GB2405988A

GB2405988A - Audio/Video player providing restorable, impaired A/V material

Info

Publication number: GB2405988A
Application number: GB0321359A
Authority: GB
Inventors: Martin John Brennan
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-09-12
Filing date: 2003-09-12
Publication date: 2005-03-16
Also published as: GB0321359D0

Abstract

An audio/video material player (78) is provided, comprising a memory device (12), a data processor (80) and data input means (82), the memory device (12) having a read-only portion (120) and a read/write portion (122), the read-only portion having stored in it identification data and the read/write portion having stored in it an impaired version of audio/video material into which a reversible impairment has been introduced using impairment introduction data derived from the identification data and from authorisation data, the player (78) being operable, in the absence of authorisation data, to play the impaired version of the audio/video material, and the data processor (80) being operable to receive authorisation data from the data input means (82), to derive impairment removal data from the identification data and the authorisation data, and to use the impairment removal data to reverse the reversible impairment of the audio/video material to enable the player (78) to play a restored version of the audio/video material.

Description

Title: Audio/Video Material Plaver

Field of the Invention

This invention relates to an audio/video material player, to a method of making such a player, to a method of introducing a reversible impairment into audio/video material, to a method of reversing a reversible impairment of audio/video material to obtain a restored version of the material, to a computer program executable to introduce a reversible impairment into audio/video material, and to a computer program operable to reverse a reversible impairment of audio/video material to obtain a restored version of the material.

Background to the Invention

Audio/video material players are now available that do not use removable data storage media to store audio/video material, but instead use memory devices that are typically contained in the players and, in normal use, are not removable from the players.

One such player is sold under the name "TIVO" and incorporates a hard disk drive to store broadcast audio/video material for subsequent playback.

The inventor has appreciated that such audio/video material players are at present sold with no, or next to no, audio/video material stored in their memory devices, and that players with audio/video material stored in their memory devices would be attractive to potential purchasers of such players.

The inventor has further appreciated that it would be attractive to distributors of audio/video material to have an impaired version of their audio/video material stored in the memory devices of such players, so as to enable users of the players to play the impaired version of the material before deciding whether to buy a restored version of the material.

Summary of the Invention

According to a first aspect of the invention there is provided an audio/video material player that has a memory device, a data processor and data input means, the memory device having a read-only portion and a read/write portion, the read-only portion having stored in it identification data and the read/write portion having stored in it an impaired version of audio/video material into which a reversible impairment has been introduced using impairment introduction data derived from the identification data and from authorisation data, the player being operable, in the absence of authorisation data, to play the impaired version of the audio/video material, and the data processor being operable to receive authorisation data from the data input means, to derive impairment removal data from the identification data and the authorisation data, and to use the impairment removal data to reverse the reversible impairment of the audio/video material to enable the player to play a restored version of the audio/video material.

The invention therefore provides an audio/video material player that enables a user of the player to play an impaired version of audio/video material before deciding whether to buy a restored version of the material, that enables a distributor of audio/video material to provide the user of the player with the restored version of the material simply by providing him with authorization data, and that can make obtaining the restored version of the material from a copy of the impaired material so difficult as to be impractical.

It is to be appreciated that the expression "audio/video material player" is not intended to limit the invention to equipment that is operable only to play audio/video material, but is intended to encompass, for example, equipment that is operable both to record and to play audio/video material.

"Audio/video material" means digital signals representing audio and/or video material.

Audio material includes, for example, music, spoken words and other sounds. Video material includes still and moving images, such as photographic images, television programmes and films.

The data processor may advantageously be operable to store the authorisation data in the read/write portion of the memory device.

In that case, each time the player plays the restored version of the audio/video material, the data processor reads the authorisation data from the read/write portion of the memory device and the identification data from the read-only portion of the memory device, derives the impairment removal data from the identification and authorisation data and uses the impairment removal data to reverse the reversible impairment of the impaired version of the audio/video material stored in the read/write portion of the memory device.

This arrangement is advantageous because the restored version of the audio/video material is not stored in the memory device, and a person who copies the contents of the memory device to another memory device obtains only a copy of the impaired version of the material.

Preferably the identification data stored in the read-only portion of the memory device are substantially unique to the memory device.

