most common customFileSignatures should be built in, PDF & MP3 not working.

[ivanjeremic]

customFileSignatures: {
    'FFFB':'audio/mpeg',
    'FFF3':'audio/mpeg',
    'FFF2':'audio/mpeg',
    '494433': 'audio/mpeg'
  }

I tried PDF and MP3 and both don't work, it is hard to debug, I followed the docs of customFileSignatures but no successs.

I hope anyone can explain to me how we would add extra mime-types of other formats for example when they have the same hex as existing ones in the object already and objects only accept unique key.