Filter blend
  Blend two video frames into each other.
    slice threading supported
    Inputs:
       #0: top (video)
       #1: bottom (video)
    Outputs:
       #0: default (video)
blend AVOptions:
  c0_mode           <int>        ..FV.... set component #0 blend mode (from 0 to 31) (default normal)
     addition                     ..FV.... 
     addition128                  ..FV.... 
     and                          ..FV.... 
     average                      ..FV.... 
     burn                         ..FV.... 
     darken                       ..FV.... 
     difference                   ..FV.... 
     difference128                ..FV.... 
     divide                       ..FV.... 
     dodge                        ..FV.... 
     exclusion                    ..FV.... 
     freeze                       ..FV.... 
     glow                         ..FV.... 
     hardlight                    ..FV.... 
     hardmix                      ..FV.... 
     heat                         ..FV.... 
     lighten                      ..FV.... 
     linearlight                  ..FV.... 
     multiply                     ..FV.... 
     multiply128                  ..FV.... 
     negation                     ..FV.... 
     normal                       ..FV.... 
     or                           ..FV.... 
     overlay                      ..FV.... 
     phoenix                      ..FV.... 
     pinlight                     ..FV.... 
     reflect                      ..FV.... 
     screen                       ..FV.... 
     softlight                    ..FV.... 
     subtract                     ..FV.... 
     vividlight                   ..FV.... 
     xor                          ..FV.... 
  c1_mode           <int>        ..FV.... set component #1 blend mode (from 0 to 31) (default normal)
     addition                     ..FV.... 
     addition128                  ..FV.... 
     and                          ..FV.... 
     average                      ..FV.... 
     burn                         ..FV.... 
     darken                       ..FV.... 
     difference                   ..FV.... 
     difference128                ..FV.... 
     divide                       ..FV.... 
     dodge                        ..FV.... 
     exclusion                    ..FV.... 
     freeze                       ..FV.... 
     glow                         ..FV.... 
     hardlight                    ..FV.... 
     hardmix                      ..FV.... 
     heat                         ..FV.... 
     lighten                      ..FV.... 
     linearlight                  ..FV.... 
     multiply                     ..FV.... 
     multiply128                  ..FV.... 
     negation                     ..FV.... 
     normal                       ..FV.... 
     or                           ..FV.... 
     overlay                      ..FV.... 
     phoenix                      ..FV.... 
     pinlight                     ..FV.... 
     reflect                      ..FV.... 
     screen                       ..FV.... 
     softlight                    ..FV.... 
     subtract                     ..FV.... 
     vividlight                   ..FV.... 
     xor                          ..FV.... 
  c2_mode           <int>        ..FV.... set component #2 blend mode (from 0 to 31) (default normal)
     addition                     ..FV.... 
     addition128                  ..FV.... 
     and                          ..FV.... 
     average                      ..FV.... 
     burn                         ..FV.... 
     darken                       ..FV.... 
     difference                   ..FV.... 
     difference128                ..FV.... 
     divide                       ..FV.... 
     dodge                        ..FV.... 
     exclusion                    ..FV.... 
     freeze                       ..FV.... 
     glow                         ..FV.... 
     hardlight                    ..FV.... 
     hardmix                      ..FV.... 
     heat                         ..FV.... 
     lighten                      ..FV.... 
     linearlight                  ..FV.... 
     multiply                     ..FV.... 
     multiply128                  ..FV.... 
     negation                     ..FV.... 
     normal                       ..FV.... 
     or                           ..FV.... 
     overlay                      ..FV.... 
     phoenix                      ..FV.... 
     pinlight                     ..FV.... 
     reflect                      ..FV.... 
     screen                       ..FV.... 
     softlight                    ..FV.... 
     subtract                     ..FV.... 
     vividlight                   ..FV.... 
     xor                          ..FV.... 
  c3_mode           <int>        ..FV.... set component #3 blend mode (from 0 to 31) (default normal)
     addition                     ..FV.... 
     addition128                  ..FV.... 
     and                          ..FV.... 
     average                      ..FV.... 
     burn                         ..FV.... 
     darken                       ..FV.... 
     difference                   ..FV.... 
     difference128                ..FV.... 
     divide                       ..FV.... 
     dodge                        ..FV.... 
     exclusion                    ..FV.... 
     freeze                       ..FV.... 
     glow                         ..FV.... 
     hardlight                    ..FV.... 
     hardmix                      ..FV.... 
     heat                         ..FV.... 
     lighten                      ..FV.... 
     linearlight                  ..FV.... 
     multiply                     ..FV.... 
     multiply128                  ..FV.... 
     negation                     ..FV.... 
     normal                       ..FV.... 
     or                           ..FV.... 
     overlay                      ..FV.... 
     phoenix                      ..FV.... 
     pinlight                     ..FV.... 
     reflect                      ..FV.... 
     screen                       ..FV.... 
     softlight                    ..FV.... 
     subtract                     ..FV.... 
     vividlight                   ..FV.... 
     xor                          ..FV.... 
  all_mode          <int>        ..FV.... set blend mode for all components (from -1 to 31) (default -1)
     addition                     ..FV.... 
     addition128                  ..FV.... 
     and                          ..FV.... 
     average                      ..FV.... 
     burn                         ..FV.... 
     darken                       ..FV.... 
     difference                   ..FV.... 
     difference128                ..FV.... 
     divide                       ..FV.... 
     dodge                        ..FV.... 
     exclusion                    ..FV.... 
     freeze                       ..FV.... 
     glow                         ..FV.... 
     hardlight                    ..FV.... 
     hardmix                      ..FV.... 
     heat                         ..FV.... 
     lighten                      ..FV.... 
     linearlight                  ..FV.... 
     multiply                     ..FV.... 
     multiply128                  ..FV.... 
     negation                     ..FV.... 
     normal                       ..FV.... 
     or                           ..FV.... 
     overlay                      ..FV.... 
     phoenix                      ..FV.... 
     pinlight                     ..FV.... 
     reflect                      ..FV.... 
     screen                       ..FV.... 
     softlight                    ..FV.... 
     subtract                     ..FV.... 
     vividlight                   ..FV.... 
     xor                          ..FV.... 
  c0_expr           <string>     ..FV.... set color component #0 expression
  c1_expr           <string>     ..FV.... set color component #1 expression
  c2_expr           <string>     ..FV.... set color component #2 expression
  c3_expr           <string>     ..FV.... set color component #3 expression
  all_expr          <string>     ..FV.... set expression for all color components
  c0_opacity        <double>     ..FV.... set color component #0 opacity (from 0 to 1) (default 1)
  c1_opacity        <double>     ..FV.... set color component #1 opacity (from 0 to 1) (default 1)
  c2_opacity        <double>     ..FV.... set color component #2 opacity (from 0 to 1) (default 1)
  c3_opacity        <double>     ..FV.... set color component #3 opacity (from 0 to 1) (default 1)
  all_opacity       <double>     ..FV.... set opacity for all color components (from 0 to 1) (default 1)
  shortest          <boolean>    ..FV.... force termination when the shortest input terminates (default false)
  repeatlast        <boolean>    ..FV.... repeat last bottom frame (default true)

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

