GB2354677A

GB2354677A - Copy protection of digital video broadcast data

Info

Publication number: GB2354677A
Application number: GB9922862A
Authority: GB
Inventors: Andrew Jim Kelley Glasspool; Mark Thomas Barrington
Original assignee: ON DIGITAL PLC
Current assignee: ON DIGITAL PLC
Priority date: 1999-09-27
Filing date: 1999-09-27
Publication date: 2001-03-28
Also published as: GB9922862D0; AU7435700A; EP1287695A1; WO2001024529A1

Abstract

A digital data stream broadcast according to DVB and MPEG-2 standards comprises packets containing data from elementary data streams and corresponding identification codes (PIDs). Packets containing identification information for indicating correspondence between the PIDs and elementary data streams are also formed. To prevent recording and later playback of the broadcast, false identification information is introduced into the packets. At a receiver the time and date information in the multiplexed broadcast data is checked and if it is not earlier than the receiver microprocessor's internal clock and calender then the false PID values are corrected to allow reconstruction of the elementary data stream. If the time and date is earlier then the PID values are not corrected and the recorded data will not be correctly reconstructed. Thus copy protected broadcast programmes cannot be recorded for later viewing but are available for immediate viewing and the need for an in clear signal between a controlled access module 204 and host apparatus 202 can be avoided.

Description

2354677 DIGITAL VIDEO BROADCASTING The present invention relates to

digital video broadcasting, in particular broadcasting compliant with the DVB standards as issued by ETSI which themselves cite the MPEG Video Standard: ISO/IEC 13818-2: Information technology - generic coding of moving pictures and associated audio information: Video (1996) (aka ITU-T Rec. H-262 (1996)) (hereinafter referred to as the MPEG-2 standard). The present invention also relates to broadcasting to a population of receivers compliant with the DVB standard EN50221:1997.

In current broadcasting systems it is known to provide arrangements for restricting access to certain programmes, for commercial or other reasons. A known method employs scrambling or encryption of the data content of one or more of the data streams of a programme for which access is to be restricted. In the case of the DVB; standard, an interface definition is included in the standard to enable provision of corresponding descrambling in a module known as a controlled access module, where this module is separate from a host apparatus.

Because of the digital nature of digital video broadcast it is relatively easy and cheap to make high 2 quality recordings of programme contents. Thus, in the case of broadcast of certain material, such as recently released movies, a commercial desire has arisen for a method of copy protection to be provided. The desire is for a form of copy protection under which access to a broadcast programme will be enabled for the purpose of immediate real time viewing, but at the same time copying, for example by a digital video recorder, will not be enabled.

A disadvantage with arrangements provided to date within the framework of the DVB standards is that following descrambling, an unscrambled signal, i.e. a signal 'in the clear', is passed from the controlled access module to the host apparatus.

The present invention advantageously provides a form of copy protection that is applicable to arrangements such as DVB. The form of copy protection provided can operate independently of the existing descrambling procedure provided for example by the DVB standards. The form of copy protection provided by the present invention can be employed to effectively avoid the existence of an in the clear signal between a controlled access module and a host apparatus without necessarily having to have a device within the host apparatus to enable reading of copy protected programmes.

3 In a first aspect the present invention provides a digital broadcast system which enables real time viewing but inhibits copying of the broadcasts by including misinformation in the broadcast.

In a second aspect the present invention provides apparatus for generating a digital data stream for transmission wherein information indicating the location in the data stream of a particular broadcast or a part of a broadcast (for example a video or audio data stream or portion thereof) is deliberately corrupted or falsified.

The present invention also provides a digital data stream generated by apparatus in accordance with the second aspect.

In a further aspect the present invention provides apparatus for extracting a broadcast from a digital data stream generated by apparatus in accordance with the second aspect despite the deliberate corruption or falsification of location information by using previously provided information or information provided with the digital data stream in, for example, an encrypted or scrambled form.

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings in which:

Figure I is a schematic illustration of a 4 broadcasting arrangement in accordance with the present invention; Figure 2 schematically illustrates the components of a broadcast system of an embodiment of the invention; Figure 3 illustrates functionally a broadcast processor of an embodiment of the invention; Figure 4 illustrates a portion of a multiplex stream of data employed in an embodiment of the invention; Figure 5 shows the processing operations performed by a broadcast processor in an embodiment of the invention; Figure 6A shows a multiplexed data stream provided in an embodiment of the invention; Figure 6B schematically illustrates PAT and PMT tables employed in an embodiment of the invention; Figure 7 shows the processing steps performed in the generation of PSI information tables in an embodiment of the invention; Figure 8 schematically illustrates functionally a receiver employed in an embodiment of the invention; Figure 9 shows the processing steps employed in the operation of a demultiplexer under the control of a microprocessor in an embodiment of the invention; and Figure 10 shows a schematic functional diagram illustrating one example of a receiver in combination with a video recorder employed in an embodiment of the invention; and Figure 11 shows a schematic functional block diagram illustrating another example of a receiver in combination with a video recorder.

