System and method for controlling display of motion picture subtitles in a selected language during play of a software carrier

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This invention relates to the display of subtitles during play of a software (e.g., motion picture) carrier, and more particularly to a technique by which subtitles in multiple languages are recorded on the same carrier with provision for selecting one language for display.

BACKGROUND OF THE INVENTION

The most widespread medium for distributing motion pictures is the videocassette. The conventional practice is to provide only one language soundtrack on each videocassette. Similarly, if subtitles are to be provided, e.g., French language subtitles for an "English" motion picture to be distributed in France, only subtitles in that language will appear. (Subtitles in two languages are possible, but this obviously interferes even more with the video.) This means that different audio and subtitle versions of the same "foreign" motion picture must be prepared for distribution in different countries.

Rather than to dedicate a different dialog-language and subtitle-language version of the same motion picture for each combination of dialog and subtitle languages (if each of 20 dialog languages is to have subtitles in the other 19 languages, 380 different dialog/subtitle versions would be necessary), it would be far more advantageous to provide multiple soundtracks, containing different dialog languages, and multiple language subtitle captions on the same carrier; this would require the production of far fewer versions of the same motion picture. Because of the large storage requirements, however, this has not proven to be practical.

Digitally encoded optical disks are in theory far superior for the distribution of motion pictures and other forms of presentation. Especially advantageous is the use of "compressed video," by which it is possible to digitally encode a motion picture on a disk no larger than the present-day audio CD. While much effort has been expended in developing compressed video systems, less work has been devoted to the provision of multiple soundtracks and multiple subtitles on the same software carrier.

It is therefore an object of this invention to provide a system and method for playing a software carrier, such as an optical disk, on which a motion picture has been recorded accompanied with subtitles in multiple languages. (The provision of multiple dialog language soundtracks, while described, is not claimed herein other than in combination with the provision of multiple subtitle languages.)

SUMMARY OF THE INVENTION

Before summarizing the invention, it is to be appreciated that the present invention contemplates data-efficient storage and recovery of various audio and subtitle presentations, and not just different language movie soundtracks and subtitles. For example, multiple soundtracks and subtitle captions could include teaching and testing versions of the same material, and there could perhaps be teaching and testing versions for multiple levels of expertise. Thus, it is to be understood that the object of the invention is to provide a plurality of subtitle sequences synchronized with a motion picture (video and audio), and not necessarily such sequences which differ only in terms of language. It is also to be understood that the invention is not limited to a particular medium, and it is applicable to tape carriers and all digital storage media, not just the optical disks of the illustrative embodiment of the invention. Nor is the invention limited only to the distribution of motion pictures. For example, in an extreme case, the invention is applicable to the distribution of a library of still pictures, in which case there is no "motion" at all. The terms "subtitle tracks" and "subtitle sequences" thus embrace much more than movie subtitles in different languages, the term "software publisher" thus embraces much more than a motion picture company, and the term "carrier" embraces much more than a digitally encoded optical disk. As used herein, the term "subtitle" refers to any text, displayed anywhere on an image.

The illustrative embodiment of the invention is an optical disk which includes multiple audio tracks and multiple subtitle tracks synchronized with a motion picture track. The user selects one of the audio tracks, the French track, for example, if he wants to hear the French version of the movie. If there is no audio track in his/her language, this selection is not particularly important. What is more significant in such a case is the selection of the subtitle language.

The disk includes within its lead-in section a series of codes which identify the available subtitle languages. There are a maximum of 99 subtitle tracks which may be provided. It is necessary to identify which languages are available on the disk so that the user can control his player to generate subtitles in the desired language, by reading subtitle sequences in a selected track.

Information recorded on the software carrier is recorded in separately identifiable blocks. This is true for both video, all of the synchronized audio, and all subtitles. Each block contains indicia of which subtitle tracks in the block contain update information. In general, once a subtitle caption is generated, it remains in view. It is removed, with or without a new subtitle taking its place, only when new subtitle data is read from the carrier. All it takes is a single bit for each of the subtitle tracks at the beginning of a block to allow the player to determine whether respective language-specific subtitle information is in the block being processed.

