Abstract:
A formatting apparatus authenticates an information signal prior to mass duplication of the signal by analyzing the signal to detect the presence or absence of a security signal therein, inserting a security signal into the information signal, and recording the modified signal only if no security signal was detected.

Description:
This application is a continuation of U.S. application Ser. No. 08/881,820, filed Jun. 24, 1997 now U.S. Pat. No. 6,115,533, which is a divisional of application Ser. No. 08/705,306, filed Aug. 29, 1996 now Pat. No. 5,703,859. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a method for protecting digital data from unauthorized mass duplication. More specifically, this invention relates to a method for copy protecting digital video signals recorded on a storage medium, such as a compact disc. 
     The recent development of consumer electronics incorporating devices for the reproduction of digitally-recorded audio and video data has resulted in the corresponding development of a vast consumer market for digitally-recorded media. Such digitally-recorded media are available in a number of different forms, including optical disc, magnetic disc, magneto-optical disc, magnetic tape, cartridge, and the like. Commonly, many of these forms of digitally-recorded media are available for sale or rental. Additionally, consumers may access and retrieve for storage digital audio and video data from cable systems, computer networks, satellite transmission systems, and the like. 
     Generally, prerecorded digital media contain a complete and virtually error-free duplicate of original data reproduced from an original digital master recording. As is well known in the art, digital data stored on a prerecorded digital medium may be reproduced many times without significantly affecting the quality of the stored data. Hence, a prerecorded digital medium may itself be utilized as a template from which many additional copies of digital data may be reproduced and recorded on other digital media. 
     The ease with which such reproduction and recording operations may occur and the high quality of the resulting recordings has facilitated the development of significant efforts to produce and distribute counterfeit prerecorded digital media. Although counterfeiting may occur in small volumes through the use of consumer recording/reproducing devices, a more significant problem has arisen from the use of mass production recording devices. In the optical disc industry, optical discs are mass produced with a formatting device, termed a “formatter”, which reproduces digital data from a master recording and records the reproduced data onto an “original” disc. A stamping template, “stamper”, is made from this “original” disc. The “stamper” thus created, may then be used to produce large numbers of optical discs, e.g. ROM discs, bearing the original digital data. Hereinbelow, the mass produced optical discs will be referred to as “retail discs.” 
     At present, it is difficult, if not impossible, for an optical disc producer to determine the authenticity of or legal title to a particular master version of digital data provided by a third party. For example, a counterfeiter may bring an illegally obtained master recording, “original” disc, or “stamper”, or even a retail disc, to an optical disc producer for mass reproduction of the recorded digital data. Unable to verify the authenticity of or legal title to the digital data supplied by the counterfeiter, the optical disc producer may unwittingly mass produce optical discs bearing the counterfeiter&#39;s digital data. Such counterfeit optical discs have the potential to be indistinguishable from retail discs produced under proper authority from legal master recordings. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide apparatus for authenticating a digital recording prior to mass duplication of the recording. 
     Another object of the present invention is to provide formatting apparatus for determining the authenticity of a digital recording prior to mass duplication of the recording. 
     Still another object of the present invention is to provide formatting apparatus for inhibiting the mass duplication of a digital recording purchased at retail. 
     Yet another object of the present invention its to imbed security data into a digital recording to prevent mass duplication of that recording. 
     In accordance with an aspect of the present invention, a formatting device for the authentication and mass duplication of an information signal recorded on a storage medium is provided. The device includes a first receiving device for receiving the information signal and a second receiving device for receiving a key signal. A key signal detection device, analyzes the information signal to detect the key signal in the information signal. A key insertion device, inserts the key signal into the information signal to produce a modified information signal. A recording device records the modified information signal if the key signal is not detected in the information signal and inhibits the recording of the modified information signal if the key signal is detected in the information signal. 
     According to another aspect of the present invention, a method for the authentication and mass duplication of an information signal recorded on a storage medium is provided. The method includes the steps of: receiving the information signal; receiving a key signal; analyzing the information signal to detect the key signal in the information signal; inserting the key signal into the information signal to produce a modified information signal; recording the modified information signal if the key signal is not detected in the information signal; and inhibiting the recording of the modified information signal if the key signal is detected in the information signal. 
