Techniques are provided for optimizing quality in adaptive streaming, where information is obtained relating to encoding bitrates and content quality scores for content segments of a content stream. The content segments of the content stream are provided by a content server and downloaded by a computing device. For each content segment, an encoding bitrate is determined for downloading the content segment from the content server, where determining the encoding bitrate for a current content segment is based upon an estimated current network bandwidth, constraints of a buffer into which downloaded content segments are stored, and also upon quality scores associated with content segments within a selected horizon extending from the current content segment to a future content segment in the content stream at an endpoint of the horizon. Each content segment with the determined bitrate for the content segment is downloaded from the content server.