Filter ametadata
  Manipulate audio frame metadata.
    Inputs:
       #0: default (audio)
    Outputs:
       #0: default (audio)
ametadata AVOptions:
  mode              <int>        ..F.A.... set a mode of operation (from 0 to 4) (default select)
     select          0            ..F.A.... select frame
     add             1            ..F.A.... add new metadata
     modify          2            ..F.A.... modify metadata
     delete          3            ..F.A.... delete metadata
     print           4            ..F.A.... print metadata
  key               <string>     ..F.A.... set metadata key
  value             <string>     ..F.A.... set metadata value
  function          <int>        ..F.A.... function for comparing values (from 0 to 5) (default same_str)
     same_str        0            ..F.A....
     starts_with     1            ..F.A....
     less            2            ..F.A....
     equal           3            ..F.A....
     greater         4            ..F.A....
     expr            5            ..F.A....
  expr              <string>     ..F.A.... set expression for expr function
  file              <string>     ..F.A.... set file where to print metadata information

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

