tag.addField ("COMPILATION", TL_STR(metadata.compilation()));
tag.addField ("DISCSUBTITLE", TL_STR(metadata.disc_subtitle()));
tag.addField ("DISCNUMBER", to_string (metadata.disc_number(), std::dec));
tag.addField ("COMPILATION", TL_STR(metadata.compilation()));
tag.addField ("DISCSUBTITLE", TL_STR(metadata.disc_subtitle()));
tag.addField ("DISCNUMBER", to_string (metadata.disc_number(), std::dec));