Windowing into compressed video without re-encoding

Windowingintocompressedvideowithoutre-enco dingKrishnaRatakondaIBMT.J.Watson ResearchCenter,YorktownHeights,NY10598ABSTRACTGiven a high resolution compressed video stream this pap er lo oks at the problem of extracting video from a smallwindowatanarbitrary, but staticlo cation, in compressed form, without having to either deco de the high resolutionvideostream or enco dethewindowstream.Sincestateofartvideo compressionalgorithms usemotioncom-p ensationinoneformortheother,compressedvideostreamcannotbeparsedtoobtainwindowwithout deco ding the high resolution stream to some extent and subsequent re-enco ding.On the other hand storingall p ossible windows as separate streams on the server is clearly infeasible, atleast as of to day, asitwould lead to anexplosion of the storage space requirement.In this pap er it will b e shown that with a comparatively small incrementinthe server's storage requirement,it is p ossible toobtain compressed window streams outofthehigh resolutionstream with minimal parsing, no deco ding or re-enco ding and little quality loss.Furthermore, ways to trade o thespacerequiredontheserverwithcompressioneciencyofwindowstreamwillbeshown.Althoughmain emphasis of this pap er will b e on showing whyand how this windowing problem is analytically feasible, resultsobtained from windowing into a standard de nition, MPEG-2 compressed video stream using one of the suggestedimplementations will b e shown to prove feasibility.Key words:windowed stream, compressed video, drift, video server, video streaming1.INTRODUCTIONWith the increasing usage of streaming video fo otage on the internet, there has b een a growing fo cus on technologieswhichenableb etteruserinteractivity.Manwebsitesnoprovidethesamevideofo otageatmultiplebitratesand/or resolutions so that users can cho ose the appropriate bit stream dep ending on the bandwidth of their internetconnection.Morerecentdevelopmentsincludecreatinghotspotsinthevideowhichusercanclicktoobtainrelevantinformation.Inthiscontext,giventhatypicalinternetconnectionsallowforonlyloresolutionvideotransmission, it will b e useful to provide the user withmeans of accessing an arbitrary but static p ortion of a lowresolution video at a higher resolution.Note that the di erence b etween such a stream, which will b e refered to asawindowstreamand a typical run of the mill internet video stream, is that the window stream allows the user toview theregion of interestwith the b est p ossible clarity.Many uses can b e found of sucha technology:for example,to catch the expression on a p erson's face ortoget a closer lo ok at some one in thecrowd;such detail canneverbeclearlyconveyed bytypicallowresolution internetvideo.Furthermore,creatingpre-determinedhotsp otsonthevideo limitsamountofuser interactivity and consequentlyhis/her interest in thepresentation.Thus itisimp ortant to b e able toarbitrarilyselect the region of interest.Akey assumption b ehind this pap er, which is almost universally true, is that the compressed low resolution videohas b een obtained from an original standard de nition (of the order of 72048030 frames/s) or high de nitionvideo (of the order of 1920108060 elds/s) which can b e made available in a compressed format on the videoserver connected to the internet.Given this assumption, the problem that I would like to address in this pap er canbestated as:\How can a compressedwindowstreamfroman arbitrary,butstaticlo cationinthehigh resolutionvideo stream b e generated on the y, without burdening the server with the computationally intensive tasks of eitherdeco ding the high resolution stream or enco ding the window stream."A trivial solution to this problem is to pre-compress window streams for all p ossible lo cations and window sizes and store them on the server.This is clearlyinfeasible, given to day's restrictions on server storage capacity.Email: ratakond@us.ibm.com, Telephone:914-945-2178.