The 3.98.1 release is a maintenance release over 3.98. Changes do not affect audio quality, but operational bug fixes only: - build system related: some fixes for mp3rtp and abx tools - encoder padding values were not correct when resampling was involved - frequency filtering API was broken; in case you want to use your own higher quality filtering method, it is now possible again to disable LAME buildin filters - ID3 tagging: --id3v1-only switch did not work anymore, fixed --tg <genre> improved, now it matches more often one of the ID3v1 genres, even when small spelling errors are involved --add-id3v2-size <n> is a new switch, it allows to define your own padding of n bytes.
