WO2011018433A1

WO2011018433A1 - Digital video recorder with linear recording buffer

Info

Publication number: WO2011018433A1
Application number: PCT/EP2010/061560
Authority: WO
Inventors: John Thomas Mcdole; Edward R. Grauch
Original assignee: Nagravision S.A.
Priority date: 2009-08-11
Filing date: 2010-08-09
Publication date: 2011-02-17

Abstract

A digital broadcast video recorder (10) with a linear event buffer (12) comprising a live broadcast event recording buffer (26) and at least one recorded broadcast event buffer (28), each buffer logically connected on a digital recording device (24), and a processor (16) with a buffer controller (22) configured to access the linear event buffer (12) for selective display of the broadcast event recorded in the buffers (26, 28) on a display device and for culling a recorded buffer upon commencing recording of a new broadcast event. A method of recording and culling live broadcast events is disclosed.

Description

DIGITAL VIDEO RECORDER WITH LINEAR RECORDING BUFFER

TECHNICAL FIELD

The present invention relates to apparatus and methods for digital recording of video broadcast events. More particularly, the present invention relates to digital video recorders configured to buffer live broadcast events while allowing the user to pause and rewind live broadcast events as well as buffered recorded broadcast events.

BACKGROUND OF THE INVENTION

Cable and satellite television services provide to subscribers a number of simultaneous broadcast events. The programs or broadcast events are accessible selectively through a control box associated with the subscriber's television. Each subscriber can display on his television a selected one of the live broadcast events.

To provide capability for time-shift viewing of live broadcast events, many control boxes include a digital video recorder (DVR) configured for circular buffering of the live broadcast. Time-shift viewing allows recording of a selected live broadcast for later viewing. Simultaneous recording and display of a live broadcast event also permits the subscriber to pause the live broadcast event (while the live broadcast event continues to be recorded). The subscriber can then rewind the recorded portion for re-view of a selected portion. The subscriber can continue viewing from the pause, or can advance through the recorded portion to catch up to the live portion, or return directly to the live portion being simultaneously recorded.

The DVR device provides the subscriber with flexibility in viewing of live broadcast events. The DVR device enables a subscriber to watch a selected live broadcast and record for later (time-shifted) viewing a second simultaneous live broadcast. Or, as noted above, the subscriber may "pause" a live broadcast event, for example, the subscriber is interrupted by another matter (a phone call, for example) or desires to re-view a portion of the live broadcast event (to re-hear a portion of audio and/or re-see a portion of the video). In that circumstance, the selected live broadcast event continues to be recorded during the live broadcast. The subscriber "pauses" or holds the live broadcast event. This involves continuing to record the live broadcast but the subscriber can "pause" the already recorded portion of the live broadcast. This holds the recorded portion at the moment of pausing (the moment of interruption). The subscriber can then rewind the recorded portion, re-play a portion of the recorded live broadcast event, and advance through the recording to catch up with the live broadcast, or continue watching the recording of the live broadcast.

While such time-shift viewing enables a subscriber to view later an event that was recorded, there are drawbacks to the DVR apparatus and method for buffering of the live broadcast event. Particularly, the recording buffer is of a limited duration. If the subscriber does not return to the recording timely, the buffer may become filled. The end of the buffer effectively reaches the "pause" point. The controller then effectively un- pauses the user-selected pause, so that recording of the then-current live broadcast event can continue. The controller then removes over time the recorded portion of the paused broadcast event from access by the subscriber by the continued recording of the then- current live broadcast event. Ultimately over the duration of the recording buffer, the entire remaining portion of the live broadcast event paused by the subscriber is removed. The subscriber no longer can watch that paused broadcast event as a time-shift event.

Accordingly, there is a need in the art for an apparatus and method for DVR time- shift recording of live-broadcast events that allow the subscriber to pause and rewind live broadcast events. It is to such that the present invention is directed.

SUMMARY OF THE PRESENT INVENTION

The present invention meets the need in the art by providing a time-shift digital broadcast video recorder with a linear event buffer comprising a live broadcast event recording buffer and at least one recorded broadcast event buffer, each of the live broadcast event recording buffer and the recorded broadcast event buffer capable of filling to a predetermined size and logically connected together in sequence on a digital recording device, and a processor with a buffer controller configured to provide access by a user to the linear event buffer for selective display of the broadcast event recorded in the live broadcast event recording buffer and the recorded broadcast event buffer.

