Filter drawtext
  Draw text on top of video frames using libfreetype library.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
drawtext AVOptions:
  fontfile          <string>     ..FV..... set font file
  text              <string>     ..FV..... set text
  textfile          <string>     ..FV..... set text file
  fontcolor         <color>      ..FV..... set foreground color (default "black")
  fontcolor_expr    <string>     ..FV..... set foreground color expression (default "")
  boxcolor          <color>      ..FV..... set box color (default "white")
  bordercolor       <color>      ..FV..... set border color (default "black")
  shadowcolor       <color>      ..FV..... set shadow color (default "black")
  box               <boolean>    ..FV..... set box (default false)
  boxborderw        <int>        ..FV..... set box border width (from INT_MIN to INT_MAX) (default 0)
  line_spacing      <int>        ..FV..... set line spacing in pixels (from INT_MIN to INT_MAX) (default 0)
  fontsize          <string>     ..FV..... set font size
  x                 <string>     ..FV..... set x expression (default "0")
  y                 <string>     ..FV..... set y expression (default "0")
  shadowx           <int>        ..FV..... set shadow x offset (from INT_MIN to INT_MAX) (default 0)
  shadowy           <int>        ..FV..... set shadow y offset (from INT_MIN to INT_MAX) (default 0)
  borderw           <int>        ..FV..... set border width (from INT_MIN to INT_MAX) (default 0)
  tabsize           <int>        ..FV..... set tab size (from 0 to INT_MAX) (default 4)
  basetime          <int64>      ..FV..... set base time (from I64_MIN to I64_MAX) (default I64_MIN)
  font              <string>     ..FV..... Font name (default "Sans")
  expansion         <int>        ..FV..... set the expansion mode (from 0 to 2) (default normal)
     none                         ..FV..... set no expansion
     normal                       ..FV..... set normal expansion
     strftime                     ..FV..... set strftime expansion (deprecated)
  timecode          <string>     ..FV..... set initial timecode
  tc24hmax          <boolean>    ..FV..... set 24 hours max (timecode only) (default false)
  timecode_rate     <rational>   ..FV..... set rate (timecode only) (from 0 to INT_MAX) (default 0/1)
  r                 <rational>   ..FV..... set rate (timecode only) (from 0 to INT_MAX) (default 0/1)
  rate              <rational>   ..FV..... set rate (timecode only) (from 0 to INT_MAX) (default 0/1)
  reload            <boolean>    ..FV..... reload text file for each frame (default false)
  alpha             <string>     ..FV..... apply alpha while rendering (default "1")
  fix_bounds        <boolean>    ..FV..... check and fix text coords to avoid clipping (default false)
  start_number      <int>        ..FV..... start frame number for n/frame_num variable (from 0 to INT_MAX) (default 0)
  ft_load_flags     <flags>      ..FV..... set font loading flags for libfreetype (default 0)
     default                      ..FV.....
     no_scale                     ..FV.....
     no_hinting                   ..FV.....
     render                       ..FV.....
     no_bitmap                    ..FV.....
     vertical_layout              ..FV.....
     force_autohint               ..FV.....
     crop_bitmap                  ..FV.....
     pedantic                     ..FV.....
     ignore_global_advance_width              ..FV.....
     no_recurse                   ..FV.....
     ignore_transform              ..FV.....
     monochrome                   ..FV.....
     linear_design                ..FV.....
     no_autohint                  ..FV.....

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

