epgs organize and present ( e . g ., by time or topic ) upcoming video program content . as cable and satellite services increasingly have hundreds of channels , such guides become essential . epgs are detailed in a variety of patents , including many assigned to gemstar and starsight , including u . s . pat . nos . 6 , 216 , 265 , 6 , 118 , 492 , 6 , 133 , 909 , 6 , 144 , 401 , 6 , 167 , 188 , 6 , 247 , 176 , 6 , 151 , 059 . in typical epg systems , a service provider ( e . g ., tv guide ) collects programming information from national , network and local program sources , and compiles it into a database . the database is indexed by geography and delivery source ( e . g ., portland oreg . ; at & amp ; t cable ). once a user &# 39 ; s location and delivery source is known , the database can be queried to identify programming that is upcoming , e . g ., for the next two hours . this data is typically presented in tabular ( grid ) form on the user &# 39 ; s video screen . advertising and other information may be presented with the epg data on the screen . epg data is presently conveyed to the consumer for display on - screen through “ out - of - band ” techniques , such as the vertical blanking interval in analog video . some systems have dedicated channels through which such data is presented . one drawback of such systems is their reliance on time - of - day as the key by which program schedules are determined . if a sports game runs late , or if breaking news forces an interruption in normal programming , the epg does not reflect the change . in accordance with one aspect of the present invention , watermark data identifying a program is decoded from incoming video . this information is then checked against program identification data in the epg and , if a discrepancy is noted , then a change in the programming is indicated on the displayed epg . consider superbowl sunday . the epg database may indicate that a superbowl broadcast on channel 2 is scheduled to end at 5 : 00 p . m . at 5 : 15 , a watermark is decoded from channel 2 and conveys an identifier associated with the superbowl , indicating that the superbowl program has run past its originally - allotted time . the epg can update its entry for the superbowl , extending its ending time to 5 : 15 ( the current time ), 5 : 30 ( the next half - hourly interval ), or otherwise mark it as changed . data for subsequent programming on that channel can likewise be treated as changed ( e . g ., by pushing back all programming 15 minutes , or to the next half - hourly interval , or otherwise ), and displayed in the epg accordingly . continuing this scenario , assume the superbowl broadcast ends at 5 : 20 . this ending time can be detected by failure to detect the superbowl - identifying watermark from program material on channel 2 for a predetermined interval , such as 5 minutes . at 5 : 30 , a new watermark id is detected — this one corresponding to the program originally scheduled for broadcast at 5 : 00 . in this case , the database can shift by 30 minutes the expected times of the 5 : 00 program , to 5 : 30 . viewers who refer to the epg at 5 : 35 will thus be presented with a timetable that accurately reflects the currently available programs . the expected timing of future programs can also be shifted in the epg database and display , with the service provider deciding how far out in time to continue this shift . certainly by midnight , for example , the programming would be expected to return to its originally scheduled timing , with some compensating program change ( e . g ., an abbreviation of the evening news ) making up for the superbowl overrun . in some embodiments , the epg interface presented to the user indicates that programming times for a particular channel are uncertain . in the example just given , for example , a graphical display of a program grid for channel 2 may be highlighted in yellow from 6 : 00 p . m . until midnight , indicating that a change has made precise air - times uncertain . as each half - hourly slot arrives , however , the detection of a watermark from the video then being sent permits at least the currently - available programming to be accurately displayed . ( of course , a variety of other techniques can be used to indicate schedule uncertainty , other than yellow highlighting . distinctive text presentation within the grid ( e . g ., italics ), special effects ( e . g ., flashing text or background color ), textual alert messages , and a great variety of other arrangements can be used to alert the viewer to the uncertainty .) in addition to indicating uncertainty in the program schedule , the epg presentation can also be altered to indicate that program times have been shifted from their expected values ( i . e ., certain times , but different ). again , a variety of user interface techniques can be used to signal this fact to viewers ( including techniques detailed above ). many vcrs , and essentially all personal video recorders ( pvrs ), rely on epg data to set start and stop times for recording functions . these devices can respond to watermarks , and / or epg information that is updated by reference to