Figure 1 schematically illustrates a broadcasting arrangement according to the present embodiment.

Broadcaster 2 broadcasts television programmes which in the present embodiment are received by receivers 4, 6 and 8 via transmission links 10, 12 and 14 respectively.

Broadcaster 2 broadcasts the television programmes in the format defined by the DVB, standards. Receivers 4, 6 and 8 are similarly compliant with the DVB standards including EN50221. 1997. Although only three receivers 4, 6, 8 are shown in Figure 1, in practice many more receivers will be arranged to receive broadcasts from broadcaster 2. Various forms of transmission link are employed by broadcaster 2 in the present embodiment. In the case of those shown in Figure 1, transmission link 10 represents terrestrial broadcast, transmission link 12 represents satellite broadcast and transmission link 14 represents cable broadcast.

Broadcaster 2 includes an arrangement, shown in Figure 2, for integrating and transmitting a plurality of television programmes in a single broadcast. Referring 6 to Figure 2, the arrangement includes a broadcast processor 20 whose input is coupled to programme store 22 storing pre-recorded programmes and programme feed 26 for supplying live programmes. Thus in the present embodiment a first television programme will be input into broadcast processor 20 from programme store 22, and a second television programme will be input into broadcast processor 20 from programme feed 26. In other examples a larger number of televisions programmes may be input. An output of broadcast processor 20 is coupled to transmitter 28. Transmitter 28 is arranged to transmit broadcasts via transmission links 10, 12 and 14.

Broadcast processor 20 will now be described in more detail with reference to Figure 3. The programmes are supplied from programme store 22 and programme feed 26 in the form of elementary data streams. In the present example, programme 1 as provided by programme store 22 is formed from two elementary data streams, that is one video stream 32 and one audio stream 33. Similarly, television programme 2 as provided by programme feed 26 consists of a single video stream 34, and two audio streams 33 and 35.

Broadcast processor 20 includes PID processor 30, where PID refers to Packet Identification Code as employed in the MPEG-2 standard which itself is employed 7 in the DVB standard. PID processor 30 is arranged to receive the elementary data streams 32 to 36 described above. PID processor 30 also includes a programme specific information (PSI) generator 38. PID processor 30 is coupled to packetiser 40 such as to forward the elementary data streams 32 to 36 and an output of PSI generator 38 to packetiser 40. Packetiser 40 is coupled to multiplexer 42. An output of multiplexer 42 forms an output of broadcast processor 20 and is thus coupled to transmitter 28 as described earlier.

To simplify the explanation of the operation of PID processor 30, it is first convenient to describe the form of the data packets that will be formed by packetiser 40 and thereafter multiplexed by multiplexer 42. Figure 4a shows a portion 50 of a multiplexed stream of such packets 52, 54 and 56. Packets 52, 54 and 56 comprise respective headers 58,62 and 66 and respective payloads 60, 64, 68, each of the format defined in the MPEG-2 standard. As further defined in the MPEG-2 standard, each header 58,62,66 is formed of the components shown in Figure 4b. of particular significance to the present embodiment is the part of the header shown as item 72 which carries the value of the PID. The PID serves to identify the elementary data stream from which the payload of the particular packet was derived. As defined 8 by the MPEG-2 standard, the PID consists of 13 bits, consequently its value can range from zero through to 8191.

Figure 5 shows the processing operations performed by broadcast processor 20 in this embodiment. At step S5, PID processor 30 identifies the source of each of the elementary data streams. At step S10, PID processor 30 allocates a respective PID value to each elementary data stream. At step S15, PSI information tables are generated, by PSI generator 38. In the present embodiment the PSI tables are of the form defined in the MPEG-2 standard. This consists of a hierarchy of look-up tables, by means of which a demultiplexer arrangement can ascertain which packets (in terms of PID-values) need to be extracted to obtain a particular TV programme. The hierarchy of tables begins with a Programme Association Table (PAT). The PAT associates each TV programme (e.g.

in the present case 'programme 1 1 and 'programme 21) with a corresponding PID value. Each such PID value serves as a pointer to a respective further table, namely a Programme Map Table (PMT). There is one PMT f or each television programme, and it itself contains a list of the elementary data streams constituting the television programme and a PID value for each said elementary data stream. Further details of step S15, in which the PSI 9 information tables are generated, will be given later below.