In another aspect, the present invention provides a method of time-shifting digital broadcasts comprising the steps of:

(a) recording a live broadcast event in a live broadcast event recording buffer capable of filling to a predetermined size from a beginning point to an ending point of the live broadcast event after which the live broadcast event buffer becomes one of at least two recorded broadcast event buffers; (b) commencing the recording of a new live broadcast event in a new live broadcast recording buffer;

(c) culling a selected one of the recorded broadcast event buffers; and

(d) providing a user with a capability to mark either the live broadcast event recording buffer or at least one of the recorded broadcast event buffers during recording of the live broadcast event, whereby the marked buffer is prevented from being culled.

Objects, advantages, and features of the present invention will become apparent upon a reading of the following detailed description in conjunction with the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1 illustrates a schematic overview of the digital video recording apparatus according to an embodiment of the present invention.

Fig. 2 illustrates a chart of icons and descriptions of recording buffer and video recording apparatus status during exemplary operation of the digital video recording depicted in Figs. 3 - 10.

Fig. 3 illustrates a schematic view of the digital video recording apparatus in a first exemplary operation of recording a broadcast event in a time-shift recording buffer.

Fig. 4 illustrates a second schematic view in the first exemplary operation depicting the digital video recording apparatus recording a second event.

Fig. 5 illustrates a third schematic view in the first exemplary operation of the digital video recording apparatus.

Fig. 6 illustrates a schematic view in a second exemplary operation in which the digital video recording apparatus culls a buffer when recording a new broadcast event.

Fig. 7 illustrates a second schematic view in the second exemplary operation after the digital video recording apparatus culls a buffer when recording a new broadcast event.

Fig. 8 illustrates a schematic view in a third exemplary operation in which the digital video recording apparatus culls a buffer when recording a new broadcast event.

Fig. 9 illustrates a second schematic view in the third exemplary operation after the digital video recording apparatus culls a buffer when recording a new broadcast event. Fig. 10 illustrates a schematic view in a fourth example that depicts operation of the digital video recording apparatus over time.

Fig. 11 illustrates a display of metadata for broadcast events recorded by the digital video recording apparatus.

DETAILED DESCRIPTION

With reference to the drawings in which like reference numerals indicate like parts, Fig. 1 illustrates a schematic of a digital video recorder apparatus 10 configured to buffer live broadcast events while allowing a user to pause and rewind live broadcast events and recorded broadcast events recorded within a linear recording buffer generally 12. The apparatus 10 includes a processor 14 that includes memory and an operating system configured to implement a system that buffers live broadcast events while allowing the user to pause and rewind live broadcast events and recorded broadcast events.

The processor 14 communicates with a signal input stage 16 and a signal output stage 18. A signal arrives at the signal input stage 16 from a signal provider such as a cable or satellite video broadcast supplier. In one embodiment, a signal control box provided to the user by the signal provider includes the apparatus 10. The signal control box conventionally decodes signals from the signal provider. The signal output stage 18 drives a signal of an audio -visual event to an image display device such as a user's television 20. The processor 16 is configured with a buffer controller 22 that directs the allocation of recording space for the linear recording buffer 12. A hard drive 24 or other high speed, high capacity data storage device defines a memory device for the linear recording buffer 12. The linear recording buffer 12 includes a current live broadcast event recording buffer 26 and at least one broadcast event recorded buffer 28. The event recording buffer 26 receives the signal relative to the current live broadcasting event. The event recorded buffer 28 received the signal relative to a previous live broadcasting event.

As illustrated in Fig. 1, an embodiment of the present invention may have more than one event recorded buffer 28α ... 28/?.

The processor 16 is configured for user access and viewing of the contents of the recorded event buffer 28 as well as the recorded contents of the event recording buffer 26.