In that case, a user who copies the contents of the memory device to another memory device cannot easily obtain the restored version of the audio/video material even using a player in accordance with the first aspect of the invention, because the other memory device will have different identification data stored in its read-only portion, and the data processor of the player will therefore derive different impairment removal data from those required to obtain the restored version of the material. In order to obtain the restored version of the material the user would need either to modify the operation of the data processor of the player, or use a computer to emulate such modified operation of the data processor. Such modification of the operation of the data processor of the player, or use of a computer to emulate such modified operation of the data processor would be far beyond the ability of most users. /

The player preferably includes algorithm execution means operable in accordance with a randomly generated algorithm to derive the impairment removal data from the identification data and authorisation data.

Preferably the algorithm execution means comprises a programmable logic device (PLD) that is programmed with the randomly generated algorithm during manufacture of the player.

In that case, it is even more difficult for a person who copies the contents of the memory device to another memory device to obtain the restored version of the material, because he must also determine the algorithm with which the PLD of the player is programmed.

Some PLDs have a security bit that can be set when the PLD is programmed and prevents a program with which the PLD has been programmed from being read from the PLD.

Where the security bit of the PLD has been set, the program with which the PLD has been programmed can be determined only by inspecting the structure of the PLD with an electron microscope, which for the vast majority of people would be impractical.

The memory device may be any means for storing digital signals, for example a compact disc rewritable (CD-RW) or digital versatile disc rewritable (DVD-RW), together with a suitable disc reader/writer.

Preferably, however, the memory device is a hard disk drive or electrically erasable programmable read-only memory (EEPROM).

The data input means may be, for example, an alphanumeric keypad, optical character recognition means, a bar code reader, or a magnetic or smart card reader.

The authorisation data could accordingly be provided to the user in the form of a printed document, or magnetic or smart card. The user would either read the authorisation data from the printed document and type the authorisation data into the device himself, or the s device would itself read the optical characters or bar code representative of the authorisation data from the printed document, or the device would read the authorisation data from the magnetic or smart card.

Preferably, however, the data input means comprises interface means operable to connect the device to a telecommunications network, typically the Internet. The authorisation data would then be provided to the device from an authorisation data server across the telecommunications network.

It is envisaged that a user of a device in accordance with the first aspect of the invention would play the impaired version of the material, be provided with authorisation data in return for payment, and preserve those portions of the audio/video material of interest to him, and overwrite the remaining portions of the material with his own audio/video material.

In this connection, the audio/video material preferably comprises a plurality of audio/video material tracks, into each of which tracks a respective reversible impairment has been introduced using impairment introduction data derived from the identification data of the memory device and authorisation data specific to that track.

A track, in the case of audio material, may correspond, for example, to an individual song or piece of music, an album, or an episode of a radio programme. In the case of video material, a track may correspond, for example, to an individual image, a film, or an episode of a television programme.

This simplifies the tasks of preserving portions of the audio/video material of interest to the user, and overwriting the remaining portions of the material with his own audio/video material, because the user can preserve those tracks of interest to him and overwrite the remaining tracks. An\

Moreover, the user need purchase only the authorisation data corresponding to those tracks of interest to him.

The invention is of particular advantage to distributors of back catalogue audio/video material, because people are, in general, loth to discard anything of value. By back catalogue audio/video material is meant material that, for example, is outmoded, and therefore cannot profitably be distributed through conventional distribution outlets, such as record shops. Users of players in accordance with the invention are therefore likely to play at least some of each impaired material track before overwriting the track, just in case the material is of interest. In this way the distributor of the back catalogue material is provided with a large audience of potential buyers of his back catalogue material, who would otherwise be unaware of the material.

The player may advantageously be operable to overwrite with the user's own material those impaired material tracks stored in the memory device of the player for which the user has not purchased the authorisation data in preference to writing the user's own material to blank portions of the memory device.

In the preferred embodiment of the invention, the impairment removal data used to reverse the reversible impairment of the audio/video material are identical with the impairment introduction data used to introduce the reversible impairment into the material.

According to a second aspect of the invention there is provided a method of producing an audio/video material player in accordance with the first aspect of the invention, the method comprising the steps of reading identification data from a read-only portion of a memory device, generating authorisation data, deriving impairment introduction data from the identification data and authorisation data, using the impairment introduction data to introduce a reversible impairment into audio/video material to produce an impaired version of the material, and writing the impaired version of the audio/video material to a read/write portion of the memory device.