In the present example PID value 20 is allocated to the single video stream of programme 1, PID value 30 is allocated to the single audio stream of programme 1, PID value 40 is allocated to the single video stream of programme 2, PID value 50 is allocated to audio stream 1 of programme 2, and PID value 60 is allocated to audio stream 2 of programme 2.

At step S20 each data stream is packetized by packetizer 40, and similarly the PSI tables are packetized by packetizer 40. Each packet produced consists of a payload of 188 bits and a header containing the appropriate allocated PID value. At step S25 the packets are multiplexed into a single multiplexed data stream shown schematically in Figure 6A. Figure 6A shows by way of example one packet for each of the PID values employed in the present embodiment. Referring to Figure 6A, packet 80 contains content from the single video stream of programme 1 and has PID value 20, packet 82 contains content from the single audio stream of programme 1 and has PID value 30, packet 84 contains content from the video stream I of programme 2 and has PID value 40, packet 86 contains content from audio stream 1 of programme 2 and has PID value 50, packet 88 contains content f rom audio stream 2 of programme 2 and has PID value 60, packet 90 contains the PMT for programme 1 and has PID value 25, packet 92 contains the PMT for programme 2 and has PID value 77, and packet 94 contains the PAT and has PID value zero.

Step S15 in which the PSI generator generates the PSI information tables will now be described in more detail with reference to Figure 7. At step S35 the PAT is generated in a manner consistent with the MPEG-2 standard. In the present embodiment the correct PID values for each respective TV programme are inserted into the PAT, thus forming the PAT shown as item 100 in Figure 6B in which TV programme 1 is associated with PID value and programme 2 is associated with PID value 77. At step S40 a PMT is prepared for the first television programme to be considered, which in the present case is programme 1. Preparation of the PMT consists of listing each data stream that contains content of that television programme. Thus in the case of television programme 1, the list of data streams consists of a single video stream and a single audio stream. At step S45 the allocated PID values for these data streams are collected, i.e. PID value 20 for the video stream and PID value 30 for the audio stream. At step S50 the PSI generator determines whether the programme under consideration is to be copy protected. Such determination can be carried out dependent on a manual intervention by an operator, or can be based on criteria prestored in a memory of the PID processor 30. In the present example programme 1 is indeed to have copy protection applied thereto. Thus at step S55 the collected PID values, i.e. PID value of 20 for the video stream and PID value 30 for the audio stream, are adjusted. In the present embodiment each PID value is adjusted by having its value reduced by 1. Thus PID value 20 is adjusted to PID value 19, and PID value 30 is adjusted to PID value 29. At step S60, final PID values are determined as being equal to the adjusted PID values described immediately above. At step S70 the final PID values, in this case PID value 19 for the single video stream and PID value 29 for the single audio stream, are inserted into the PMT for programme 1, forming the complete PMT for programme 1 which is as shown as item 96 in Figure 6B. It can be seen by comparing Figure 6B with Figure 6A that the PID values for the data streams of programme I in PMT 96 are different from the PID values actually allocated to the packets carrying those data streams as payloads. At step S75 it is determined whether all of the programmes have been processed. In the present example programme 2 is still to be processed 12 so the process returns to S40 where the PMT is prepared f or programme 2. In this case the list of data streams consists of a single video stream plus audio stream 1 and audio stream 2. At step S45 the allocated PID values for these data streams are collected, i.e. PID value 40 for the video stream and PID values 50 and 60 for audio streams 1 and 2 respectively.

In the case of programme 2, at step S50 it is determined in the present embodiment that programme 2 is not required to have copy protection. Consequently the process moves to step S65 where the final PID values are set equal to the allocated PID values, in other words no adjustment of PID values takes place. Thus when at step S70 the final PID values are inserted from each stream to complete the PMT for programme 2, as shown by item 98 in Figure 6B, the PID values inserted are 40, 50 and 60 respectively, providing correct correspondence to the PID values allocated to the actual packets as shown in Figure 6A. Since programme 2 is the last programme to be considered in the present example, at step S75 the process continues on to step S20 as shown in Figure 5 and described earlier.

