Many suggestions of improvement

[Selur]

Nowadays, I would recommend to use openGOP instead of a fixed gop size unless you have some ancient hardware or software decoder.
When using a fixed gop, the idea of fps*10 was to find a balance between compression gain and keeping the content faster seekable for old hardware.
Remember this is only the max value (assuming the encoder inserts gops dynamically, which most modern encoders do, unless told otherwise).

Reasons (I see) for closed gop nowadays are:
a. (old) hardware or software compatibility
b. medium/format restriction (i.e. Blu-ray, UHD-Bluray)
c. you encode an intermedia file
d. you need a specific gop size (set min=max gop size) for some reason (i.e. academic)
if none of the above is a problem, use open gop.

Cu Selur

Ps.: uploaded a new dev which has an 'Adjust gop max to output fps' (to x264&265), have no use for it personally, but maybe it helps folks that do batch encoding with fixed gops.