Other features of the invention will be described below. For example, a citizen of Spain, who purchases a player and optical disks in Spain, can be assumed to want to see Spanish subtitles of a "foreign" motion picture. Therefore, a player sold in Spain should "default" to play of a Spanish subtitle track if one is available on the disk (assuming that subtitles are desired at all). Only if the default language is not available, or the user actually wants to see subtitles in a different language, should she be required to choose from among the available languages. How the data is stored on software carriers, and how it is accessed and played, will be discussed at length below.

The invention is disclosed in the context of an overall system which offers numerous advantageous features. The entire system is described although the appended claims are directed to specific features. The overall list of features which are of particular interest in the description below include:

Video standard and territorial lock out.

Play in multiple aspect ratios.

Play of multiple versions, e.g., PG-rated and R-rated, of the same motion picture from the same disk, with selective automatic parental disablement of R-rated play.

Encrypted authorization codes that prevent unauthorized publishers from producing playable disks.

Provision of multiple-language audio tracks and multiple-language subtitle tracks on a single disk, with the user specifying the language of choice.

Provision of multiple "other" audio tracks, e.g., each containing some component of orchestral music, with the user choosing the desired mix.

Variable rate encoding of data blocks, and efficient use of bit capacity with track switching and/or mixing, to allow all of the above capabilities on a single carrier.

Further objects, features and advantages of the invention will become apparent upon consideration of the following detailed description in conjunction with the drawing, in which:

FIG. 1 depicts a prior art system and typifies the lack of flexibility in, and the poor performance of, presently available media players;

FIG. 2 depicts the illustrative embodiment of the invention;

FIG. 3 is a chart which lists the fields in the lead-in portion of the digital data track of an optical disk that can be played in the system of FIG. 2;

FIG. 4 is a similar chart which lists the fields in each of the data blocks which follow the lead-in track section of FIG. 3;

FIGS. 5A-5E comprise a flowchart that illustrates the processing by the system of FIG. 2 of the data contained in the lead-in track section of an optical disk being played;

FIG. 6 is a flowchart that illustrates the processing of the data blocks, in the format depicted in FIG. 4, that follow the lead-in section of the track;

FIG. 7A is a state diagram and legend that characterize the manner in which the player of the invention reads only those data blocks on a disk track that are required for the play of a selected version of a motion picture or other video presentation, and FIG. 7B depicts the way in which one of two alternate versions can be played by following the rules illustrated by the state diagram of FIG. 7A;

FIG. 8 depicts symbolically a prior art technique used in compressing the digital representation of a video signal; and

FIG. 9 illustrates the relationships among three different image aspect ratios.

THE PRIOR ART

The limitations of the prior art are exemplified by the system of FIG. 1. Such a system is presently available for playing a single source of program material, usually a VHS videocassette, to generate a video signal conforming to a selected one of multiple standards. A system of this type is referred to as a multistandard VCR, although stand-alone components are shown in the drawing. Typically, a VHS tape 7 has recorded on it an NTSC (analog) video signal, and the tape is played in a VHS player 5. The analog signal is converted to digital form in A/D converter 9, and the digital representations of successive frames are written into video frame store 11. Circuit 13 then deletes excess frames, or estimates and adds additional frames, necessary to conform to the selected standard, e.g., PAL. To convert from one standard to another, it is generally necessary to change the number of horizontal lines in a field or frame (image scaling). This is usually accomplished by dropping some lines, and/or repeating some or averaging successive lines to derive a new line to be inserted between them. The main function of circuit 13, of course, is to convert a digital frame representation to analog form as the video output.

Systems of the type shown in FIG. 1 generally degrade the video output. Conventional videocassettes deliver reduced quality video when they support more than one video standard. One reason is that there is a double conversion from analog to digital, and then back again. Another is that the image scaling is usually performed in a crude manner (deleting lines, repeating lines and averaging lines). There are known ways, however, to perform image scaling in the digital domain without degrading the picture. While not generally used, the technique is in the prior art and will therefore be described briefly as it is also used in the illustrative embodiment of the invention.

To give a concrete example, the PAL standard has 625 lines per frame, while the NTSC standard has 525 lines per frame. Because no part of the image is formed during the vertical retrace, not all of the horizontal line scans in either system are usable for representing image information. In the PAL standard there are nominally 576 lines per frame with image information, and in an NTSC frame there are nominally 483 lines with image information.