It will be appreciated that the above description is a simplified description of the process carried out to prepare the data streams for transmission because apart 13 from the adjusting of the PID values for copy protected programmes the process is as described in the DVB and MPEG-2 standards.

Receiver 4 will now be described in more detail with reference to Figure 8. Receiver 4 includes host apparatus 202, controlled or conditional access module 204 and display/loudspeaker apparatus 216. Host apparatus 202 and controlled access module 204 both comply with the DVB and MPEG-2 standards. The display/ loudspeaker apparatus 216 will generally be integrated with the host apparatus 202 to form a digital television set.

Host apparatus 202 includes tuner 206 coupled to demodulator 208 which itself is coupled to output 209.

Host apparatus 202 further includes input 210 coupled to demultiplexer 212 which itself is coupled to MPEG decoder 214. MPEG decoder 214 is coupled to an output which is connected to display/ loudspeaker apparatus 216. Host apparatus 202 further includes microprocessor 211 which is coupled to demultiplexer 212 and is also coupled to input/output 213.

Controlled access module 204 includes de-scrambler 218 which is coupled to input 220 and output 222.

Controlled access module 204 also includes microprocessor 224which is coupled to input/output 226 of controlled 14 access module 204. In the present arrangement output 209 of the host apparatus is connected to input 220 of the controlled access module, and output 222 of controlled access module 204 is connected to input 210 of host apparatus 202. These two connections form an interface which is defined in the DVB standards and termed the MPEG-2 transport stream interface. Input/output 213 of host apparatus 202 is coupled to input/output 226 of controlled access module 204. This latter connection forms a f urther logical interface which is def ined in the DVB standards and called the command interface.

In operation, an RF broadcast signal is received by tuner 206. Tuner 206 tunes to the appropriate RF frequency enabling it to forward the signal or channel, to demodulator 208. Demodulator 208 demodulates the broadcast multiplexed data stream from the RF carrier frequency. The frequency to which the tuner is tuned will depend upon the digital channel selected by the user.

The demodulated multiplexed packet stream is passed from output 209 of host apparatus 202 to input 220 of controlled access module 204 and then to descrambler 218.

In the present embodiment the programme contents within the respective video streams and audio streams have been scrambled in compliance with the DVB standards and in conventional fashion, for commercial reasons. It should be understood that this scrambling is separate to the additional copy protection selectively applied by adjusting PID-values in the present embodiment.

Descrambler 218 of controlled access module 204 descrambles the programme contents. The data stream output from descrambler 218 consists of the packets described above with reference to Figure 6A. This data stream is passed from output means 222 of controlled access module 204 via input means 210 of host apparatus 202 to demultiplexer 212 of host apparatus 202.

Demultiplexer 212, under control of microprocessor 211, demultiplexes the data stream using the PSI tables to extract a user-selected TV programme under instructions received from microprocessor 211.

In the present emboiment the demultiplexer 212 will be unable to extract the copy-protected programme 1 simply by using the PMT 96 for programme 1 because the PID values in the PMT 96 for programme 1 are f alse and do not correspond to the actual PID values for that programme. Upon receipt of an input signal at input 220, the microprocessor 224 checks the time and date information which is transmitted in the multiplexed data stream and, provided this time and date information is not earlier than that of the microprocessor's internal 16 clock and calendar, then the microprocessor 224 supplies signals across the command interface using a standard command, known as the tune command (which is defined in the DVB standards) to enable the microprocessor 221 to adjust the false PID values to the correct PID values.

The tune command can include such instructions for more than one initial PID value. This tune command can conventionally be employed for the purpose of controlled access module 204 arranging for an alternative visual or audio output to be provided to the user when that user is not authorised to have the content of the originally selected programme descrambled by descrambler 218. Thus the PID values to which microprocessor 211 redirects the multiplexer 212 will conventionally lead to the display of some type of message explaining that the requested programme cannot be viewed. However, this is in contrast to the present embodiment in which the tune command is employed to enable microprocessor 211 to redirect the multiplexer 212 back to the correct PID values of the requested television programme. In the present embodiment data identifying the PID values for such redirection is required, and the PID values to which the multiplexer 212 must be redirected are stored in the memory associated with microprocessor 224 until the required adjustment, being determined by the protocol 17 used by PSI generator 38 of PID processor 30 to generate PSI tables of the present embodiment.