This includes the capability to rewind, fast rewind, pause, stop, forward, slow forward and fast forward through the signals recorded in the event recording and recorded buffers 26,

28. An active event buffer is one presented to the subscriber for viewing and controlling with these capability commands. The signal received from the event recording buffer 26 or the event recorded buffer 28 passes from the processor 16 though the output signal stage

18 to the television 20. The buffers 26, 28 are logically linked so that the processor can move between the event recording and recorded buffers 26, 28. The buffers 26, 28 do not have to be contiguous spaces on the hard drive 24. The buffer controller 22 allocates the current live broadcasting buffer 26, manages the prior event recorded buffer(s) 28, manages a prior paused event recorded buffer as discussed below, and culls a prior event recorded buffer 28 upon allocation of a new current live broadcasting recording buffer 26. The current live broadcasting recording buffer 26 is allocated when a new broadcasting event commences. Commencement occurs (a) when the digital video recorder apparatus 10 is first supplied with power (i.e., the apparatus 10 is off, and then turned on such as when turning on the television and the control box in order for the user to watch a live broadcast event), and (b) when a new event starts broadcasting to the control box by the signal provider. Upon commencement, the apparatus 10 records the digital signal of the current live broadcasting event in the event recording buffer 26.

The buffer controller 22 also manages the prior recorded buffer(s) 28. By this is meant the buffer controller 22 maintains information as to which buffer 28 is available to the user for display of recorded events. As discussed below, one of the buffers 28 can be paused by the user. This makes the particular buffer 28 "active" (as discussed below) and prevents the particular buffer 28 from being culled, or removed from access by the user, during operation of the apparatus 10. Finally, the buffer controller 22 culls, or removes access to, one of the event recorded buffers 28 upon commencement of a new current live broadcasting event. The exemplary embodiment culls the oldest non-active recorded buffer 28.

A broadcasting event correlates to a television program provided by the signal provider. Commencement of a new live broadcasting event occurs when the program commences and terminates when a subsequent program commences. Commencement also occurs when the user turns on the apparatus 10 (and it may be that the apparatus 10 is turned on after the television program has started.) The buffer controller 22 allocates a static buffer on the disk drive 24. Buffers are filled starting from an initial starting point (0 bytes) and continue to fill until either a rule-set or the occurrence of a new event. The event buffer reserved space is algorithmically enforced. The buffer can fill to a predetermined size sufficient to record the signals for the broadcasting event. The fixed size is defined at an initialization of the application implemented by the processor 16. The event buffer controller 22 enforces the size of the maintained buffers so that a buffer does not exceed the defined size. In an exemplary embodiment, the application prevents other file system space to remain out of or below the reserved space for event buffers. An alternate embodiment however creates pseudo partitions in the file system api, which reduces file system management demands. Typical television programs are of one-half hour and one-hour lengths; television movies are typically two to three hours; sports events are typically three to four hours. The static buffer is sized to accommodate most expected program lengths. A defined size for six hours recording buffer is sufficient in an exemplary embodiment of the present invention.

Upon commencement of a new live broadcasting event, the buffer controller 22 culls the oldest non-active event recorded buffer 28. A buffer 26, 28 that is subject of a pause command is "active" according to the present invention. Also, a buffer presenting to a user a broadcast event that is recorded in the buffer is also "active." Thus, if the presentation (play-head) is logically reading from a buffer, that buffer is active.

The buffer controller 22 manages the recording of the signal for the new live broadcasting event in the event recording buffer 26 and manages the recorded signal in the event recorded buffer 28. The user can operate the processor 16 to access and view the recordings in the event recording and recorded buffers 26, 28. The user can selectively rewind, fast rewind, pause, stop, forward, slow forward, and fast forward through the signals recorded in the event recording and recorded buffers 26, 28. The signal received from the event recording buffer 26 or event recorded buffer 28 passes from the processor 16 though the output signal stage 18 to the television 20. The buffers 26, 28 are logically linked so that the processor 16 can move between the event recording and recorded buffers 26, 28.

If a user selects to pause the broadcasting event being viewed in the event recording buffer 26 or event recorded buffer 28, that event buffer will not be culled as that buffer is "active". Rather, that buffer with the recorded signals will be retained for future access by the user. When the user "pauses" a broadcast event recorded in the event recorded buffer 28 (i.e., the user is viewing a completed broadcast event), the apparatus 10 will retain that buffer as an "active" buffer and continue recording the then-current live broadcast event in the event recording buffer 26. Upon completion of the then-current live broadcast event, the next live broadcasting event commences. The buffer controller 22 allocates a new recording buffer 26 and starts recording the signal in the new recording buffer. The former new event recording buffer 26 is then designated a recorded buffer 28. The buffer controller 22 culls the recordied buffers 28. For example, one of these recorded buffers 28 is "paused" and thus "active" and the other is not paused. The buffer controller 22 culls the oldest non-active one of the event recorded buffers 28.