     Other objects, features, and advantages according to the present invention will become apparent from the following detailed description of illustrated embodiments when read in conjunction with the accompanying drawings in which the same components are identified by the same reference numerals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a procedural diagram of a copy protection methodology according to an embodiment of the present invention; 
     FIG. 2A is a data area diagram of a video sequence data area; 
     FIG. 2B is a data area diagram of a extension-and-user-data area; 
     FIG. 2C is a data area diagram of a user-data data area; 
     FIG. 2D is a data area diagram of a group-of-pictures-header data area; 
     FIG. 3A is a block diagram of an MPEG layer structure; 
     FIG. 3B is a data area diagram of a slice data area; 
     FIG. 3C is a data area diagram of a macroblock data area; 
     FIG. 3D is a data area diagram of a macroblock-modes data area; 
     FIGS. 4A,  4 B and  4 C are data area diagrams of macroblock type data areas; 
     FIG. 5 is a block diagram of an encoder according to certain embodiments of the present invention; 
     FIG. 6 is a block diagram of a formatter according to certain embodiments of the present invention; 
     FIGS. 7 and 8. are procedural diagrams of a key data insertion point selection methodology; 
     FIG. 9 is a diagram of a multibit key data; 
     FIG. 10 is a block diagram of an encoder according to another embodiment of the present invention; and 
     FIG. 11 is a block diagram of a formatter according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 schematically illustrates a copy protection methodology  100  according to the present invention. According to the copy protection methodology  100 , an original source  102  of information is digitally recorded to produce a legal master tape  104  and a legal master disc  106 . The recording process may occur at a broadcasting station, a sound studio, a video production facility, or the like. 
     The original source  102  may include audio signals, video signals, text data, digital data, and the like, which may be encoded or compressed. For example, video signals may be processed according to an MPEG standard. Legal master tape  104  is preferably a magnetic tape and legal master disc  106  is preferably a high-density magneto-optical disc. Of course, tape  104  and disc  106  may each be substituted with any suitable storage medium, such as a semiconductor memory, a magnetic disc, an optical disc, or the like. 
     The legal master tape  104  or the legal master disc  106  is supplied to an optical disc producer having a formatter  108 . Formatter  108  reproduces the digital data corresponding to the original source information from the legal master and incorporates key data into the reproduced digital data. The modified digital data, incorporating key data, is recorded on mass quantities of optical discs intended for retail sale (retail disc  110 ). The key data serves to distinguish the digital data recorded on retail disc  110  from the digital data recorded on legal master tape  104  or legal master disc  106 . 
     A consumer may reproduce the digital data stored on retail disc  110  with a disc player  112 . The reproduced digital data may be displayed to the consumer via a display (not shown) coupled to disc player  112 . The inclusion of key data in the digital data reproduced from retail disc  110  does not significantly affect the reproduction quality of the digital data corresponding to the original source information. Preferably, the incorporation of key data into the digital data corresponding to the source information does not result in flaws in the display of such digital data which would be perceptible to the consumer. 
     In the hands of a counterfeiter, digital data stored on retail disc  110  may be reproduced and recorded on an illegal master, such as illegal master disk  114  and illegal master tape  116 . Illegal master disc  114  may comprise a high-density magneto-optical disc and illegal master tape  116  may comprise a magnetic tape. Alternatively, disc  114  and tape  116  may each be substituted with any suitable storage medium, such as a semiconductor memory, a magnetic disc, an optical disc, or the like. 
     The counterfeiter may then present retail disc  110 , illegal master disc  114 , or illegal master tape  116  to an optical disc producer, having a formatter  108 , for mass duplication of the data stored thereon. Formatter  108  reproduces data from the storage medium supplied by the counterfeiter and detects key data in the reproduced data. The presence of key data indicates to the optical disc producer that the storage medium supplied by the counterfeiter is not an authorized master for the data stored thereon. Accordingly, the optical disc producer refuses to mass produce for the counterfeiter optical discs bearing such data. Specifically, formatter  108  may itself inhibit any duplication of data stored on a recording medium when key data is detected on the recording medium. 
