The invention comprises a videoconference server (2) comprising: —an audio processing module (9) configured to, ∘calculating an average audio processing delay of processing audio packets intended to the second client device, in order that the second client device may synchronize a received video packet with the associated received audio packet, —a video router (10) configured to: ∘duplicate the video packet and temporarily store the duplicated video packet, ∘receive a retrieving request from the second client device (4) for retrieving a lost video packet, ∘retrieving the duplicated video packet associated with the identification information in the video buffer (17).