Preferably the method farther comprises the steps of generating random algorithm data, writing the algorithm data to algorithm execution means operable to execute an algorithm determined by the algorithm data, and using the algorithm determined by the algorithm data to derive the impairment introduction data from the identification and authorisation data.

According to a third aspect of the invention there is provided a method of introducing a reversible impairment into audio/video material, the method comprising the steps of carrying out a lossy compression process on the audio/video material to produce lossy compressed audio/video material, introducing a reversible impairment into the lossy compressed audio/video material to produce impaired lossy compressed audio/video material, and carrying out a lossless compression process on the impaired lossy compressed audio/video material.

Preferably the lossy compression process comprises the lossy stages of MPEG Audio Layer 3 encoding of digital audio material, which produce an array of 576 quantised coefficients representative of 576 frequency components of the digital audio material, the introduction of the reversible impairment into the lossy compressed audio/video material comprises carrying out a reversible logical operation on at least a portion of one or more of the 576 quantised coefficients, and the lossless compression process comprises the lossless stages of MPEG Audio Layer 3 encoding of the 576 quantised coefficients into which the reversible impairment has been introduced.

In a preferred embodiment of the invention the reversible logical operation is an exclusive OR operation, which is carried out on the three least significant bits of the second sixteen of the 576 quantised coefficients.

The 576 quantised coefficients correspond to 36 frequency bands, each of which is divided into sixteen sub-bands. The first sixteen of the 576 quantised coefficients correspond to the sixteen sub-bands of the lowest frequency band. The second sixteen of the 576 quantised coefficients correspond to the sixteen sub-bands of the second lowest frequency band. It has been found that carrying out the exclusive OR operation on the three least significant bits of the second sixteen of the 576 quantised coefficients gives rise to a low frequency rumbling noise that is irritating to a listener but does not significantly obscure the audio material.

According to a fourth aspect of the invention there is provided a method of reversing a reversible impairment of audio/video material stored in a memory device of an audio/video material player in accordance with the first aspect of the invention to obtain a restored version of the material, the method comprising the steps of reading identification data from a read-only portion of a memory device of an audio/video material player, deriving impairment removal data from the identification data and from authorization data, and using the impairment removal data to reverse a reversible impairment of audio/video material stored in a read/write portion of the memory device.

Preferably the method further comprises the step of using algorithm execution means that has been programmed with a randomly generated algorithm to derive the impairment removal data from the identification data and the authorization data.

According to a fifth aspect of the invention there is provided a computer program executable by data processing means to perform a method in accordance with the third aspect of the invention.

According to a sixth aspect of the invention there is provided a computer program executable by a data processor of an audio/video material player in accordance with the first aspect of the invention to perform a method in accordance with the fourth aspect of the invention.

Brief Description of the Drawing Figures

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of apparatus for producing an audio player in accordance with the first aspect of the invention; Figure 2 is a block diagram of a portion of a database for use in production of such an audio player; Figure 3 is a schematic diagram of the operation of a programmable logic device that forms part of such a player; Figure 4 is a schematic diagram of the operation of a microprocessor of the apparatus of Figure 1 when introducing a reversible impairment into a 16-bit audio data word; and Figure 5 is a block diagram of an audio player in accordance with the first aspect of the invention.

Detailed Description of an Embodiment

The apparatus of Figure 1 comprises a computer 10, an external hard disk drive 12 and a programmable logic device (PLD) programmer 14. The computer 10 includes a microprocessor 16, an internal hard disk drive 18 and a data input/output interface 20.

The interface 20 enables data to be transferred between the microprocessor 16 and the external hard disk drive 12 and the PLD programmer 14. A PLD 22 is connected to the PLD programmer 14.

The hard disk of the external hard disk drive 12 is divided by control logic, which is not shown in Figure 1, into a read-only portion 120 and a read/write portion 122. The read- only portion 120 of the hard disk has stored on it a model number and a unique 64-bit serial number.

