Revenue recognition - television serial production house

My client is a production house wherein they produce the content of television show for Doordarshan and submit it with invoice charging Rs. X amount per episode wise. Doordarshan in return releases Sanction order stating the episodes content have been approved with deductions (penalty) for difference in duration. Now my question is when should the revenue be recognised, when the client raises the bill upon completion of production of content ? or when the episodes are sanctioned ? or when the episodes are actually telecasted. Pls Advice?