     Conversely, when formatter  108  reproduces data from a storage medium, such as legal master tape  104  or legal master disc  106 , which does not have key data stored thereon, formatter  108  does not detect any key data. The absence of key data indicates to the optical disc producer that the storage medium is an authorized master for the data stored thereon. However, the optical disc producer will not know whether the authorized master has been submitted for duplication by its legal owner (e.g. the legal master may have been stolen). 
     An optical disc producer may choose to ignore: the presence of key data on a storage medium supplied by a counterfeiter and proceed to duplicate data stored upon that storage medium. Such duplication results in the production of counterfeit discs bearing unauthorized copies of the digital data. 
     The present invention is particularly suited for use in conjunction with video data encoded according to an MPEG standard. FIG. 2A illustrates a video sequence data area  200  defined in accordance with an MPEG standard. 
     In a first embodiment of the present invention, key data is stored in a data area defined for the storage of user data, video sequence data area  200  includes an extension-and-user-data data area  202 . FIG. 2B illustrates extension-and-user-data data area  202  which includes a user-data data area  204 . FIG. 2C illustrates user-data data area  204  which may be utilized to store key data. In FIG.  2 C and in certain subsequent drawings, diagonal hatching is used to highlight data areas where key data may be stored. 
     In a second embodiment of the present invention, key data is stored in a data area defined for the storage of header data. Video sequence data area  200  includes a group-of-pictures-header data area  206 . FIG. 2D illustrates group-of-pictures-header data area  206  which includes a time-code data area  208 . Key data may be stored in time-code data area  208  while information corresponding to time code data may be stored in another data area. In an application where a group-of-pictures includes 12 frames of video data, key data is preferably recorded once in a time-code data area  208  for each group-of-pictures. 
     In a third embodiment of the present invention, key data is stored in a data area defined for the storage of quantization data. FIG. 3A illustrates a layer structure  300  of data storage areas according to an MPEG standard. Layer structure  300  includes a sequence layer  302 , a group-of-pictures (GOP) layer  304 , a picture layer  306 , a slice layer  308 , a macroblock (MB) layer  310 , and a block layer  312 . Sequence layer  302  includes a sequence header data area (SH) and a group of pictures data area (GOP). 
     In GOP layer  304 , each GOP data area includes an intra-coded frame (I frame), a number of predictively-encoded pictures (P pictures), and a number of bidirectionally-predictively-encoded pictures (B pictures). In picture layer  306 , each picture includes a number of slice data areas  314 . In slice layer  308 , each slice data area  314  includes a number of macroblocks. 
     In macroblock layer  310 , each macroblock includes a number of blocks of pixel data. For example, brightness data may be stored as four blocks of pixel data and color difference data (Cb, Cr) may be stored as one block of pixel data. In a preferred quantization operation, each block of pixel data is transformed according to a discrete cosine transform (DCT) and the resulting DCT coefficients are quantized. Different levels of quantization may be achieved, each quantization level corresponding to a particular quantization step. 
     Alternatively, in an NTSC-compatible implementation, also shown in FIG. 3A, a picture layer  306  includes a screen of source input format (SIF) which includes 240 lines. E:ach line includes 352 pixels. The pixels are organized into macroblocks of 16×16 pixels. 
     FIG. 3B illustrates a slice data area  314  which includes a quantiser-scale-code (SQUANT) data area  316 . SQUANT data area  316  is defined to store a quantization level for each slice data area  314 . However, instead of storing a qfaantization level, SQUANT data areas  316  may store key data. The quantization level information may be stored on a block-by-block basis in each macroblock. 
     FIG. 3C illustrates a macroblock data area  318  which includes a macroblock-modes data area  320  and a quantiser-scale code (MQUANT) data area  322 . Quantization level information may be stored in each MQUANT data area  322  and, therefore, different macroblocks within a slice may be compressed according to different levels of quantization. 