When a user enters the "pause" command to the apparatus 10 while viewing a portion of the then current live broadcast event (which is being simultaneously recorded in the event recording buffer 26), the apparatus 10 will continue recording the live broadcast event in the buffer 26. Upon completion of the broadcast event, the next live broadcasting event commences. The buffer controller 22 allocates a new recording buffer 26 and starts recording the signal in the new recording buffer. The former live event recording buffer 26 is designated a recorded buffer 28. That newly designated recorded buffer 28 is also designated as "paused" and thus is active. The buffer controller 22 then culls the recorded buffers 28. In this example, one of these recorded buffers 28 is "paused" (and thus active), and the other is not paused. The buffer controller 22 culls the oldest non-active recorded buffer 28.

In an alternate embodiment, the buffer controller 22 first determines which of the oldest non-active recorded buffers 28 to cull before re-designating the live broadcast recording buffer 26 as a recorded event buffer 28 and allocating a new recording buffer 26 on the hard drive 24 in which the new broadcast event is recorded.

In an exemplary embodiment, the buffer controller 10 manages three event recording buffers: one live broadcasting event recording buffer 26 and two recorded broadcast event buffers 28. As explained above, the apparatus 10 may have momentarily an additional recorded broadcast event buffer 28 while the buffer controller 22 determines which buffer 28 to cull following commencement of a new live broadcast recording event buffer 26. In an exemplary embodiment, the buffers 26, 28 are sized to receive six hours of broadcast event signals.

As may be appreciated, the present invention provides a linear time-shift buffer that is unlike circular buffers (first-in, first-out) of the previous x time period (minute or hours) of broadcast television content. A circular buffer captures a fixed length of audio/video signals from the moment of first tuning a broadcast channel until the buffer duration limit is reached and the recording buffer then abandons the first-in signals as then current signals are recorded. That is, the end of the buffer moves forward in time.

In contrast, the apparatus 10 in the present invention preserves or buffers up to the N most recent broadcast events, OR the N-I most recent broadcast events plus the event that is currently PAUSED. The value of N and the maximum length of the buffered events are configurable by the native software.

If the user pauses the currently broadcast program, the user will remain paused in that location indefinitely as discussed above, until the user selects to make a change

5 relative to that event recording buffer. It is to be appreciated that the buffer in which the user is in, always remains valid except for extreme cases (for example, an emergency alert system broadcast or other interruptible event. In those circumstances, the processor tunes to the emergency broadcast message for display on the television but no recording buffer is used for simultaneous recording). The time-shift buffer will preserve that position in that

10 event even after the N-I most recent broadcast events have already been aired.

In the method of the present invention, all recorded broadcast events are presented to the user as a continuous series of events. The user is able to time-shift forwards and backwards between buffered events. The user can also select to save 30 the event in active presentation, saving it from being discarded or culled.

15 As new events are broadcast, the oldest, non-active buffer is discarded or culled.

In accordance with the present invention, the buffer controller 22 operates on buffer commencement and culling rules.

1) File size limit 40% / 40% / 20% of designated event buffer space. The event recording and recorded buffers 26, 28 can each occupy up to 40% of the space on the

20 disk drive 24 designated for event buffers, with a 20% margin for commencing a subsequent live broadcasting event. The buffer controller 22 will commence the recording of the new live broadcasting event and then determine which of the recorded event buffers 28 to cull.

2) File time limit (an exemplary embodiment of 6 hours is believed sufficient) 253) Event End Time

In an alternate embodiment, the user may select specific recorded events to save 30 for later viewing. This "save" feature differs from the "pause" feature discussed above. Broadcast recording events that are selected by the user to be "saved" are removed from consideration by the buffer controller 22 for culling according to the rule set for culling the 30 oldest, non-active event in a broadcast recording event buffer 28. The saved buffers 30 remain active to the user until N buffers are in use and the saved event is the oldest, non- active event; that is, all buffers 28 are "saved" or "active"; then the oldest "saved" buffer is culled. In an exemplary embodiment, the saved event buffer 30 that is culled is not deleted from the file system and can be accessed from outside of the event buffer controller 22. Also, saved buffers 30 do not count against the size requirements in the event buffer controller rule set. Saved buffers 30 are maintained in the queue for the convenience of time-shifting between buffers in a temporal fashion; when a saved buffer 30 is culled, the buffer is removed from the list but is not deleted from the file system as noted above.

