What is the data parameter in obs_encoder_info.get_properties for?

[Xaymar]

At the moment, the get_properties function in obs_encoder_info has a useless "void *data" parameter. It's useless because it's only ever called with a value that isn't NULL in simple output mode and with QSV.
So what's it's true purpose? AAC in coreaudio-encoder uses it without checking if it's valid too.