Details of the operation of demultiplexer 212 under the control of microprocessor 211 will now be described with reference to Figure 9. At step S104 microprocessor 211 of host apparatus 202 receives a programme selection from a user of host apparatus 202. Any conventional user interface means, for example push button controls or infrared remote control, can be employed. At step S108 microprocessor 211 requests the contents of packets with PID value equal to zero from demultiplexer 212. These packets will contain the information forming PAT table 100.

At step S112 demultiplexer 212 supplies the corresponding packet contents to microprocessor 211 which therefore receives the information content of PAT table 100. At step S116, microprocessor 211 reads off the PID value. corresponding to the selected programme. If the programme selected is programme 1, then as can be seen from table 100 in Figure 6B, the PID value read off is PID value 25. At step S120, microprocessor 211 requests demultiplexer 212 to extract packets with PID value equal to 25 in the header. At step S124 demultiplexer 212 duly extracts the packets with PID value 25, that is the packets whose contents constitute the PMT for programme 18 1 (shown as item 96 in Fig. 6B) and supplies these packets to microprocessor 211. Microprocessor 211 now processes the PMT for programme 1 by re ading of f the PID values for the data streams that hold the content of programme 1. Thus as can be seen froM Figure 6B, in the present case microprocessor 211 reads off PID value 19 for the video stream and PID value 29 for the audio stream. At step S132 microprocessor 211 determines whether any of the read off PID values correspond to PID values for which retune commands have been received from microprocessor 224, as described earlier above. In the present case, because programme 1 is copy-protected the microprocessor 224 will have instructed the microprocessor 211 to adjust the PID values. In the present case the tune command would have instructed microprocessor 211 to adjust any PID values 19 to an adjusted value of 20 and any PID values of 29 to an adjusted value of 30. Accordingly, at step S136 the read off PID values of 19 and 29 are adjusted to 20 and 30, respectively. At step S140 microproce.ssor 211 sets a parameter called the "decided PID value", equal to the adjusted PID values of 20 and 30 in the present case. At step S148 microprocessor 211 instructs demultiplexer 212 to extract packets with the decided PID values that have been established as above, which in the present case are 19 PID value 20 and PID value 30. Thus, as can be seen with reference to Figure 6A, demultiplexer 212 has been instructed to extract packets whose PID values are the correct values for extracting the contents of programme 1, thus correctly enabling access to the copy protected programme. At step S156, MPEG decoder 214 decodes the extracted packets and at S160 the display/ loudspeaker apparatus 216 successfully presents the requested programme contents of programme 1.

In the present embodiment programme 2 is a programme which has not been copy protected according to the method of the present invention, in other words it is a programme that is allowed to be included in the clear, when passed from descrambler 218 of controlled access module 204 to demultiplexer 212 of host apparatus 202.

When progranune 2 is selected by a user, the process already described for programme 1 with reference to Figure 9 is similarly followed, except that at step S132 it is determined that none of the read of f PID values were included in the received tune commands.

Consequently the process moves to step S144 where the parameter called "decided PID value" is simply set equal to the actual read off PID values. Thereafter, by means of steps 148 onwards, programme 2 will be extracted from the multiplexed data stream and successfully presented by display/loudspeaker apparatus 216.

Figure 10 shows the receiver of Figure 8 coupled to a digital video recorder 242 to illustrate the effect of the copy-protection. Like parts to those shown in Figure 8 are given the same reference numerals. Digital video recorder 242 includes a microprocessor 252 coupled to an input/output 254, a recording means 260 and a playback means 270 coupled to an output 250.

Microprocessor 252 of the digital recorder 242 is coupled to the microprocessor 211 of the host apparatus 202 via input/output 254 of the digital video recorder 252 and a further input/output 230 of the host apparatus, this connection forming another example of the earlier described command interface compliant with the DVB standard. Output 250 of the digital video recorder 242 is connected to an additional input 240 of the host apparatus 202. Input 210 of the host apparatus is connected by switch SWl to the demultiplexer 212. Input 240 is also directly connected to the demultiplexer 212.

Switch SW1 is closed when the digital video recorder is not present but is otherwise open. An output 241 of the host apparatus 202 is connected to the record means 260 through input 251 of the digital video recorder.

The input 251 and output 250 of the digital video recorder 242 are coupled by a switch SW2 which is open 21 f or playback and closed during recording or when the digital video recorder 242 is idle.

Controlled access module 204 and host apparatus 202 function as previously described except that the output 222 of the controlled access module is coupled to the demultiplexer 212 via input 251, switch SW2 and output 250 of the digital video recorder 242 and input 240 of the host apparatus rather than directly through input 210 of the host apparatus. Thus, the copy protected television programme can be presented successfully for viewing directly in real time, that is at the time the programme is broadcast.

