with mp3 it is the same as with gnutella after "the standart" everybody who thinks he's very smart includes his own headers...

in an mp3 file every frame can use another bitrate without something special. To check if a file VBR you can read two or three frame headers, if all use the same bitrate it is an CBR file...

some time ago, the Xing encoder used a "Xing"-Tag to supply the decoder with data, but no really good mp3-encoder uses the xing-engine (bad quality). You can reach a good quality with FHG IIS Layer3 encoder oder LAME... hope most people use them...?

you can get more info (with C++ Classes) here: http://home.swipnet.se/grd/mp3info/


CU