Recently, I've made about adding arbitrary v2 tags to an mp3 file. As I had supposed, the function I needed was id3tag_set_fieldvalue. It works perfectly when you call it this way: id3tag_set_fieldvalue(gfp, "TIT2=Blahblah"), yet, it is unclear to me how to write the COMM frame, since it requires an encoding field of 1 byte, a language field of 3 bytes, an arbitrary short description field ending with zero byte (which acts like an end-of-line symbol), and the comment per se. So, does anyone know how to use it to properly add COMM tags?

The problem is, actually, about how to pass a zero byte inside a string, or if there are any delimiters recognized by the function

Why don't you just use a designated function like id3tag_set_comment_latin1() or id3tag_set_comment_ucs2()? They take the language, description and content parameters directly and should produce a correct ID3 frame.

These functions are present in id3tag.* files in libmp3lame directory, but they don't seem to be compiled into library. Actually, even the id3tag.h isn't copied to standard include directory after running "make install", but if I do it manually, or include it from the source dir, there is an "undefined reference" run-time error upon calling these functions.