Techniques for adaptive QoS include selecting, based on one or more QoS criteria corresponding to a client, one or more given data items suitable for sending to the client in response to a query from the client. The one or more given data items are selected from a set of data items. One or more statistics are associated with the one or more data items. The one or more statistics are useable to modify which data items are included in the set of data items. The statistics may be used by removing unpopular data items, as determined by the statistics, from the set of data items in the communication system. Additionally, data items exceeding the one or more QoS criteria can be transcoded to create new data items meeting the one or more QoS criteria, and the new data items can be added to the set of data items in the communication system. Thus, the set of data items can be changed depending on current demand by users for particular data items.