Function mpv_render_context_set_parameter 

pub unsafe extern "C" fn mpv_render_context_set_parameter(
    ctx: *mut mpv_render_context,
    param: mpv_render_param,
) -> c_int

Attempt to change a single parameter. Not all backends and parameter types support all kinds of changes.

@param ctx a valid render context @param param the parameter type and data that should be set @return error code. If a parameter could actually be changed, this returns success, otherwise an error code depending on the parameter type and situation.