During a recording operation, the digital video recorder 242 records the whole multiplexed data stream.

on playback, the signal output by the playback means 270 is supplied directly to the demultiplexer 212 via the input 240. However, because the controlled access module 204 is not receiving an input signal at input 220, the microprocessor 226 does not supply instructions over the command interface to the microprocessor 221 to adjust any false PID values.

Thus, the demultiplexer 212 selects the false PID values and is not able to extract the required packets from the received multiplex data stream. Hence the demultiplexed signal supplied to the MPEG encoder 214 is 22 incorrect and the display/ loudspeaker apparatus 216 does not present the required programme despite the fact that this content was recorded by the digital video recorder 242. This means that the owner of the equipment shown in Figure 10 cannot record copy protected programmes for later viewing. This enables the broadcasters and suppliers of the broadcast to restrict or inhibit recording of certain programmes whilst still allowing immediate viewing of those programmes. This is of particular interest for, for example, the broadcast of recently released films or movies.

In the embodiment shown in Figure 10, the digital video recorder 242 records the entire multiplexed data stream. In another embodiment, the digital video recorder may be provided with its own demultiplexer and MPEG decoder to enable an operator of the video recorder to select a particular programme for recording (which may be different from a programme being presented in real time on the display/ loudspeaker apparatus 216). It will, however, be appreciated that because the digital video recorder 242does not receive any instructions from the microprocessor 226 of the controlled access module to adjust any false PID values, the digital video recorder will not be able to compensate for any false PID values and accordingly will not be able to copy any programme 23 carrying the copy protection described above.

Figure 11 shows a schematic functional block diagram similar to Figure 10 in which the positions of the digital video recorder 242 and controlled access module have been switched so that the microprocessor 252 of the digital video recorder is connected to the input/output 213, the record means 260 of the digital video recorder is connected to the output 209 of the host apparatus, the output 250 from the playback means 270 of the digital video recorder 242 is connected to the descrambler 218 of the controlled access module 204 via input 210 and output 241 of the host apparatus 202 and input 220 of the controlled access module 204. The descrambler 218 is connected via output 222 to the input 240 and then the demultiplexer 212 of the host apparatus.

With the arrangement shown in Figure 11, switch SW1 is closed when the controlled access module is not present but is otherwise open. Switch SW2 is open only during playback by the digital video recorder.

In this arrangement, the output of the demodulator 208 is recorded by the recorder 260 and upon playback the recorded signal is supplied from the playback means 270 to the descrambler 218 via output 250, input 210, output 241 and input 220. It would appear, at first glance, that the controlled access module 204 cannot tell whether 24 the signal received on input 220 comes directly from the demodulator 208 or is being received from the playback means 270 and that therefore it would not be possible for the controlled access module 204 to determine whether the signal being received is a real-time broadcast or a recorded signal. However, under the DVB standards, the multiplexed data stream includes time and date information in a TDTSI signal which is transmitted periodically in the multiplexed transport stream and may also include time and date information in the proprietary data stream. When the microprocessor 226 checks the time and date information in the signal received at the input 220 against its own clock and calendar, the time and date information in the signal will only match its own or be later than its own if the signal at the input 220 is a real-time broadcast signal received directly from the demodulator 208 via the closed switch SW2. If the signal received at the input 220 is a recorded signal from the playback means 270, then the time and date information in the received signal will relate to an earlier time and possibly also an earlier date. When the microprocessor 226 determines that the time and date information in the signal received at input 220 is earlier than its own time and date information, then the microprocessor 226 will not send instructions over the command interface to the microprocessor 211 to enable any false PID values to be adjusted. Accordingly, when the signal received at input 220 is a recorded signal, the demultiplexer 212 will not be able to extract the required packets from the received multiplexed recorded data stream and hence the signal supplied to the MPEG decoder 214 will be incorrect and the display/ loudspeaker apparatus 216 will not present the required programme.

Persons. authorised by the broadcaster to make copies may be provided with a digital video recorder in which microprocessor 252 is equipped with suitable compensation information, thereby enabling microprocessor 252 to initiate PID-value adjustment. This enables recording of the data streams of television programme 1.

In the above embodiment, programme 2 and any other programmes can be similarly copy protected if required.

Also, copy protection can be applied to other types of data streams in addition to video and audio, for example text data streams.

In the above embodiment the PID values as contained within a PMT were adjusted and effectively rendered false. In other embodiments one or more PID values within a PAT are varied instead of PID values in a PMT.

