Determining a quality of a media data stream including a sequence of data stream sections which transmit different media sections of a media content at quality-to-bitrate levels that vary across the media content, such as within the context of adaptive streaming, is configured to be more effective by deriving, from each data stream section, an identifier for the respective section, and by looking up, for each data stream section, a parameter set from a look-up table by means of the identifier derived for the respective data stream section, so that it is possible to aggregate the parameter sets and to determine the quality on the basis thereof.