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                       ..F.A... select frame
     add                          ..F.A... add new metadata
     modify                       ..F.A... modify metadata
     delete                       ..F.A... delete metadata
     print                        ..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                     ..F.A...
     starts_with                  ..F.A...
     less                         ..F.A...
     equal                        ..F.A...
     greater                      ..F.A...
     expr                         ..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.