In other embodiments PID values from both one or more PMTs and the PAT are adjusted. Furthermore, whichever 26 type or types of table has its PID values altered, the number of PID values changed in each table may be one or more than one.

In the above described embodiments each PID value to be changed was changed in a systematic fashion consisting of reducing its value by one e.g. PID value 20 was changed to PID value 19. It is to be appreciated however that the present invention is not limited to this specific alteration. In other embodiments the PID value can be reduced by an amount greater than one, alternatively it can be increased by a specific value of one or more, or different PID values can be changed by different amounts. Furthermore any specific PID value can be varied by different amounts as a function of time.

one possibility is that the amount by which a PID value is changed is varied whenever a new television programme starts, or at advertisement breaks between programmes, and so on. Alternatively the amount by which PID values are to be changed can vary according to predetermined periods of time, e.g. every 30 minutes. Furthermore,' in other embodiments algorithms are employed to provide a more complicated function by which PID value variation amounts themselves vary over time or in response to certain events and inputs.

In other embodiments, any of the above ways of 27 adjusting PID values to provide copy protection can be applied intermittently, thus alternating with in the clear transmission. This would mean that access to a particular programme was only intermittently copy protected, however, that can sometimes be sufficient to fulfil the commercial or other reasons underlying the intention to copy protect a specific program.

In the above described embodiments, microprocessor 224 is pre-programmed with the algorithms or information necessary to achieve the required compensation. In other embodiments microprocessor 211 of host apparatus 202 can instead be preproqrammed with the required compensation information and algorithms to check that the time and date information in the multiplexed data stream is the same as or later than the time and date information from its own clock and calendar before adjusting any PID values. The preprogramming takes place in conjunction with preplanning of how the false PID values are to be included in the multiplexed packet streams. This tie-in will not always be ideal, and if details thereof needed to be changed, then the microprocessor will need to be amended. However, in other embodiments the required compensation information can be supplied after installation of microprocessors 224 and 211, and/or regularly updated, in various ways. one possibility is 28 that microprocessor 224 of controlled access module 204 has the relevant information input into it from a smart card. Such a smart card could therefore be provided on a conventional commercial basis. The smart card may also serve as a conventional smart card enabling descrambling on a commercial basis, or could be an additional smart card. Another possibility is that the correction instructions can themselves be supplied as part of the broadcasts received by host apparatus 202 and controlled access module 204. In this case microprocessor 224 would be preprogrammed to extract the relevant correction information from broadcasts. Such correction instructions could themselves be scrambled requiring descrambling by descrambler 218.

Although the above receiving and demultiplexing embodiments all relate to the DVB standards, the present invention can also be embodied in other digital TV arrangements and systems, and also in any other suitable communications systems, including ones other than television, for example radio, telephony and so on.

29

Claims

1. A -method of generating digital broadcast data for transmission, the method comprising:

forming packets of data each containing (i) data from a single elementary data stream, and (ii) an identification code corresponding to the respective single elementary data stream; generating identification information for indicating the correspondence between the identification codes and the elementary data streams; forming packets of data each containing (i) the generated identification information and (ii) an identification code corresponding to the identification information; and multiplexing the packets containing the data from the elementary data streams and the packets containing the identification information to form a multiplexed data stream; characterised in that the step of generating the identification information comprises providing a false indication of the correspondence of at least one identification code.

2. A method according to claim 1, wherein the identification codes are PID values, the identification information comprises a PAT and one or more PMTs, and the f alse indication is provided by adjusting at least one PID value in said PAT and/or one or more of said PMTs.

3. A method according to claim 1 or claim 2, further comprising generating correction information for transmission with the multiplexed data stream for enabling a receiver to adjust the at least one falsely indicated identification code.

4. A method according to any one of the preceding claims, further comprising transmitting the generated digital broadcast data.

5. A method of processing digital broadcast data, the method comprising:

receiving a multiplexed data stream comprising packets of data each containing (i) data from a single elementary data stream and (ii) an identification code corresponding to the respective single elementary data stream, the multiplexed data stream further comprising packets of data each containing (i) identification information indicating the correspondence between the 31 identification codes and the elementary data streams and (ii) an identification code corresponding to the identification information, wherein the identification -information comprises a false indication of the correspondence of at least one identification code; and employing correction instructions to adjust the at least one falsely indicated identification code in the identification information to enable packets from a selected elementary data stream to be extracted from the multiplexed data stream.