It is to be appreciated that the signal input from the signal provider may be television input streams in analog or digital form, for example, National Television Standards Committee (NTSC) or PAL and Digital Satellite System (DSS), Digital Broadcast Services (DBS), or Advanced Television Standards Committee (ATSC), or in other standards as currently used or may be developed. Further, analog streams may be converted to Moving Pictures Experts Group (MPEG) format for internal manipulation. One of ordinary skill in the art will further understand an implementation can include parsing of signal streams into video and audio components with appropriate time stamp tracking for reassembly of the signal for display on the television. User control commands applied are conventional for viewing the recorded broadcast event (whether the live broadcast or previously recorded event) with at least the following functions: reverse or rewind (fast/slow), play (normal, fast and slow), forward (slow/fast), pause, reverse play (normal, fast, and slow), and stop.

EXAMPLES OF OPERATION

OF THE DIGITAL VIDEO RECORDING APPARATUS

Fig. 2 illustrates a Chart 1 of icons or symbols and associated descriptions depicting the status of the recording buffers 26, 28 during exemplary operation of the digital video recording apparatus as discussed below and illustrated schematically Figs. 3 - 10. Chart 1 lists icons or symbols and descriptions used in the following examples.

Example 1 - Channel Change & Pause

Figs. 3 - 5 illustrate schematic views of the digital video recording apparatus 10 in a first exemplary operation of recording a broadcast event in a time-shift event recording buffer 26. With reference to Fig. 3, the user tunes a new broadcast service and the time- shift event recording buffer 26 automatically activates. The digital video recording apparatus 10 records the broadcast event signals in the time-shift event recording buffer 26.

At some point during the live broadcast event, the user enters the "pause" command. The digital video recording apparatus 10 continues to buffer the broadcast events, as discussed below. The buffer 26 is "active" and continues to receive for recording the signals of the broadcast event. The use may change channels on the signal control box.

Fig. 4 illustrates a second schematic view in the first exemplary operation depicting the digital video recording apparatus 10 recording a second broadcast event in event buffer 2. The prior broadcast event 1 is designated a time-shift recorded buffer 28. The buffer 28 is "active" as being paused by the user. As discussed above, an "active" buffer is not subject to culling when recording a subsequent broadcast event. The digital video recording apparatus 10 records the signals of the broadcast event 2 in the time-shift event recording buffer 26.

Fig. 5 illustrates a third schematic view in the first exemplary operation depicting the digital video recording apparatus recording a third broadcast event. The prior broadcast event 2 is designated a time-shift event recorded buffer 28a; the time-shift event recorded buffer 28 is "paused" and thus "active" (not subject to culling). The digital video recording apparatus 10 records the signals of the broadcast event 3 in the time-shift event recording buffer 26.

Example 2

Figs. 6 and 7 illustrate schematic views of a second example of the recording buffer 26 and the recorded buffer 28 during operation of the digital video recording apparatus 10. The setup for Example 2 is the same as Example 1. With reference to Fig. 6, the user remains paused in the first recorded buffer 28 (event buffer 1) and the number of buffers is at N (in this example, N = 3). The live broadcast event being recorded in event recording buffer 26 (event buffer 3) is about to expire and a new event (future event) is about to broadcast.

In this example, event buffer 28 is "paused" and thus "active" and not selectable for culling. The digital video recording apparatus 10 then completes recording broadcast event 3 in recorded event buffer 28b (formerly recording event buffer 26). The buffer controller 22 allocates a new recording buffer 26 (not shown in Fig.6) and selects the oldest, non-active event recorded buffer 28 to delete or cull. The buffer controller 22 selects recorded event buffer 28a for culling, as shown in Fig. 6.

Fig. 7 illustrates a second schematic view in the second exemplary operation after the digital video recording apparatus culls recorded buffer 28a when recording a new broadcast event 4 in recording buffer 26.

Example 3:

Figs. 8 and9 illustrate schematic views of a third example of the recording buffer

26 and the recorded buffer 28 during operation of the digital video recording apparatus 10.

