I just realized, that Helium stores the replay gain values in APE tags.
I know that's the default for mp3gain to store these values, but it's possible to use ID3v2 instead by using the command option "/s i".
I don't like to get another tag just for replay gain and all my previously tagged files (replay gain calculated by foobar2000) have these stored in ID3v2 too.
This involved a bit more than just changing the parameters in the call, a new tag-frame needs to be supported and used in various scenarios
Hmm, new tag frames? So mp3gain uses other frames than foobar2000 does?
MP3Gain uses the RVA2 frames which is currently not used. APE frames or ID3v2 TXXX frames are currently only supported.