From BlogCritics:
posted by Iain: One thing that can dramatically change the time to write ID3 tags, is if there is a format change. ID3 v1 tags are or fixed length, so if you alter the data you only have to rewrite the tag. However, if you start adding additional info such as in V1.1 tags or V2.3 tags (not sure what itunes uses) - then the tag suddenly becomes longer. At this point instead of just rewriting the tag the program has to rewrite the whole file to disc - this takes more time. This may account for the difference in write times you are experiencing. I suspect that Itunes is converting the tags.This is in response to my post about slow ID3 tag editing in iTunes. This clearly is the reason for it. I just checked it myself, I edited a MP3 with v 1.0 tag and added info that requires v 2.3 tags and it took much longer. Thanks Iain this answers my question.