To convert from one standard to another, successive fields are first de-interlaced. Then 576 lines are converted to 483, or vice versa, and reinterlaced. How this is done is easy to visualize conceptually. Consider, for example, a very thin vertical slice through a PAL frame. The slice is broken down into its three color components. Image scaling for converting from PAL to NTSC, from a conceptual standpoint, is nothing more than drawing a curve based on 576 PAL pieces of color data and then dividing the curve into 483 parts to derive a piece of data for each horizontal line of the desired NTSC signal. In actuality, this is accomplished by a process of interpolation, and it is done digitally. (Image scaling, in general, may also involve a change in the aspect ratio, for example, in going from HDTV to NTSC, and may require clipping off information at both ends of every horizontal line.)

While prior art systems thus do provide for standards conversion, that is about the extent of their flexibility. The system of FIG. 2, on the other hand, offers unprecedented flexibility in ways not even contemplated in the prior art.

THE ILLUSTRATIVE SYSTEM OF THE INVENTION

The system of FIG. 2 includes a disk drive 21 for playing an optical disk 23. Digital data stored on the disk appears on the DATA OUT conductor 25. The disk drive operation is governed by microprocessor disk drive controller 27. The read head is positioned by commands issued over HEAD POSITION CONTROL lead 29, and the speed of the disk rotation is governed by commands issued over RATE CONTROL conductor 31. Optical disks are usually driven at either constant linear velocity or constant angular velocity. (Another possibility involves the use of a discrete number of constant angular velocities.) Disks of the invention may be driven at constant linear velocity so that the linear length of track taken by each bit is the same whether a bit is recorded in an inner or outer portion of the track. This allows for the storage of the most data. A constant linear velocity requires that the rate of rotation of the disk decrease when outer tracks are being read. This type of optical disk control is conventional. For example, the CD audio standard also requires disks which are rotated at a constant linear rate.

Microprocessor 41 is the master controller of the system. As such, it issues commands to the disk drive controller over conductor 43 and it determines the status of the disk drive controller over conductor 45. The disk drive controller is provided with two other inputs. Block number/pointer analyzer 47 issues commands to the disk drive controller over conductor 49, and BUFFER FULL conductor 51 extends a control signal from OR gate 54 to the disk drive controller. These two inputs will be described below. (In general, although reference is made to individual conductors, it is to be understood that in context some of these conductors are in reality cables for extending bits in parallel. For example, while the output of OR gate 54 can be extended to the disk drive controller over a single conductor 51, block number/pointer analyzer 47 could be connected to the disk drive controller over a cable 49 so that multi-bit data can be sent in parallel rather than serially.)

An important feature of the system of FIG. 2 is that bit information is stored on the disk at a rate which varies according to the complexity of the encoded material. By this is meant not that the number of bits per second which actually appear on the DATA OUT conductor 25 varies, but rather that the number of bits which are used per second varies. Video information is stored in compressed digital form. FIG. 8 shows the manner in which video frames are coded according to the MPEG1 and MPEG2 standards. An independent I-frame is coded in its entirety. Predicted or P-frames are frames which are predicted based upon preceding independent frames, and the digital information that is actually required for a P frame simply represents the difference between the actual frame and its prediction. Bidirectionally predicted B-frames are frames which are predicted from I and/or P frames, with the information required for such a frame once again representing the difference between the actual and predicted forms. (As can be appreciated, fast forward and fast reverse functions, if desired, are best implemented using I-frames.) The number of bits required to represent any frame depends not only on its type, but also on the actual visual information which is to be represented. Obviously, it requires far fewer bits to represent a blue sky than it does to represent a field of flowers. The MPEG standards are designed to allow picture frames to be encoded with a minimal number of bits. Frame information is required at a constant rate. For example, if a motion picture film is represented in digital form on the disk, 24 frames will be represented for each second of play. The number of bits required for a frame differs radically from frame to frame. Since frames are processed at a constant rate, it is apparent that the number of bits which are processed (used) per second can vary from very low values to very high values. Thus when bits are actually read from the disk, while they may be read from the disk at a constant rate, they are not necessarily processed at a constant rate.

