Described herein is technology for, among other uses, performing playback of dynamic content using protocols designed for playback of fixed-length files. The technology involves strategically updating the duration of the content during playback under various conditions. During playback, as the playback position approaches the duration, the duration is refreshed. Also, during playback the rate at which the duration is increasing is used to predict the duration and thus smoothly report the duration to the user. Upon receiving a seek request, if the request is beyond the current duration, the duration will be refreshed to avoid unnecessarily limiting the seek request.