6. A method according to claim 5, wherein the identification codes are PID values, the identification information comprises a PAT and one or more PMTs, and the false. indication is provided by adjusting at least one PID value in said PAT and/or one or more of said PMTs.

7. Apparatus for generating digital broadcast data for transmission, the apparatus comprising:

means for forming packets of data each containing (i) data from a single elementary data stream, and (ii) an identification code corresponding to the respective single elementary data stream; means for generating identification information for indicating the correspondence between the identification 32 codes and the elementary data streams; means for forming packets of data each containing (i) the generated identification information and (ii) an identification code corresponding to the identification information; and means for multiplexing the packets containing the data from the elementary data streams and the packets containing the identification information to form a multiplexed data stream, characterised in that the means for generating the identification information comprises means for providing a false indication of the correspondence of at least one identification code.

8. Apparatus according to claim 7, wherein the identification codes are PID values, the identification information comprises a PAT and one or more PMTs, and the false indication is provided by adjusting at least one PID value in said PAT and/or one or more of said PMTs.

9. Apparatus according to claim 7 -or 8, further comprising means for generating correction information for use by a receiver in adjusting the at least one falsely indicated identification code.

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10. Apparatus according to claim 7, 8 or 9, further comprising means for transmitting the generated digital broadcast data.

11. Apparatus for processing digital broadcast data, the apparatus comprising:

means for receiving a multiplexed data stream comprising packets of data each containing (i) data from a single elementary data stream and (ii) an identification code corresponding to the respective single elementary data stream, the multiplexed data stream further comprising packets of data each containing (i) identification information indicating the correspondence between the identification codes and the elementary data streams and (ii) an identification code corresponding to the identification information, wherein the identification information comprises a false indication of the correspondence of at least one identification code; and means for employing correction instructions to adjust the at least one falsely indicated identification code in the identification information to enable packets from a selected elementary data stream to be extracted from the multiplexed data stream.

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12. Apparatus according to claim 11, wherein the identification codes are PID values, the identification information comprises a PAT and one or more PMTs, and the false indication is provided by adjusting at least one PID value in said PAT and/or one or more of said PMTs.

13. A digital data broadcasting system, comprising apparatus according to any one of claims 7 to 9, means for modulating a transmission carrier signal with the generated digital broadcast data; means for demodulating a received transmission carrier signal to retrieve the digital broadcast data; and apparatus according to claim 11 or claim 12.

14. A controlled access module arranged to use a tune command facility to communicate correction instructions related to falsely indicated identification codes to a host apparatus.

15. A digital television for receiving digital broadcast data comprising a multiplexed packet data stream, the television comprising:

a demultiplexer for extracting packets representing a selected elementary data stream, and demultiplexer control means adapted to control the demultiplexer to extract packets representing the selected elementary data stream using a correct identification code value rather than a false identification code supplied in the digital broadcast data.

16. A digital video recorder arranged to correct falsely indicated identification codes.

17. A digital video recorder for recording digital broadcast data comprising a multiplexed packet data stream, the digital video recorder comprising:

18. A method of inhibiting copying of a digital broadcast which comprises generating the digital data to be broadcast using a method in accordance with claim 1.

19. A signal comprising data from a plurality of elementary data streams arranged in a multiplexed data 36 stream; the multiplexed data stream comprising:

packets of data each containing (i) data from a single elementary data stream, and (ii) an identification code corresponding to the respective single elementary data stream; and packets of data each containing (i) identification information and (ii) an identification code corresponding to the identification information, where the identification information is for indicating the correspondence between the identification codes and the elementary data streams; characterised in that the identification information comprises a false indication of the correspondence of at least one identification code.

20. Apparatus for processing data for transmission to a receiver arranged to identify data on the basis of an identification code transmitted with the data, which apparatus comprises means for allocating an incorrect or false identification code to the data.

21. Apparatus for processing data transmitted after processing using an apparatus in accordance with claim 20, which apparatus comprises:

means for retrieving transmitted data using an 37 adjusted identification code rather than the incorrect or false identification code transmitted with the data.

22. A method of generating digital broadcasting data substantially as hereinbefore described.

23. A method of processing digital broadcast data substantially as hereinbefore described.

24. Apparatus for generating digital broadcast data substantially as hereinbef ore described with reference to the accompanying drawings.

25. Apparatus for processing digital broadcast data 15 substantially as hereinbef ore described with reference to the accompanying drawings.

26. A controlled access module substantially as hereinbef ore described with reference to the accompanying 20 drawings.