 0 to 1) (default straight)
     straight        0            ..FV....... 
     premultiplied   1            ..FV....... 

framesync AVOptions:
  eof_action        <int>        ..FV....... Action to take when encountering EOF from secondary input  (from 0 to 2) (default repeat)
     repeat          0            ..FV....... Repeat the previous frame.
     endall          1            ..FV....... End both streams.
     pass            2            ..FV....... Pass through the main input.
  shortest          <boolean>    ..FV....... force termination when the shortest input terminates (default false)
  repeatlast        <boolean>    ..FV....... extend last frame of secondary streams beyond EOF (default true)

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