The internal hard disk drive 18 of the computer has stored in it unencoded mono digital audio tracks and a program executable by the microprocessor 16. For the purpose of clarity, the following description relates to production of a mono audio player, but it will be appreciated that the process could easily be adapted to production of a stereo audio player or a video player. No

The internal hard disk drive 18 also has stored in it a database, a portion of which is shown in Figure 2. Turning to Figure 2, the database 24 is divided into one thousand data blocks, each such data block corresponding to an external hard disk drive that will be used to produce an audio player. Three such data blocks are shown in Figure 2, denoted by reference numerals 26, 28 and 30. Each data block consists of a model number field 32, a 64-bit serial number field 34, a 32-bit identification data word field 36, a 32-bit algorithm data word field 38, one thousand track number fields and one thousand 32-bit authorization data fields. Only the first two track number fields, denoted by reference numerals 40 and 42, the first two 32-bit authorization data word fields, denoted by reference numerals 44 and 46, the last two track number fields, denoted by reference numerals 48 and 50, and the last two 32-bit authorization data word fields, denoted by reference numerals 52 and 54, are shown in Figure 2.

The database 24 is so structured that, for each data block, the first track number field 40 is related to the first 32-bit authorization data word field 44, the second track number field 42 is related to the second 32-bit authorization data word field 46, and so on. The database 24 can be interrogated by entering the model number and 64-bit serial number of a hard disk drive, so as to identify a particular data block in the database, and by entering a track number so as to identify the 32-bit authorization data word within the data block related to the track number. At the beginning of the process for producing the audio player the fields of the database all have zero data values stored in them.

The program stored in the hard disk drive 18 of the computer is executable by the microprocessor 16 to cause the operations described below to be carried out.

1. An "identify drive" command is transmitted to the external hard disk drive 12 by the interface 20, which causes the external hard disk drive to transmit the model number and 64-bit serial number stored on the readonly portion 120 of its hard disk to the microprocessor 16. The ATA interface as defined in ANSI NCITS 317-1998 AT Attachment-4 with Packet Interface Extension includes an "identify drive" command for this purpose.

2. A 32-bit identification data word is generated from the 64-bit serial number of the hard disk drive 20 by concatenating the four least significant bits of each byte of the serial number. The model number is written to the model number field 32a of the datablock 26 of the database 24 and the 64-bit serial number and 32-bit identification data word are written, respectively, to the 64-bit serial number field 34a and 32-bit identification

data word field 36a.

3. A random 32-bit algorithm data word is generated and written to the 32bit algorithm

data word field 38a of the datablock 26.

4. A text hardware description language file is generated from the 32-bit algorithm data word and describes a logic device operable to generate a 32-bit impairment introduction data word from the 32-bit algorithm data word, the 32-bit identification data word and a 32-bit authorisation data word. The operation of the logic device described by the text hardware description language file is described in greater detail below with reference to Figure 3.

5. A programmable logic device (PLD) design is compiled from the text hardware description language file and transmitted to the PLD programmer 14 by the interface 20. The PLD programmer programs the PLD 22 with the PLD design and also programs a security bit of the PLD 22 such that the PLD design with which the PLD 24 has been programmed cannot be read from the PLD.

6. A track number is generated and written to the track number field 40a of the datablock 26 of the database 24.

7. A random 32-bit authorisation data word is generated and written to the authorisation

data word field 44a of the datablock 26.

8. A 32-bit impairment introduction data word is generated from the 32bit algorithm data word, the 32-bit identification data word and the 32bit authorisation data word.

9. The impairment introduction data word is used to seed a 32-bit pseudorandom number generator. The pseudo-random number generator is a 32-bit linear feedback shift register that implements the polynomial X32 + X7 + X5 + X3 + X2 + X + 1.

10. A sequence of sixteen 32-bit pseudo-random numbers is generated by the pseudo- random number generator.

11.An initial set of 576 samples of an unencoded digital audio track is read from the internal hard drive 18. The 576 samples are filtered by a polyphase filterbank then by a modified discrete cosine transform filterbank and are analysed using a perceptual model then quantised to give a set of 576 quantised coefficients. This process is the lossy stage of MPEG Audio Layer 3 encoding and is described in greater detail in Annexe C of international standard ISO 11172-3 1993, in which the 576 quantised coefficients are referred to in section C.1.5.4.4.1 as ix(n).