     FIG. 3D illustrates a macroblock-modes data area  320  which includes a macroblock-type data area  400 . The particular arrangement of macroblock-type data area  400  depends upon the type of picture of which it is a part. FIG. 4A illustrates a macroblock-type data area  402  for an I frame which includes a macroblock-quant data area  408 . FIG. 4B illustrates a macroblock-type data area  404  for a P frame which includes a macroblock-quant data area  408 . FIG. 4C illustrates a macroblock-type data area  406  for a B frame which includes a macroblock-quant data area  408 . 
     When quantization level information is stored in a particular MQUANT data area  322 , a positive “1” flag is stored in the macroblock-quant data area  408  in the macroblock-type data area  400  (e.g. area  402 , area  404 , or area  406 ) of the corresponding macroblock-modes data area  320 . The positive “1” flag indicates that quantization level information has been stored in the corresponding MQUANT data area  322 . 
     To replace the storage of quantization level information in a SQUANT data area  316 , the MQUANT data area  322  of one or more macroblock data areas  318  in the corresponding slice can be utilized to store such quantization level information for the entire slice or for a number of constituent macroblocks. 
     The above-described first, second, and third embodiments of the present invention may be rendered ineffective by a counterfeiter who deletes, overwrites, or otherwise modifies the stored key data. Alteration of the stored key data may not be detectable as it may not adversely affect reproduction and display of the associated digital data, e.g. original source information. 
     FIG. 5 illustrates an encoder  500  for recording original source information  102  to produce a master recording, such as legal master disc  106 , which is compatible with the key data encoding methods of the three embodiments described hereinabove. Encoder  500  includes a frame memory  502 , addition circuits  504  and  518 , a DCT circuit  506 , a quantization circuit  508 , a variable length coding (VLC) circuit  510 , a motion vector detection circuit  512 , a prediction memory  514 , a motion compensation circuit  516 , a dequantization circuit  520 , and an inverse discrete cosine transform (IDCT) circuit  522 . 
     Each of frame memory  502  and prediction memory  514  is a conventional memory device, such as a semiconductor memory, a magnetic tape, a magnetic disc, and the like. Addition circuit  504  is a signal combiner for combining signals by addition, subtraction and the like. Addition circuit  518  is a signal combiner for combining signals by addition and the like. DCT circuit  506  is a discrete cosine transform circuit for transforming data according to a discrete cosine transform method. Quantization circuit  508  is a quantizer for compressing data by a quantization method. Variable length coding circuit  510  is an encoder for variable length encoding data. 
     Motion vector detection circuit  512  is a processing circuit for determining motion vectors in data. Motion compensation circuit  516  is a processing circuit for motion compensating data. Dequantization circuit  520  is a dequantizer for dequantizing quantized data. Inverse discrete cosine transform circuit (IDCT)  522  is transform circuit for processing data according to an inverse discrete cosine transform method. 
     Original source information  102 , such as a digital video signal, is supplied to frame memory  502 . Memory  502  stores the original source information  102  and supplies the original source information  102  to addition circuit  504  and to motion vector detection circuit  512 . Addition circuit  504  combines the original source information with motion compensation information supplied from prediction memory  514  and supplies the resulting combination to DCT circuit  506 . Preferably, addition circuit  504  subtracts the motion compensation information from the original source information. Specifically, where the original source information comprises an I frame, addition circuit  504  passes the I frame directly to DCT circuit  506 . Where the original source information comprises a P frame or a B frame, addition circuit subtracts motion compensation information supplied from prediction memory  514  from the frame and supplies the difference data to DCT circuit  506 . 
     Motion vector detection circuit  512  processes the original source information  102  to determine motion vector information. Motion vector information is supplied to motion compensation circuit  516 . 
     DCT circuit  506  transforms the signal supplied by circuit  504  to produce DCT coefficient data which is supplied to quantization circuit  508 . Preferably, DCT circuit SOE; converts each block of data in each macroblock into DCT coefficients Coeff [u][v]. Further details regarding the DCT processing are provided in conjunction with the discussion of FIG.  7 . Quantization circuit  508  quantizes the DCT coefficient data to produce quantized data which is supplied to VLC circuit  510  and to dequantization circuit  520 . Preferably, quantization circuit  508  converts DCT coefficients Coeff[u] [v] into quantization levels QF[u][v]. The quantization levels QF[u][v] are zigzag scanned as explained in conjunction with FIG.  8 . 
     Dequantization circuit  520  dequantizes the quantized data to produce unquantized data which is supplied to :IDCT circuit  522 . IDCT circuit  522  transforms the unquantized data to produce digital data which is supplied to addition circuit  518 . Addition circuit  518  combines the digital data with motion compensation information supplied from prediction memory  514  to recover original source information and supplies the recovered original source information to motion compensation circuit  516 . 
     Motion compensation circuit  516  processes the recovered original source information in accordance with the motion vector information supplied by motion vector detection circuit  512  to produce motion compensation information, such as a motion predictive image. The motion compensation information is stored in prediction memory  514  for supply to addition circuits  504  and  518 . 
     VLC circuit  510  encodes quantized data supplied by quantization circuit  508  to produce variable-length coded data which are supplied for recording on a master storage medium, such as a legal master disc or a legal.master tape. In accordance with the first embodiment, VLC circuit  510  incorporates user-data data areas in the variable-length coded data. In accordance with the second embodiment, VLC  510  incorporates time-code data areas in the variable-length coded data. In accordance with the third embodiment, VLC  510  incorporates SQUANT data areas in the variable-length coded data. 
     FIG. 6 illustrates a formatter  600  for mass duplication of digital data reproduced from a master recording produced by encoder  500 . Formatter  600  includes a key memory  602 , a variable-length-decoder parser  604 , a key insertion circuit  606 , a recording apparatus  608 , a detection circuit  612 , a control circuit  614 , and a display apparatus  616 . 
     Key memory  602  is a conventional memory device, such as a semiconductor memory, a magnetic tape, a magnetic disc, and the like. Variable-length-decoder (VLD) parser  604  is a circuit for searching a stream of variable-length coded data to determine the positions of particular portions of data. Key insertion circuit  606  is a data insertion circuit for writing data into a stream of digitized data. 
     Recording apparatus  608  is a conventional recording apparatus for recording digital data on a storage medium such as an optical disc, a magneto-optical disc, a magnetic tape, a magnetic disc, a semiconductor memory, and the like. Detection circuit  612  is a circuit for recognizing the presence or absence of key data in a certain portion of data. Control circuit  614  is a control processor device, such as a microprocessor, for controlling the operation of a display and a recording apparatus. Display apparatus  616  is a display device for displaying predetermined visual images, such as text, to a user. 
     Digital data reproduced from a master recording is supplied to VLD parser  604 . VLD parser  604  supplies the reproduced digital data to key insertion circuit  606  and analyzes the reproduced digital data to locate certain data areas incorporated into the reproduced digital data, e.g. data areas where key data may be stored, as indicated by the address information. In the first embodiment of the present invention, VLD parser  604  detects user-data data areas in the reproduced digital data and supplies position information regarding the position of the detected user-data data areas to key insertion circuit  606 . In the second embodiment of the present invention, VLD parser  604  detects time-code data areas in the reproduced digital data and supplies position information regarding the position of the detected time-code data areas to key insertion circuit  606 . In the third embodiment of the present invention, VLD parser  604  detects SQUANT data areas in the reproduced digital data and supplies position information regarding the position of the detected SQUANT data areas to key insertion circuit  606 . Optionally, VLD parser  604  may extract data stored in the detected data area, variable-length decode such data, and supply the decoded extracted data to key insertion circuit  606 . 
     VLD circuit  604  extracts data at the addressed location and supplies the extracted data to detection circuit  612 . Detection circuit  612  analyzes the extracted data to determine the presence or absence of key data. The result of the determination is supplied to control circuit  614 . Specifically, detection circuit  612  may read a portion of the extracted data and supply the read data to control circuit  614 . 
     Control circuit  614  controls the operation of display apparatus  616  and the operation of recording apparatus  608  in accordance with the detection result obtained by detection circuit  612 . As key data may be represented by a number of detection results, control circuit  614  may collect and analyze together a number of detection results from detection circuit  612  to determine the presence or absence of key data. Key memory  602  supplies reference key data to key insertion circuit  606  and to control circuit  614 . 
     Preferably, control circuit  614  compares the detection result(s) supplied by detection circuit  612  with the reference key data. If the reference key data corresponds to the detection result(s) then key data has been detected; otherwise, key data has not been detected. If key data is not detected, control circuit  614  controls display apparatus  616  to display a. predetermined display indicating to a user that no key data has been detected, e.g. that the reproduced data has been reproduced from a legal master, and controls recording apparatus  608  to record the reproduced digital data. If key data is detected, control circuit  614  controls display apparatus  616  to display a predetermined display indicating to a user that key data has been detected and controls recording apparatus  608  to inhibit recording of the reproduced digital data. 
     Key insertion circuit  606  inserts or otherwise writes key data into the reproduced digital data at the location indicated by the position information supplied by VLD parser  604 . For example, key data may be written into a user-data area, a time-code data area, a SQUANT data area, or the like. Optionally, key insertion circuit  606  inserts or otherwise writes key data into-the decoded extracted data, variable-length encodes such data, and incorporates such data into the reproduced digital data. 
     Key insertion circuit  606  supplies the modified digital data to recording apparatus  608 . Under the control of control circuit  614 , recording apparatus  608  may record the modified digital data onto an original storage medium, such as optical disc  610 , or inhibit such recording. From the original storage medium a stamper may be produced for the mass production of storage media bearing the modified digital data. In this manner, storage media, such as optical discs, are produced with key data recorded thereupon. 
     According to a fourth embodiment of the present invention, key data is stored in a data area defined for the storage of digital data corresponding to original source information. For example, key data may be stored in al data area defined for the storage of video data, such as pixel data. More specifically, key data may be coded as a fixed length code and stored in data area defined for the storage of pixel data. 
     FIGS. 7 and 8 illustrate the selection of key data insertion points according to the present invention. As shown, from among a group of pictures containing “N” pictures, a single B frame is selected as the recipient of key data. Of course other frames may be selected to hold key data; however, it is preferred that a B frame store such data to minimize error caused by the displacement of video data with key data. In certain slices of the selected frame, a number of macroblocks are selected to receive key data. (The selected macroblocks have been depicted as dark rectangles.) One of the blocks in a selected macroblock is further selected to receive key data. 
     The selected block, preferably comprised of an 8×8 array of pixels, is discrete-cosine transformed to produce DCT coefficients Coeff[u][v], shown in FIG.  8 . DCT coefficients Coeff[u][v] are quantized to produce quantization levels QF[u][v]. Quantization levels QF[u][v] are zigzag scanned (scan[ 0 ] to scan [ 63 ]) beginning with the quantization level which includes a DC component and ending with quantization levels including higher frequency components. The quantization level QF[ 7 ][ 7 ], scan[ 63 ], corresponding to the highest frequency component, is selected as the data area for insertion of key data. 
     To insert key data into the selected data area, it is preferred that the value stored in the selected data area is modified such that the second least significant bit of such value equals logical “1”. This insertion of key data may be achieved with a logical OR operation, e.g. QF[ 7 ][ 7 ]=QF [ 7 ][ 7 ] OR 2. Preferably, the least significant bit of the value stored in the selected data area is used to actually store the key data. 
     Further, the data located in selected data area QF[ 7 ][ 7 ], scan[ 63 ], is coded as an escape code. Coding this data as an escape code-ensures that the data will be included in the block in a fixed length code (FLC). As shown, an escape code is formed as a fixed length code that preferably include;s a six-bit Escape_code data area, a six-bit RUN data area, and a 12-bit Level data area. The value stored in the Escape_code data area identifies the codeword as an escape code. The value stored in the RUN data area represents the number of quantization coefficients having a certain value, e.g. zero. The value stored in the Level data area represents the value of non-zero quantization coefficients. 
     The insertion of key data is compatible with escape coding according to an MPEG standard since the standard merely requires that the value stored in the Level data area of an escape code may not equal zero. By setting the second least significant bit in the Level data area to a logical one value, the value stored in the Level data area will be nonzero always. 
     Further, since only the two least significant bits of the Level data area are used for the storage of key data, the resulting introduction of error in the display of the corresponding image will be generally imperceptible to the ordinary viewer. 
     According to the above-described method, the least significant bit of a particular data area in one block of video data is used to store key data. To incorporate key data comprising a multiple bit code, multiple blocks of video data may be used to store individual bits of the multiple bit code. Of course, each block may be from the same or a different: slice of data, frame of data, or the like. FIG. 9 illustrates the concatenation of “n” individual bits obtained from “n” blocks, respectively, to form “n”-bit key data. 
     FIG. 10 illustrates an encoder  1000  for recording original source information  102  to produce a legal master, such as legal master disc  106 , which is compatible with the key data encoding methods of the fourth embodiment described hereinabove. Encoder  1000  includes a frame memory  502 , addition circuits  504  and  518 , a DCT circuit  506 , a quantization circuit  5081 , a motion vector detection circuit  512 , a prediction memory  514 , a motion compensation circuit  516 , a dequantization circuit  520 , and an inverse discrete cosine transform (IDCT) circuit  522  which have the same construction and function as the correspondingly numbered elements previously described. Encoder  1000  further includes a pattern ROM  1002 , a logic OR circuit  1004 , and a VLC circuit  1006 . 
     Pattern ROM  1002  is a conventional storage device, such as a semiconductor memory or the like, for storing address information. Alternatively, pattern ROM  1002  may be replaced with a source of variable address information, such as an address calculating device, a random access memory device, or the like, for providing different address information. Logic OF, circuit  1004  is a circuit for modifying certain portions of a signal to have a specific content, such as a logical “1”. VLC circuit  1006  is a variable length encoding device for encoding quantized data according to a variable-length encoding method. 
     Processing of original source information  102  by frame memory  502 , addition circuit  504 , DCT circuit  506 , anal quantization circuit  508  occurs as described above. However, in encoder  1000 , quantization circuit  508  supplies the quantized data to OR circuit  1004 . Pattern ROM  1002  supplies address information to OR circuit  1004  and to VLC circuit  1006  regarding a particular portion of quantized data. Preferably, pattern ROM  1002  supplies information identifying a particular block or blocks of quantized data. 
     In accordance with the address information supplied by pattern ROM  1002 , OR circuit  1004  modifies a particular portion of the quantized data supplied by quantizaton circuit  508  to facilitate storage of key data. Preferably, OR circuit  1004  modifies the second least significant bit of the last codeword in the block designated by pattern ROM  1002 , e.g. QF[ 7 ][ 7 ] of scan [ 63 ]. The second least significant bit is preferably modified to have a value equal to logical “1”. The modified quantized data is supplied to VLC circuit  1006  and to dequantization circuit  520 . 
     VLC circuit  1006  encodes the modified quantized data supplied by OR circuit  1004  to produce variable-length coded data which are supplied for recording on a master storage medium, such as a legal master disc or a legal master tape. Preferably, in accordance with address information supplied by pattern ROM  1002 , VLC circuit  1006  encodes as an ESCAPE code a particular portion of the quantized data supplied by OR circuit  1004 , e.g. QF[ 7 ][ 7 ] of scan [ 63 ] of the block designated by pattern ROM  1002 . The ESCAPE code is structured as Escape_code+RUN+Level as shown in FIG.  8 . 
     Processing of the modified quantized data by dequantization circuit  520 , IDCT circuit  522 , adding circuit  518 , and motion compensation circuit  516 , along with motion vector processing by motion vector detection circuit  512  and motion compensation information storage by prediction memory  514 , is achieved according to the method of operation previously described in connection with encoder  500 . 
     FIG. 11 illustrates a formatter  1100  for mass duplication of digital data reproduced from a master recording produced by encoder  1000 . Formatter  1100  includes a key memory  602 , a recording apparatus  608 , a control circuit  614 , and a display apparatus  616  which have the same construction and function as the correspondingly numbered elements previously described. Formatter  1100  further includes a variable-length-decoder (VLD) parser  1102 , a pattern ROM  1104 , a key insertion circuit  1106 , and a detection circuit  1108 . 
     Variable-length-decoder (VLD) parser  1102  is a circuit for searching a stream of variable-length coded data to determine the positions of particular portions of data. Pattern ROM  1104  is a conventional storage device, such as a semiconductor memory or the like, for storing address information. Preferably, pattern ROM  1104  stores the same address information as is stored in pattern ROM  1002 . Alternatively, pattern ROM  1104  may be replaced with a source of variable address information, such as an address calculating device, a random access memory device, or the like, for providing different address information. Key insertion circuit  1106  is a data insertion circuit for Meriting data into a stream of digitized data. Detection circuit  1108  is a circuit for recognizing the presence or absence of key data in a certain portion of data. 
     Digital data reproduced from a master recording and address information supplied by pattern ROM  1104  is supplied to VLD parser  1102 . VLD parser  1102  supplies the reproduced digital data to key insertion circuit  1106  and analyzes the reproduced digital data to locate certain data areas incorporated into the reproduced digital data, e.g. data areas where key daiza may be stored, as indicated by the address information. Preferably, address information supplied by pattern ROM  1104  pertains to the position of data located at QF[ 7 ][ 7 ] in scan [ 63 ] of a particular data block indicated by the address information. 
     VLD parser  1102  detects data located at QF[ 7 ][ 7 ] in scan [ 63 ] of the data block indicated by the address information and supplies position information regarding the position of the detected data areas to key insertion circuit  1106 . Optionally, VLD parser  1102  may extract data stored in the detected data area, variable-length decode such data, and supply the decoded extracted data to key insertion circuit  1106 . VLD parser  1102  extracts data at the addressed location and supplies the extracted data to detection circuit  1108 . 
     Detection circuit  1108  analyzes the extracted data to determine the presence or absence of key data. Preferably, detection circuit  1108  determines whether the second least significant bit of QF[ 7 ][ 7 ] of scan [ 63 ] of the extracted data is a logical “1”. The result of the determination, or simply a value from the extracted data, is supplied to control circuit  614 . 
     Key memory  602  supplies reference key data to key insertion circuit  1106  and to control circuit  614 . Key insertion circuit  1106  inserts or otherwise writes key data into the reproduced digital data at the location indicated by the position information supplied by VLD parser  1102 . For example, key data may be written into QF[ 7 ][ 7 ] of scan [ 63 ] of a particular block. Optionally, key insertion circuit  1106  may insert or otherwise write key data into decoded extracted data, variable-length encode such data, and incorporate such data into the reproduced digital data. Key insertion circuit  1106  supplies the modified digital data to recording apparatus  608 . 
     Control circuit  614 , recording apparatus  608 , and display apparatus  616  operate in a manner corresponding to that previously described in connection with formatter  600 . In this manner, key data is incorporated into data areas defined for the storage of original source information, e.g. video signals, audio signals, text data, or the like. The incorporation of key data into such data areas hinders efforts to detect, remove, or modify such data. 
     Each of the embodiments described hereinabove is compatible with an MPEG video standard. Also, by incorporating a key data insertion device in the formatter, each embodiment achieves a greater security function as compared to devices which may insert security data during the data encoding process, e.g. production of a master recording. Further, since formatting devices tend to be more expensive and, therefore, less prevalent than encoding devices, enforcement of data duplication rights at the formatting stage of production, through implementation of the present invention, rather than at the encoding stage of production, is more likely to be successful. 
     Although illustrative embodiments of the present invention and modifications thereof have been described in detail herein, it is to be understood that this invention is not limited to these precise embodiments and modifications, and that other modifications and variations may be affected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.