In ASF/WMA files, Picard ignores ReplayGain tags, so these are lost upon saving.
For instance, foobar2000 generates RG2 WMA tags as follows:
These should probably be checked for in a case-insensitive manner, since the ReplayGain 2.0 proposal specifies them to be uppercase but foobar and others use lowercase instead.
I plan to add ASF/WMA replaygain tagging support to loudgain, and the usual workflow is to replaygain the files, then use Picard to tag and move them into the final library. So it would be great if the RG info wouldn’t get lost in the process.
While you are at it, you might also please include the following tags loudgain might generate, so those won’t get lost either:
For FLAC, Ogg Vorbis, and MP3 this already works fine (i.e., Picard shows them and won’t remove them).