@ProVision:
The "-" at the end of the command-line is the input file. And here the special name "-" means
"read input from STDIN, rather than regular file". Since the input is pipe'd from the Avs2YUV process, this is absoloutely required!
But, as Ma said, there is no "--cu" option (see
here for details!). Seems like this is confusing x265's command-line parser, ultimaterly leading to the error that you are seeing. So please ty using "--ctu" instead.