I found the casting information of the local player using the following offsets starting from the unit's base (tested as priest):
(Version 1.13.2)
CastingStartTime (int32): 0x19B8
CastingEndTime (int32): 0x19BC
CastingSpellId (int32): 0x1968
The time is relative to the wow tickcount using QueryPerformanceCounter.
However I didnt manage to find any casting information of other units besides myself.
Also the wow api UnitCastingInfo doesnt seem to exist in the current classic dump.
I would appreciate if anyone can help me. An Ida function or function signature would be fine as well.
Thank you for your time.