mp4box on german windows handles "." as decimal character fine, i would use it always
also when remuxing from .avi or .mp4 to .mp4 you dont need to set the fps! setting the fps is only necessary when muxing raw streams, which i guess is not done by staxrip
edit: another important feature might be chapters, which you can set via
-chap chapters.txt
the chapterformat supported by mp4box is, next to others, the well known "ogm format"
edit2: :name="english audio 5.1" or any other text the user wants
for extended characters, eg äöü, you need to beaware of
this