12. The second sixteen quantised coefficients are separated into sign and magnitude components, which for the sake of consistency with the description of operation 11, will be referred to as sx(n) and mx(n) respectively. An exclusive OR operation is carried out on the three least significant bits of each of the set of sixteen 32-bit pseudo- random numbers and the three least significant bits of the sixteen magnitude components mx(n) of the second sixteen of the 576 quantised coefficients ix(n). The resulting sixteen impaired magnitude components, which will be referred to as imx(n) are recombined with their respective sign components sx(n) to give sixteen impaired quantised coefficients and 560 unimpaired coefficients, which will be referred to in the following description as iix(n). The exclusive OR operation carried out on the set of sixteen 32-bit pseudo-random numbers and the magnitude components of the second sixteen of the 576 quantised coefficients is described below in greater detail with reference to Figure 4.

13. Bit counting of fix(n) is carried out as described in sections C.1.5. 4.4.2 to C.1.5.4.4.8 and Huffman encoding and framing of fix(n) are carried out as described in section C.1.5.3.7 of Annexe C of international standard ISO 11172-3 1993 to generate an encoded frame. The calculation of the distortion described in section C.1.5.4.3.3 is carried out on ix(n) rather than iix(n).

14. Operations 11 to 13 above are iterative and may be carried out several times on the set of 576 samples before an encoded frame of the required length is generated. The exclusive OR operation 11 is carried out each time, but the same sequence of sixteen pseudo-random numbers from the pseudo-random number generator is used each time until the encoded frame of the required length is generated. The encoded frame is written to the read/write portion 122 of the hard disk of the external hard disk drive 12.

15. Operations 9 to 14 are repeated with subsequent sequences of sixteen 32-bit pseudo- random numbers from the pseudo-random number generator and subsequent sets of 576 samples of the unencoded digital audio track until the entire unencoded digital audio track has been encoded and written to the external hard disk drive 12.

16. Operations 6 to 15 are repeated with subsequent track numbers, subsequent random authorisation data words and subsequent impairment introduction data words, until one thousand digital audio Racks have been encoded and written to the external hard disk drive 12.

17. A look-up table 124 is written to the external hard disk drive 12. The look-up table 124 has a track number field for each encoded audio track that has been written to the external hard disk drive and an authorisation data word field related to each track number field. The track number of each encoded audio track that has been written to the external hard disk drive is written to a respective track number field of the look-up table. Zero data values are written to the related authorisation data word fields of the look-up table. A program executable by a microprocessor of a player is also written to the external hard disk drive 12.

18. The external hard disk drive 12 and the programmed PLD are installed in an audio player, which is described below with reference to Figure 5.

Turning to Figure 3, the logic device described by the text hardware description language file is shown schematically and denoted by reference numeral 56. The operation of the logic device is identical with that of the PLD 22 of Figure 1 after the PLD 22 has been programmed with the PLD design by the PLD programmer 14. The logic device 56 has stored in it a 32-bit algorithm data word 58 and is operable to receive a 32-bit identification data word 60 and a 32-bit authorization data word 62 and to generate a 32-bit impairment introduction data word 64. For each bit of the algorithm data word 58 the logic device determines whether the bit (bit n, say) is set (one) or reset (zero). If bit n of the algorithm data word 58 is set, the corresponding bit of the impairment introduction data word 64 is made equal to bit n of the authorization data word 62. If bit n of the algorithm data word 58 is reset, bit n of the impairment introduction data word 64 is made equal to bit n of the identification data word 60. For the purpose of clarity, only the first and last portions of the algorithm, identification, authorization, and impairment introduction data words 58, 60, 62 and 64, respectively, are shown in Figure 3.

Turning next to Figure 4, this shows the operation of the microprocessor of the computer shown in Figure 1 when carrying out the exclusive OR operation on a 16-bit magnitude component of a quantised coefficient and a 32-bit pseudo-random number to generate an impaired 16-bit magnitude component. The microprocessor implements three exclusive OR gates 66, 68 and 70, is operable to receive a 16-bit magnitude component 72 and a 32bit pseudo-random number 74 and to generate an impaired 16-bit magnitude component 76. For the purpose of clarity, only the three most significant bits 74a and the four least significant bits 74b of the pseudo-random number 74 are shown in Figure 4.

The thirteen most significant bits 72a of the magnitude component 72 are unchanged by the exclusive OR operation and the thirteen most significant bits 76a of the impaired magnitude component are therefore identical with the thirteen most significant bits 72a of the magnitude component 72. The three least significant bits 72b of the magnitude component 72 and the three least significant bits 74b of the pseudo-random number 74 are each transmitted to a respective exclusive OR gate. The most significant bits (1 and 1) of the three are transmitted to exclusive OR gate 66, the nextmost significant bits (1 and 1) of the three are transmitted to exclusive OR gate 68 and the least significant bits (1 and 0) of the three are transmitted to exclusive OR gate 70. The resulting bits generated by gates 66, 68 and 70 form the most significant (0), next most significant (0) and least significant (1) bits, respectively, of the three least significant bits 76b of the impaired magnitude component 76.

The 576 quantised coefficients produced by the lossy stage of MPEG Audio Layer 3 encoding are made up 36 frequency bands, each of which is made up of sixteen sub-bands.

The first sixteen quantised coefficients are therefore the sixteen subbands of the first, and lowest, frequency band. It has been found that impairing the second sixteen quantised coefficients gives rise to a low frequency rumbling noise that is irritating to the listener but does not significantly obscure the audio material.

The blocks of 576 quantised coefficients generated by the MPEG Audio Layer 3 encoding process are, in general, "long blocks" and the impairment process described above is carried out on such long blocks. However, occasionally transients in the unencoded audio material mean that a block of 576 quantised coefficients generated by the MPEG Audio Layer 3 encoding process is in fact three "short blocks". Where a block of 576 quantised coefficients is made up of three short blocks, the exclusive OR operation is not carried out on the second sixteen of the 576 coefficients and, although the sequence of sixteen pseudo- random numbers is generated, they are simply discarded, and 576 unimpaired coefficients are Huffman encoded and written to the hard disk drive 12.

Turning to Figure 5, an audio player 78 comprises a microprocessor 80, the hard disk drive 12 and PLD 22 shown in Figure 1, and a data input/output interface 82. A user keypad 84 enables a user of the player to enter track numbers of tracks to be played and authorisation data into the player. The hard disk drive 12 has stored in it a program executable by the microprocessor to cause the operations described below to be carried out.

1. A track number entered into the player by the user is matched with a track number stored in a track number field of the look-up table 124 stored in the hard disk drive 12 of the player. The 32-bit authorization data word stored in the authorization data word field related to the track number field is read from the look-up table and transmitted to the PLD 22.

2. The model number and 64-bit serial number of the hard disk drive 12 are read from the read-only portion of the hard disk of the hard disk drive 12. A 32-bit identification data word is generated as described above by concatenating the four least significant bits of each byte of the 64-bit serial number. The 32-bit identification data word is transmitted to the PLD 22.

3. The PLD 22 generates a 32-bit impairment removal data word from the 32bit identification data word and the 32-bit authorization data word. The operation of the PLD is as described above in relation to Figure 3.

4. The 32-bit impairment removal data word is used to seed a 32-bit pseudo-random number generator, which is a 32-bit linear feedback shift register that implements the polynomial X32 + X7 + X5 + X3 + X2 + X + 1 S. A sequence of sixteen 32-bit pseudo-random numbers is generated by the pseudo- random number generator.

6. An initial encoded frame of the audio track identified by the track number is read from the hard disk drive 12 of the player and the lossless compression stage of the MPEG Audio Layer 3 encoding is reversed to give a set of sixteen impaired quantised coefficients and 560 unimpaired quantised coefficients.

7. The sixteen impaired quantised coefficients are separated into sign and magnitude components sx(n) and mx(n). The exclusive OR operation described above is carried out on the three least significant bits of each of the set of sixteen 32-bit pseudo-random numbers and the three least significant bits of the set of sixteen magnitude components mx(n) of the impaired quantised coefficients. The set of sixteen impaired coefficients are, as explained above, the second sixteen of the 576 quantised coefficients. The magnitude and sign components are recombined to give sixteen unimpaired coefficients. Where an encoded frame of 576 quantised coefficients is made up of three short blocks, rather than a single long block, the exclusive OR operation is not carried out on the second sixteen of the 576 quantised coefficients and, although the sequence of sixteen pseudo-random numbers is generated, the sequence is simply discarded.

8. The lossy compression stage of the MPEG Audio Layer 3 encoding is reversed to give an initial set of 576 digital audio samples. The initial set of 576 digital audio samples are transmitted to a buffer memory from which they are transmitted to a digital-to- analogue converter to produce audio material to be played by the player.

