This allows {HEAD ~ a user} to download {TAIL ~ only a difference} between quality levels, saving time and resources, rather than downloading the entire multimedia stream afresh 
This allows { HEAD ~ a user } to download { TAIL ~ only a difference } between quality levels , saving time and resources , rather than downloading the entire multimedia stream afresh
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH