In short, the telescreens announced a victory for the country. As Oceania had defeated Eurasia, the telescreens specifically cried:
"Vast strategic maneuver - perfect co-ordination - utter control of the whole of Africa - bring the war within measurable distance of its end - victory - greatest victory in human history - victory, victory, victory."
This announcement is important for two reasons.
First, this demonstrates for the last time that the people are hearing a manipulated message. They are being taken advantage of by the power of propaganda.
Second, this statements offers incredible irony. A victory has just been achieved over Winston's life. He has just been won to the Party's ideology forever. His humanity has been defeated.
The reading audience understands that the Party's message will always offer hope, but never actually truly achieve the means of completely defeating another country. The countries depend on being at war with each other to keep their people under control.