saveToStreamvAsync   
  open fun saveToStreamvAsync(stream: <Error class: unknown class>, type: String, optionKeys: List<String>? = null, optionValues: List<String>? = null, cancellable: <Error class: unknown class>? = null, callback: <Error class: unknown class>?)(source)
Saves pixbuf to an output stream asynchronously.
For more details see gdk_pixbuf_save_to_streamv(), which is the synchronous version of this function.
When the operation is finished, callback will be called in the main thread.
You can then call gdk_pixbuf_save_to_stream_finish() to get the result of the operation.
Since
2.36
Parameters
stream
a GOutputStream to which to save the pixbuf
type
name of file format
optionKeys 
name of options to set
optionValues 
values for named options
cancellable
optional GCancellable object, NULL to ignore
callback
a GAsyncReadyCallback to call when the pixbuf is saved