Help with transcoder options

Please help with to configure stream process for adaptive or multibitrate live using hw=nvenc? Please show and example .
This line doesn’t work:
vb=700k hw=nvenc size=720x576 vb=1200k hw=nvenc size=1280x720 vb=copy ab=128k

It looks like a working configuration. Any errors in log file?

Yes, i made syntax mistake. Everything works now.