1. A system for adaptive-rate content streaming of video playable on an end user station, the system comprising:a storage device to store a plurality of different copies of a same single video, each of the different copies encoded at a different bit rate and each of the different copies divided into a plurality of streamlets that collectively store data capable of playback of the entire single video but that individually store data to playback only a portion of the single video that starts at a unique start time during playback and that has a duration that is less than the entire playback duration of the single video, wherein the start times of the streamlets are the same for the different copies of the single video such that the streamlets with the same start times from the different copies independently represent the same portions of the single video, and
a web server configured to:
receive, for a each start time during playback of video, at least one stream let request over one or more network connections from the end user station to retrieve a streamlet storing a portion of the video starting at that start time from a currently selected one of the different copies, wherein the at least one streamlet request from the one or more end user stations includes a request for a currently selected one of the different copies dependent upon ongoing determinations to shift the playback quality to a higher or lower quality one of the different copies, wherein shifts in playback quality occur at the start times;
retrieve from the storage device the requested streamlet from the currently selected one of the different copies; and
send the retrieved streamlet from the currently selected one of the different copies to the requesting end user station over the one or more network connections.