The setup for Example 3 is the same as Example 1 except the user has transitioned into the second recorded buffer 28a (which is "paused" and thus active). The number of buffers is at N.

With reference for this example to Fig. 8, the signals of broadcast event 1 are recorded in recorded event buffer 28; the digital video recording apparatus 10 recorded the signals during broadcast of event 2 in event buffer 28a and the user has "paused" buffer 28a; broadcast event 3 recorded in buffer 26 during recording is about to expire (and buffer 26 becomes buffer 28b); and a new future event about to broadcast. The buffer controller 22 selects the oldest, non-active buffer (event buffer 1) to cull, as depicted in Fig. 8.

Fig. 9 illustrates a second schematic view in the third exemplary operation after the digital video recording apparatus culls the buffer 28 (event buffer 1) when recording the new broadcast event 4 in the event recording buffer 26.

Example 4 - Over time of using the system

Fig. 10 illustrates a schematic view of a fourth example that depicts operation of the digital video recording apparatus 10 over time. Over time, the user's active presentation event will remain accessible. Any number (X) of events could have passed between the presentation event recorded in recorded buffer 28 and the then current live broadcast event being recorded in the live recording event buffer 26. The user may time- shift between any existing events (presentation event in recorded buffer 28, live event -1 recorded in recorded buffer 28a, and live event being recorded in recording event buffer 26). The user has the option to save any of the existing events in the active presentation. The former buffers designated with the "deleted event, unavailable" icon were previously culled during event recording operations discussed above and the content or signals are not available for play by the digital video recording apparatus 10 and viewing on the television 20.

Database 32

With reference to Fig. 1 , and as noted above, the user selectively saves a recorded buffer 28 as a saved buffer 30. The processor 14 is configured to allow the user to access selectively saved event buffers 30 for viewing.

Further, the broadcast events are coded with program information (date, time, title, descriptive summary of the event, parental controls, ratings, and the like). Such broadcast event information may be considered to be metadata. The processor 14 records in a database 32 the coded program information associated with each broadcast event recorded in a recording buffer 26 and also records the status of the event. The status of the event indicates whether the event is "saved" and thus not subject to culling (except as noted above), "paused", "active", or "live". The processor selectively presents the recorded database information on the television 20 to the user, as depicted generally 34 in Fig. 11. Using a controller, such as the control box control device, the user can scroll through the list of events 36, observe the broadcast date and time 38, the status of the event 40, event ratings 42 that conventionally indicate the nature of the event (parental advisory, violent, and the like rating indicators) and a description 44 of the event which may include details such as actors, event release date, and related information. The user then selects an event for presentation through the processor 14 and the signal output 18 for display on the television 20.

The foregoing describes various embodiments of the present invention that provides an apparatus and method to buffer live-broadcast events, which allows a subscriber to pause and rewind live broadcast television events for time-shift viewing. It is to be understood, however, that numerous changes and variations within the spirit and scope of the present invention may be made without departing therefrom.

The DVR can apply restrictions to the access of saved buffers. As previously explained, the date and time are recorded in relation to the saved buffers. The DVR can allow access to the saved buffer within a predefined timeframe. In an example, the access is allowed only during 24 hours. In case that the user requests the viewing of a saved buffer after that period, the access is denied. In addition or alternatively, the DVR can also automatically delete the content of one saved buffer when the authorization time is over. According to another embodiment, the recorded data are encrypted by a key pertaining to the digital video recording apparatus. This encryption prevents the possibility to disseminate the content of one buffer to third parties. The key to encrypt the buffer can be hidden within the software of the digital video recording apparatus. In case that a security module is attached to the digital video recording apparatus, the latter can request an encryption key to the security module. The security module then generates a temporary key Kt that will be used by the digital video recording apparatus. The security module then encrypts the temporary key Kt by a secret key Ks and send this cryptogram (Kt)Ks to the digital video recording apparatus. When the live buffer is full of encrypted data by the key Kt, this key is deleted from the DVR. Only the cryptogram is stored with the metadata associated with this buffer. For starting the recording of a new live event, a new temporary key Kt2 is requested by the DVR to the security module.

When a recorded buffer is requested by the user for viewing, the DVR reads from its memory the cryptogram (Kt)Ks and transmits it to the security module. In return the latter send the temporary key Kt to the DVR after decryption by its secret key Ks.

