I test 5 audio codec (flac, aac(.m4a), mp3, opus, vorbis(.ogg)), all of them have replaygain 2.0 tag. But replaygain just work for flac, mp3, and vorbis(.ogg), not for opus and aac(.m4a). I wonder why it is not work, because opus use vorbis comment same as flac and vorbis(.ogg), aac(.m4a) use ID3v2 same as mp3. I use rsgain to apply replaygain 2.0 tag.