Similar considerations apply to any audio stored on the disk. Any data block may contain the bit information required for a variable number of image frames. Any data block may similarly contain the bit information required for a variable time duration of a variable number of even numerous audio tracks. (There is just one physical track. The reference to multiple audio tracks is to different series of time-division slices containing respective audio materials.) The audio tracks contain digital information, which may also be in compressed form. This means that if there is information stored in any data block for a particular audio track, those bits do not necessarily represent the same time duration. It might be thought that the duration of the sound recorded for any audio track corresponding to any picture frames represented in a block would be the duration of the picture frames. However, that is not necessarily true. This means that audio information may be read before it is actually needed, with the reading of more audio information pausing when a sufficient amount has already accumulated or with audio not being included in some data blocks to compensate for the preceding over-supply. This leads to the concept of buffering, the function of audio buffers 53, video buffer 55, pan scan buffer 57, subtitle buffer 59, and OR gate 54 which generates the BUFFER FULL signal.

As each data block is read from the disk, it passes through gate 61, provided the gate is open, and the bit fields are distributed by demultiplexer 63 to the various buffers and, over the COMMAND/DATA line 65, to master controller 41. Each data block in the illustrative embodiment of the invention contains video bit information corresponding to a variable number of picture frames. As discussed above, there may be a large number of bits, or a small number, or even no bits (for example, if the particular disk being played does not represent any video). Successive groups of video data are stored in video buffer 55 separated by markers. Video decoder 67 issues a command over conductor 69 when it wants to be furnished with a new batch of data over conductor 71. Commands are issued at a steady rate, although the number of bits furnished in reply vary in accordance with the number of bits required for the particular frames being processed. The rate at which bits are read from the disk drive is high enough to accommodate frames which require maximal information, but most frames do not. This means that the rate at which data blocks are actually read is higher than the rate at which they are used. This does not mean, however, that a well-designed system should delay reading of a block of data until the data is actually required for processing. For one thing, when data is actually required, the read head may not be positioned at the start of the desired data block. It is for this reason that buffering is provided. The video buffer 55 contains the bit information for a number of successive frames (the actual number depending upon the rate at which bits are read, the rate at which frames are processed, etc., as is known in the art), and video data block information is read out of the video buffer at a constant frame rate determined by video decoder 67. Video data is delivered to the buffer only until the buffer is full. Once the buffer is full, no more information should be delivered because it cannot be stored. When the video buffer is full, a signal on conductor 69 causes the output of OR gate 54 to go high to inform disk drive controller 27 that one of the buffers is full.

Similar remarks apply to the three other types of buffers. (There is a single subtitle buffer 59, a single pan scan buffer 57, and numerous audio buffers 53, the purpose of all of which will be described below.) When any of these buffers is full, its corresponding output causes OR gate 54 to control the BUFFER FULL conductor to go high and to so inform the disk drive controller that one of the buffers is full. Audio buffers 53 and subtitle buffer 59 operate in a manner comparable to that described for video buffer 55. Audio processor decoder 71 issues a command to the audio buffers when it requires audio track data, at which time the audio buffers furnish such data. Similarly, graphics generator 73 retrieves data from subtitle buffer 59, and pan scan processor/vertical scaler 87 receives data from pan scan buffer 57 as will be described below.

When any one of the four buffers is full (which includes any one of the individual buffers within the block 53), the disk drive controller 27 causes the disk drive to stop reading data. Data is not read again until all of the buffers can accept it, i.e., until no buffer is full and conductor 51 goes low. (Conversely, if the buffers are being depleted of data too rapidly, an adjustment in the RATE CONTROL signal on conductor 31 increases the disk speed and thus the rate at which the buffers are filled.)

This discussion of buffering arose from a consideration of the BUFFER FULL input 51 to the disk drive controller 27. The other input which remains to be described is that represented by cable 49. As will be described below, every data block has a serial block number as well as pointer information at its beginning. Circuit 47 reads the serial block number and analyzes the pointer information. The pointer, a serial block number, points to the next data block which should be read. This information is furnished to the disk drive controller over cable 49. It is in this way that the disk drive controller can control positioning of the read head of the disk drive so that the desired data block can be accessed. Many times the wrong block will be read--this is to be expected in the case of a jump to a new block, as is the case, for example, when a jump is made from one track to another when playing a CD audio disk. If the disk drive reads a data block whose serial block number is too high or too low, this is determined by block number/pointer analyzer 47 which then issues a new command over cable 49 to the disk drive controller to cause it to read another block with a lower or higher serial block number respectively. During the time that the read head is positioning itself to read a new block, the data which is read is not actually used. Gate 61 remains closed so that the information is not delivered to the demultiplexer 63 for distribution to the four buffers and to the master controller 41 over the COMMAND/DATA lead. It is only when the correct data block is reached, as determined by circuit 47 analyzing the serial block number at the start of the block, that conductor 75 is pulsed high to open gate 61.