Instead of storing the cryptogram together with the metadata, a key identifier is stored.

- This key identifier could be generated by the DVR while requesting a temporary key Kt. The security module generates the temporary key and stores it in its memory together with the identifier. The generated temporary key is provided to the DVR.

At a later stage, when the buffer encrypted by the temporary key is requested for viewing, the DVR requests the security module to provide with the relevant temporary key. In the request, the DVR transmits the identifier to the security module, allowing the latter to retrieve the correct key. This key is then transmitted to the DVR.

- This key identifier can be generated by the security module when a temporary key is requested by the DVR. The security module returns to the DVR the temporary key and the identifier. These two elements are also stored in the security module. The step of accessing a saved buffer is the same as above.

The security module can enforce the restrictions to the access of the buffers. When a given temporary key is requested by the DVR, the security module can determine the time span between the generation of this key and the current request. The security module can refuse to return the expected temporary key if the conditions are not fulfilled (e.g. only 24 hours availability).

Security modules, as mentioned above, can be implemented in a variety of manners such as on a microprocessor card, on a smartcard or any electronic module in the form of a badge or key. These modules are generally portable and detachable from the receiver and are designed to be tamper-proof. The most commonly used form has electrical contacts but contactless versions of type ISO 14443 also exist. Another implementation of the security module exists where it is directly soldered inside the receiver, a variation of this being a circuit on a socket or connector such as a SIM module. Yet another implementation is to have the security module integrated on a chip which has another function e.g. on the de- scrambling module or on the microprocessor module of the decoder. The security module can also be implemented in software.

Claims

CLAIMS What is claimed is:

1 . A time- shift digital broadcast video recorder with a linear event buffer comprising a live broadcast event recording buffer and at least one broadcast event recorded buffer, each of the live broadcast event recording buffer and the broadcast event recorded buffer capable of filling to a predetermined size and logically connected together in sequence on a digital recording device, and a processor with a buffer controller configured to provide access to the linear event buffer for selective display of the broadcast event recorded in the live broadcast event recording buffer and the broadcast event recorded buffer.

2. The time-shift digital broadcast video recorder as recited in Claim 1, further comprising a signal input stage that communicates signals of a broadcast event to the processor.

3. The time-shift digital broadcast video recorder as recited in Claims 1 and 2, further comprising a signal output stage that communicates signals from the processor to an image display device.

4. The time-shift digital broadcast video recorder as recited in any of the Claims 1- 3, wherein the buffer controller is further configured to pause selectively one of said live broadcast event recording buffer and the broadcast event recorded buffer, which paused buffer is deemed to be active.

5. The time-shift digital broadcast video recorder as recited in Claim 4, wherein the buffer controller upon reaching a predetermined number of broadcast event recorded buffers, culls the oldest non-active broadcast event recorded buffer upon commencement of recording a new live broadcast event in a new event recording buffer.

6. The time-shift digital broadcast video recorder as recited in any of the Claims 1

- 5, wherein the processor is configured with capability for selective rewind, pause, stop and forward actions during display of the signals of the broadcast recording buffer or the broadcast event recorded buffer selectively.

7. The time-shift digital broadcast video recorder as recited in any of the Claims 1

- 6, wherein the buffer controller manages a live broadcast event recording buffer and two broadcast event recorded buffers.

8. The time-shift digital broadcast video recorder as recited in any of the Claims 1

- 7, wherein the buffer controller allocates buffer space for a broadcast event recroded buffer up to about 40% of an event recordable buffer space and reserves about 20%of the event recordable buffer space for commencing subsequent live broadcast event recording in a new event recording buffer.

9. The time-shift digital broadcast video recorder as recited in any of the Claims 1

- 8, wherein the processor records live broadcast event signals until a file time limit.

10. The time-shift digital broadcast video recorder as recited in Claim 9, wherein the file time limit is 6 hours.

11. The time-shift digital broadcast video recorder as recited in Claims 1 - 10, further comprising the processor configured for designating a selected broadcast recorded event buffer as a saved event buffer free from culling.

12. The time-shift digital broadcast video recorder as recited in Claiml 1 , wherein the buffer space of saved event recorded buffers is not counted against buffer size requirements.

