When trying to convert the replaygain to soundcheck values on mp4/m4a files, I first noticed that no field was written, but then I discovered that the ITUNNORM field is removed if it's already there to start with... I have been using the script below and its album gain equivalent on thousands of files before with no problem.
Any idea of what's happening? (I should probably try an older version of mp3tag and get back, and I will do that tomorrow...)
edit: Apparently the | symbol isn't doing what it used to anymore. I separated mp4 from the second step and added one more, and now it works...
edit 2: Noooo... if m4a extension is used, mp3tag is still not using the itunnorm field, or deleting it. Darn.