SFF is a wire transport format for font data, designed for efficient transfer, incremental delivery, and trivial subsetting.
To see the rendered specification, go here
glyph2sff.py is a simple Python script to convert a TrueType-contour
OpenType font to SFF, and optionally report on byte statistics:
$ python3 glyph2sff.py -s NotoSans-Regular.ttf
cmap(1640) + glyf(133689) + hmtx(9662) = 144991 bytes
loca(9668) + maxp(32) = 9700
SFF equivalent = 137687 bytes