watermarks , to capture the desired program — regardless of program delays . assume that the 5 : 00 program following the superbowl on channel 2 is seinfeld , and the user has earlier specified that seinfeld ( 30 minutes ) should be recorded . at 5 : 00 , the recording commences . soon , however , the watermark data reveals that seinfeld isn &# 39 ; t yet playing . out of abundance of caution , the device may continue to record . or it may stop after , e . g ., a five minute grace period , and try again , re - starting at the next half - hourly interval . or , after stopping , it may immediately resuming recording if a seinfeld watermark is detected between 5 : 05 and 5 : 30 . if the device does not stop , but records continuously from 5 : 00 onward , it may continue until 30 minutes after a seinfeld - identifying watermark is first identified . thus , if seinfeld starts at 5 : 20 , the device will continue to record until 5 : 50 ( and optionally for a brief interval after that time ). if a seinfeld watermark isn &# 39 ; t detected within a predetermined window , e . g ., 90 minutes , of the expected air - time , the recording device may conclude that the seinfeld broadcast has been canceled ( avoiding recording of hours of unwanted programming ). in other embodiments , the stop time for a recording isn &# 39 ; t set by reference to epg data , or by reference to a known interval ( e . g ., 30 minutes ) after a start time . instead , the device stops only when a watermark identifying a desired program is no longer detected . ( here , as elsewhere , “ no longer detected ” typically requires absence of detection for a period of several minutes , to account for commercials and other interruptions that may not convey the watermark of the desired program .) if the recording device began recording at 5 : 00 , it captured part of the superbowl broadcast . rather than save this unwanted program material , it may be deleted . in pvrs , and other devices with digital storage , the storage space allocated to the unwanted programming can simply be marked as un - used by the desired program , and returned to the pool of available storage . in one such embodiment , recorded programming is discarded until a time a predetermined interval ( e . g ., 90 seconds ) before first detection of the seinfeld - identifying watermark . in other arrangements , instead of deleting the non - seinfeld program , it may be retained in storage . by reference to the updated epg data , or the watermark , the unwanted programming can be identified as the end of the superbowl . this information can be logged in the device &# 39 ; s index of recorded material , together with an identification of its length , and optionally the start and stop times of the original broadcast . ( other information , such as the location of the superbowl video data in the device &# 39 ; s file structure can also be maintained , but such information is typically transparent to the user .) when a table of recorded contents is presented to the user on - screen , the superbowl excerpt can be included among the listings — possibly set - off by distinctive ui presentation to indicate that it was an unintended capture . when the user is first presented with this unintended program capture , the system may ask the user whether it should be retained or deleted . the system may have a default option , e . g ., that unless the user acts to preserve the accidentally - captured video , it is deleted . in tape - based systems , if recording started at 5 : 00 , and at 5 : 25 the watermark corresponding to the recorded program still indicates a non - seinfeld program , the tape may be automatically rewound to the point where the 5 : 00 recording commenced . then , at 5 : 30 , recording can commence anew , on the possibility that seinfeld has been shifted to the next half - hourly slot and will be properly captured by recording from 5 : 30 to 6 : 00 . apart from accurately presenting program information , and correctly recording desired programs , watermarking can be employed in connection content security and authentication . consider the delivery of pay per view ( ppv ) content . the ppv content may have usage rules associated with it . these rules may , e . g ., disallow recording , or fast forwarding , or rewinding , or pausing , etc . these usage restrictions may be conveyed by out - of - band or virtual channels , such as data transmitted prior to the video program , or during the vertical blanking interval , or in packet headers . in accordance with certain embodiments of the present invention , watermarks are used to represent this information . for example , a video signal can include a watermark with an eight bit payload . the first bit , if set to “ 1 ,” can indicate no copying . the second bit , if set to “ 1 ,” can indicate one copy permitted . the third bit , if set , can indicate pausing is permitted . the fourth bit can correspond to rewind permission , the fifth to fast forward permission , the sixth can indicate that any copy must be made on a certain type of medium ( e . g ., a local pvr ), the seventh can indicate that any copy must be stored in encrypted form , etc . ( if copy - once is permitted , the video can be modified during the permitted copying operation to signal that no - more - copies are authorized . this may be done , e . g ., by applying a further watermark to the signal .) in still other embodiments , watermarks can be used in bandwidth optimization strategies to provide augmented information , or programming , to a consumer . consider a consumer who is interested in motorcycling . this preference may have been specified explicitly by the consumer , or may have been inferred through his behavior ( e . g ., his observed history of linking to on - line resources relating to motorcycles ). the topic of motorcycling may correspond to a particular 16 bit identifier in a subject matter index ( allowing 64 thousand subjects ). during hours when the pvr is not being actively used , it may scan through all channels looking for material that is coded with the motorcycle subject code ( perhaps among several others ). if such material is encountered , it is recorded , and a corresponding entry is made in the pvr &# 39 ; s local table of contents . when the consumer next uses the device , he can see that a program of potential interest has been recorded . the same technology can be used with advertising . advertising can be topically coded to identify the subject matter . if advertising is encountered having the motorcycle subject code , it can be captured and locally stored for possible later display . in this case , the presentation of the advertising can be requested by the user ( as with any other recorded program ), or the captured advertisement can be inserted in a commercial slot in other video programming ( perhaps supplanting another commercial that is not as likely to capture the consumer &# 39 ; s interest ). such encoding of video content with subject - indicating codes is limited by factors such as lengths of the codes , robustness to compression / decompression and other distortion , video degradation , and other factors . in one system , a watermark with an 80 bit payload can be encoded in video , permitting recovery of 5 different content codes every , e . g ., 30 seconds . the same content codes can be repeated every 30 seconds . or , by repeating them less frequently , more codes can be conveyed ( e . g ., codes 1 - 5 in time 0 - 30 seconds ; codes 6 - 10 in time 30 - 60 seconds , codes 1 - 5 in time 60 - 90 seconds , etc .). of course , this watermark may be overlaid or interleaved together with other watermarks conveying other information . instead of conveying absolute subject matter codes , each video excerpt can convey a unique id that is used to access associated meta data in a data store . the data store may be local ( e . g ., downloaded to a set - top box periodically ), or remote ( e . g ., at a cable head - end or elsewhere ). thus , a seinfeld program may have a single code . but when that code is used to access a corresponding database record with meta data , the record may reveal 10 subject matter codes ( e . g ., comedy , new york city , jerry seinfeld , motorcycling , episode 29 , episode title , etc .). different subject codes ( or unique ids ) can be used for different portions of a video program . so a ninety second clip that relates to a motorcycle may be coded to identify this subject matter , without so - coding the remainder of a program . the different portions need not be just temporal portions . through object segmentation technology , such as is used in mpeg - 4 , different on - screen objects can be encoded with different watermark identifiers . thus , a motorcycle in that ninety second clip may be encoded with a watermark indicating its motorcycle subject matter , while a bmw automobile in the same scene may be encoded with a different watermark . in monitoring program material for desired codes , the consumer device can have a buffer in which the previous 15 seconds of video is always available . thus , if a desired watermark is detected , video from 15 seconds prior to the detection can be written to long - term storage — to account for possible latency in watermark detection . in a typical scenario , there may be 100 subject codes for which a consumer &# 39 ; s pvr is watching , corresponding to 100 subjects of potential interest to the consumer . as each watermark is detected , it is checked against this list and , if a match is found , the video is captured ( including the buffered 15 seconds prior to detection ) for later display . if the program material is watermarked with unique ids instead of literal subject matter codes , the consumer device can query a database for the corresponding subject matter codes , and record the content if a match with one of the 100 profiled subject matter codes is found . in some embodiments the database is maintained remotely , introducing a delay as the decoded codes are sent to the data , and the results relayed back . other approaches can mitigate this delay . for example , some ( or all ) of the database can be cached at the consumer premises . another approach is for the consumer device to periodically send its 100 searched - for subject matter codes to the database , which then returns a list of the unique id records for which the consumer device should be on the lookout ( i . e ., those having the subject matter codes that are searched for ). the watermark detection functions referenced above can take place at various different locations . in some embodiments , detection may take place at a device in the consumer home , such as in one or more of a set - top box , vcr , pvr , television monitor , etc . information from such detection , in some embodiments , may be related back up the chain of distribution ( e . g ., a neighborhood distribution node , cable head - end , cable control center , national epg database provider , etc .) or the detection can take place at any of the upstream locations . for example , a station through which all at & amp ; t cable signals destined for subscribers in multnomah and clackamas counties in oregon can monitor all those channels . in some applications , it is desirable to employ the watermark - based systems detailed above in connection with known prior art techniques . ppv usage data , for example , can be conveyed both in header data associated with encrypted content , as well as by watermark data . one data can be relied upon primarily ( e . g ., the header data ) and , if absent or apparently corrupted , the watermark information can be relied upon instead . as should be evident from the foregoing , certain embodiments of the invention contemplate that a unique watermark identifier is associated with each video program . the identifier may be generic to a class of programs ( e . g ., all seinfeld shows are identified by the same watermark ), or each different program may have a different id . in the latter case , the watermark payload may have plural portions . one portion may id a family of programs ( e . g ., seinfeld episodes ), and another portion may convey an id uniquely identifying a particular program in that family ( e . g ., episode 88 , “ the big salad ”). the watermark identifier can be used to access a corresponding database record where information about the identified program is stored . it may include the date the program was first broadcast ( e . g ., “ sep . 29 , 1994 ”), a synopsis of the program ( e . g ., “ jerry dates newman &# 39 ; s ex . george buys elaine a big salad from the coffee shop , when his girlfriend takes credit for buying it . george lets elaine know that it was him that bought that salad . show ends with kramer driving gendison &# 39 ; s white ford bronco down the interstate ( ala oj )”), rights - holder information , digital rights management information , copy control information , links to related programs , links to related merchandise , links to on - line resources including chat rooms and program archives , subject matter classification codes , etc . this database may be stored remotely from the user station , and remotely accessed by the user as necessary . or some or all of the database and contents can be kept ( or mirrored ) in a data store at the user &# 39 ; s premises ( e . g ., in a set top box ). such a database can be configured in accordance with a user profile , e . g ., specifying the class of programs to be detailed in the local database . or the remote database can provide the local database with information corresponding to watermark ids expected to be encountered in the next 7 days ( e . g ., during early morning hours when system traffic is otherwise low ). a local user database can include information provided by the user and not shared with a remote database , including private notes about likes / dislikes , etc . or information provided by the user ( including demographics and viewing habits ) can be passed to a remote database . such personal information in the remote database can be shared with other users , with a cable system operator , with the provider of the annotated database record , etc . the user may receive a fee in some circumstances for sharing such information . certain of the above - described methods are illustrated in fig1 - 9 . to provide a comprehensive disclosure without unduly lengthening this specification , the patents and applications cited above are incorporated herein by reference . having described and illustrated the subject technologies with reference to illustrative embodiments , it should be recognized that the invention is not so limited . for example , it will be recognized that the concepts detailed above can be implemented with various forms of watermarking technologies , and can be advantageously combined in straight - forward fashion with other content - delivery systems . moreover , it will be recognized that wherever in the prior art that vertical blanking interval - based data communications techniques were used , the same applications may be served instead by conveying such data through in - band video watermarking . further , it should be recognized that the particular combinations of elements and features in the above - detailed embodiments are exemplary only ; the interchanging and substitution of these teachings with other teachings in this and the incorporated - by - reference materials are also contemplated .