13. The time-shift digital broadcast video recorder as recited in any of the Claims 1 - 12, further comprising a database of event metadata for the event recording buffer and the event recorded buffer.

14. The time-shift digital broadcast video recorder as recited in Claiml 3, further comprising the processor configured for selective display of event metadata recorded in the database for events that are saved, active and live, and a selection device by which a user selects one such event buffer for presentation of the signals on a display device.

15. The time-shift digital broadcast video recorder as recited in any of the Claims 1

- 14, further comprising means to encrypt the data recorded in the live broadcast event recording buffer and at the broadcast event recorded buffer and means to decrypt the encrypted data while reading one of the buffer.

16. The time-shift digital broadcast video recorder as recited in Claim 15, in which the encryption/decryption is carried out with at least one encryption key (Kt), this temporary key (Kt) being further encrypted by a secret key (Ks), the encrypted temporary key (Kt) being stored with the encrypted data of the buffer.

17. The time-shift digital broadcast video recorder as recited in Claim 15, wherein the recorder is connected with a security module, and the encryption/decryption is carried out with at least one encryption key (Kt), this temporary key (Kt) being stored into the security module.

18. A method of time-shifting digital broadcasts comprising the steps of:

(a) recording a live broadcast event in a live broadcast event recording buffer capable of filling to a predetermined size from a beginning point to an ending point of the live broadcast event after which the live broadcast event buffer becomes one of at least two broadcast event recorded buffers;

(b) commencing the recording of a new live broadcast event in a new live broadcast recording buffer;

(c) logically connecting the event recording buffer and the event recorded buffer; and

(d) selectively accessing the logically connected event recording buffer and the event recorded buffer for selective display of the broadcast event recorded therein.

18. The method of time-shifting digital broadcasts as recited in Claim 17, further comprising the steps of culling a selected one of the event recorded buffers; and providing capability to mark either the live broadcast event recording buffer or at least one of the broadcast event recorded buffers as paused, whereby the marked buffer is prevented from being culled.

19. The method of time-shifting digital broadcasts as recited in Claims 17 and 18, further comprising the steps of selecting the live broadcast event recording buffer or the event recorded buffer and communicating the signals recorded in the selected buffer to a display device.

20. The method of time-shifting digital broadcasts as recited in any of the Claims 17 - 19, further comprising the step of selectively rewinding, pausing, stopping, forwarding, or playing recorded signals from the live broadcast event recording buffer or the event recorded buffer selectively.

21. The method of time-shifting digital broadcasts as recited in any of the Claims 17 - 20, further comprising the step of a buffer controller allocating a live broadcasting buffer in a digital recording device upon commencement of a broadcasting event.

22. The method of time-shifting digital broadcasts as recited in any of the Claims 17 - 21, further comprising the step of saving the event recorded buffer to prevent the saved buffer from being culled.

23. The method of time-shifting digital broadcasts as recited in any of the Claims 17 - 22, further comprising the step of allocating a predetermined event buffer space on a digital memory device such that up to about 40% of a event buffer space is allocated to each of two event recorded buffers and about 20% of the event buffer space is allocated to the live broadcast event recording buffer, whereby the signals of the live broadcast event commence recording prior to culling of the selected event recorded buffer.

24. The method of time-shifting digital broadcasts as recited in any of the Claims 17 - 23, further comprising the steps of recording in a database metadata for each event recorded in the event recording buffer.

25. The method of time-shifting digital broadcasts as recited in Claim 24, further comprising the step of selectively displaying event metadata for buffered events and of presenting signals of a selected one of the buffered events.

26. The method of time- shifting digital broadcasts as recited in any of the Claims 17 - 25, further comprising the step of encrypting the data recorded in the live broadcast event recording buffer and at the broadcast event recorded buffer and a step of decrypting the encrypted data while reading one of the buffer.

27. The method of time-shifting digital broadcasts as recited in Claim 26, in which the encryption/decryption is carried out with at least one encryption key (Kt), this temporary key (Kt) being further encrypted by a secret key (Ks), the encrypted temporary key (Kt) being stored with the encrypted data of the buffer.

28. The method of time-shifting digital broadcasts as recited in Claim 26, wherein the recorder is connected with a security module, and the encryption/decryption is carried out with at least one temporary encryption key (Kt), this temporary key (Kt) being stored into the security module.