The remainder of the block is then delivered to the demultiplexer. The data bits read from the disk are also delivered to the microprocessor master controller 41 over conductor 77. Each data block contains not only bit information which must be distributed to the various buffers, but also control information, e.g., bits that identify the kind of data actually to be found in the block. The identification bits (flags and the like, as will be described below) are furnished to the master controller so that it is in control of the system at all times. The identification bits are used by the demultiplexer to control data distribution to the various buffers. (The master controller issues commands over conductor 76 to the block number/pointer analyzer 47 which exercise not only general control over this element, but also specific control by causing element 47 to turn off the enabling signal on conductor 75 as is appropriate to prevent full data blocks from entering the demultiplexer if they are not required for subsequent processing.)

The master controller is at the heart of the system and in fact carries out the bulk of the processing to be described below. The user of the player communicates with the master controller via an interface 79, typically a keyboard. The user also is provided with a key and lock mechanism, shown symbolically by the numeral 81, which is referred to herein as the "parental lock" option. If the lock is turned on, then R-rated motion pictures will not play. The manner in which this is controlled by bits actually represented on the disk will be described below. If the lock is on, and only an R-rated picture is on the disk, a disabling signal on PARENTAL LOCK CONTROL conductor 83 closes gate 61. No data bits are transmitted through the gate and the disk cannot be played. As will become apparent below, if the disk also has on it a version of the film which is not R-rated, it will play if it is selected by the viewer. Although the parental lock feature is shown as requiring the use of an actual key and lock, it is to be understood that the feature can be implemented by requiring keyboard entries known only to a child's parents. The manner of informing the master controller that R-rated versions of a motion picture should not be viewed is not restricted to any one form. Just as physical keys and coded keys are alternatively used to control access to a computer, so they can be in the system of FIG. 2. What is important is the way in which two different versions can be represented on the same disk (without requiring the full version of each), and how the system determines whether a selected version may be played in the first place. This will be described below.

Master controller 41 includes several other outputs which have not been described thus far. Conductor 85 represents a MASTER CLOCK bus which is extended to all of the sub-systems shown in FIG. 2. In any digital system, a master clock signal is required to control the proper phasing of the various circuits. The six other outputs of the master controller are extended to demultiplexer 63, audio processor decoder 71, pan scan processor/vertical scaler 87, video frame store, interlace and 3:2 pulldown circuit 89, graphics generator 73, and sync generator and DVA converter 92. These are control leads for governing the operations of the individual circuit block.

Audio processor decoder 71 processes the data in buffers 53 and derives individual audio analog signals which are extended to an amplifier/speaker system shown symbolically by the numeral 91. Video decoder 67 derives a DIGITAL VIDEO signal on conductor 93 from the compressed video data which is read from buffer 55. The digital video is fed to pan scan processor/vertical scaler 87 frame by frame. The particular video coding/decoding that is employed is not a feature of the present invention. A preferred standard would be one along the lines of MPEG1 and MPEG2, but these are only illustrative. The same is true of the audio track coding. The present invention is not limited to particular coding methods.

The operations of circuits 57 and 87 can be best understood by first considering the symbolic drawing of FIG. 9. The digital information which is stored on the optical disk in the preferred embodiment of the invention characterizes frames having a "master" aspect ratio of 16:9, the so-called "wide screen" image. The master aspect ratio is shown on the upper left in FIG. 9. If the ultimate analog signal to be displayed on the user's television receiver requires this aspect ratio, and the number of horizontal scan lines with picture information (as opposed to horizontal scan lines which occur during vertical retrace) corresponds with the number of horizontal lines represented by the video bit information stored on the disk, then the generation of the video analog signal is straightforward. But if the television receiver of the user accommodates a TV signal having a 4:3 aspect ratio, and the master aspect ratio on the disk is 16:9 rather than 4:3, then there are two choices. One is to display the original picture in "letter box" font:. As depicted on the right side of FIG. 9, what is done in this case is to vertically compress uniformly a master image so that its horizontal dimension fits into the confines of the television receiver. This r