9. Operations 5 to 8 are repeated with subsequent encoded frames of the audio track and subsequent sets of sixteen 32-bit pseudo-random numbers until the entire encoded digital audio track has been decoded.

The authorisation data word fields of the look-up table 124 stored in the hard disk drive 12 initially all contain zero data values. The impairment removal data word generated by the PLD 22 for each track and used to seed the pseudo-random number generator are therefore different from the impairment introduction data words used to seed the pseudo-random number generator of the computer 10. The exclusive OR operation carried out by the microprocessor 80 of the player on the sixteen impaired quantised coefficients uses different pseudo-random numbers from those used by the microprocessor 16 of the computer 10 to impair them. The impairment is therefore not reversed, but merely altered in a pseudo-random fashion, and the low frequency rumbling noise remains when the audio material is played.

In an alternative embodiment of the invention the microprocessor, if it detected that the 32- bit authorization data word corresponding to a track selected by the user of the player was zero, indicating that the user had not purchased the authorization data for that track, could instead of carrying out operation 7 above, simply set the second sixteen of the 576 impaired quantised coefficients to zero. This would result in tinny sounding audio material.

If the user decides to acquire the authorization data for a particular track, he presses an "identify drive" button on the keypad 84, which causes the microprocessor 80 to transmit an "identify drive" command to the hard disk drive 12. The hard disk drive 12 transmits the model number and 64-bit serial number stored on the read-only portion of the hard disk to the microprocessor, which causes the model number and serial number to be displayed on a display device (not shown in Figure 5) of the player.

The user telephones a distributor of audio/video material and informs the distributor of the model and serial number displayed on the display device of the player and the track numbers of the tracks of interest to him. The user makes a payment to the distributor according to the number of tracks of interest to him, for example using a credit card.

The distributor obtains the authorization data requested by the user from the computer 10 by entering the model number and serial number and track numbers provided by the user into the computer 10. The computer retrieves the authorization data for each of the track numbers from the database stored in the hard disk drive 18 and displays them on a display device (not shown in Figure 1). The distributor reads the track numbers and corresponding authorisation data to the user, who writes down the track numbers and authorisation data.

For each track of interest to him, the user enters the track number into the player, presses an "enter authorisation data" button on the keypad 84 and enters the authorisation data for that track. The microprocessor 80 writes the authorisation data to the authorisation data field of the lookup table 124 corresponding to that track. When the user selects that track number in future, the authorisation data retrieved from the look-up table 124 by the microprocessor 80 of the player causes impairment removal data to be generated by the PLD that are identical with the impairment introduction data used to impair the audio material. The impairment of the audio material is therefore reversed and the player plays a restored version of the audio material.

It will be apparent to those skilled in the art that the embodiment of the invention described above could equally well have been implemented using an electrically erasable programmable read-only memory (EEPROM) instead of the hard disk drive 12. In particular some EEPROMs, referred to as "flash" memories, are designed to mimic the behaviour of a hard disk drive, and are indistinguishable from hard disk drives by devices to which they are attached.

It will also be apparent that the above description relates only to one embodiment of the invention, and that the invention encompasses other embodiments as defined by the

foregoing summary of the invention.

Claims

Claims 1. An audio/video material player that has a memory device, a data

processor and data I input means, the memory device having a read-only portion and a read/write portion, the read-only portion having stored in it identification data and the read/write portion having stored in it an impaired version of audio/video material into which a reversible impairment has been introduced using impairment introduction data derived from the identification data i and from authorisation data, the player being operable, in the absence of authorisation data, to play the impaired version of the audio/video material, and the data processor being operable to receive authorisation data from the data input means, to derive impairment removal data from the identification data and the authorisation data, and to use the impairment removal data to reverse the reversible impairment of the audio/video material to enable the player to play a restored version of the audio/video material.
2. A player according to claim 1, wherein the data processor is operable to store the I authorisation data in the read/write portion of the memory device.
3. A player according to claim 2, wherein the data processor is operable to read the authorisation data from the read/write portion of the memory device and the identification data from the read-only portion of the memory device, to derive the impairment removal :. data from the identification and authorisation data and use the impairment removal data to ...

