Hexadecimal does not change the value, only the format in which the number is written.
(((hex)780/(dec)8))-(dec)31
and
(((dec)1920/(dec)8))-(dec)31
are equivalent, and both evaluate to 0xD1
(hex) or 209
(decimal).
It is actually byte 39 which is ambiguous in your question, because you did not specify whether 16:9
is 11 in decimal or hex (though I suspect it's 11 in hex)