The BBC trust has demanded a "platform-agnostic" version of the iPlayer, which will be usable by people without Microsoft Windows.
In addition, the content will be syndicating to other internet operators - such as Google.
But the 13-week series stacking option will only apply to serials not soaps, where a much tighter window will be used.
Aperiod of consultation mean a final decision by the beginning of May.
BBC Trustee Diane Coyle told Broadcast: "The BBC Trust has a duty to ensure the public receives value in return for paying the licence fee. Our view is that the BBC's new on-demand services are likely to deliver significant public value, and should be allowed to proceed, but subject to certain conditions in order to reduce the potential negative market impact. In representing the public interest, the Trust's duty includes ensuring that the BBC does not adversely affect the market by reducing choice for licence fee payers. In reaching our decision, the Trust has therefore taken account of both the potential public value added and the potential negative market impact. We concluded that a number of modifications to the BBC's proposals are necessary to deliver the greatest value to the public."