reverse the reversible impairment of the impaired version of the audio/video material stored in the read/write portion of the memory device. . . .
4. A player according to any preceding claim, wherein the identification data stored in the read-only portion of the memory device are substantially unique to the memory device. :
5. A player according to any preceding claim, wherein the player includes algorithm execution means operable in accordance with a randomly generated algorithm to derive the impairment removal data from the identification data and authorization data.
6. A player according to claim 5, wherein the algorithm execution means comprises a i programmable logic device (PLD) that is programmed with the randomly generated algorithm during manufacture of the player.
7. A player according to any preceding claim, wherein the memory device is a hard disk drive or electrically erasable programmable read-only memory (EEPROM).
8. A player according to any preceding claim, wherein the data input means comprises interface means operable to connect the device to a telecommunications network.
9. A player according to any preceding claim, wherein the audio/video material comprises a plurality of audio/video material tracks, into each of which tracks a respective reversible impairment has been introduced using impairment introduction data derived from the identification data of the memory device and authorization data specific to that track.
10. A player according to claim 9, which is operable to overwrite with a user's own material those impaired material tracks stored in the memory device of the player for which the authorization data is unavailable in preference to writing the user's own material : . . to blank portions of the memory device.
11. A player according to any preceding claim, wherein the impairment removal data . used to reverse the reversible impairment of the audio/video material are identical with the impairment introduction data used to introduce the reversible impairment into the material. 4
12. A method of producing an audio/video material player in accordance with any preceding claim, the method comprising the steps of reading identification data from a read-only portion of a memory device, generating authorization data, deriving impairment introduction data from the identification data and authorization data, using the impairment introduction data to introduce a reversible impairment into audio/video material to produce an impaired version of the material, and writing the impaired version of the audio/video material to a read/write portion of the memory device.
13. A method according to claim 12, further comprising the steps of generating random algorithm data, writing the algorithm data to algorithm execution means operable to execute an algorithm determined by the algorithm data, and using the algorithm determined by the algorithm data to derive the impairment introduction data from the identification and authorization data.
14. A method of introducing a reversible impairment into audio/video material, the method comprising the steps of carrying out a lossy compression process on the audio/video material to produce lossy compressed audio/video material, introducing a reversible impairment into the lossy compressed audio/video material to produce impaired lossy compressed audio/video material, and carrying out a lossless compression process on the impaired lossy compressed audio/video material.
15. A method according to claim 14, wherein the lossy compression process comprises the lossy stages of MPEG Audio Layer 3 encoding of digital audio material, which produce an array of 576 quantised coefficients representative of 576 frequency components of the digital audio material, the introduction of the reversible impairment into the lossy me compressed audio/video material comprises carrying out a reversible logical operation on as.

at least a portion of one or more of the 576 quantised coefficients, and the lossless - - compression process comprises the lossless stages of MPEG Audio Layer 3 encoding of the 576 quantised coefficients into which the reversible impairment has been introduced. .e

. . .
16. A method according to claim 15, wherein the reversible logical operation is an exclusive OR operation, which is carried out on the three least significant bits of the second sixteen of the 576 quantised coefficients.
17. A method of reversing a reversible impairment of audio/video material stored in a memory device of an audio/video material player in accordance with the first aspect of the invention to obtain a restored version of the material, the method comprising the steps of reading identification data from a read-only portion of a memory device of an audio/video material player, deriving impairment removal data from the identification data and from authorisation data, and using the impairment removal data to reverse a reversible impairment of audio/video material stored in a read/write portion of the memory device.
18. A method according to claim 17, further comprising the step of using algorithm execution means that has been programmed with a randomly generated algorithm to derive the impairment removal data from the identification data and the authorisation data.
19. A computer program executable by data processing means to perform a method in accordance with any of claims 14 to 16.
20. A computer program executable by a data processor of an audio/video material player in accordance with any of claims 1 to 11 to perform a method in accordance with claim 17 or 18.
21. An audio/video material player substantially as hereinbefore described and with reference to the accompanying drawings. :' I3ee
22. A method of producing an audio/video material player substantially as hereinbefore .

described and with reference to the accompanying drawings. .
23. A method of introducing a reversible impairment into audio/video material substantially as hereinbefore described and with reference to the accompanying drawings.
24. A method of reversing a reversible impairment of audio/video material substantially as hereinbefore described and with reference to the accompanying drawings.