a gio.output_stream.OutputStream to which to save the pixbuf
name of file format
name of options to set
values for named options
optional gio.cancellable.Cancellable object, NULL to ignore
a gio.types.AsyncReadyCallback to call when the pixbuf is saved
Saves pixbuf to an output stream asynchronously.
For more details see gdkpixbuf.pixbuf.Pixbuf.saveToStreamv, 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 gdkpixbuf.pixbuf.Pixbuf.saveToStreamFinish to get the result of the operation.