Abstract:
A method and apparatus are provided for creating and recording management information for digital data streams, and for reproducing data using the management information. The method for reproducing data from a recording medium includes receiving an access time for accessing data from the recording medium, searching for a target entry point based on the access time by using access time entries, and searching for a target object unit by using the target entry point and object unit entries. The access time entries and the object unit entries are management information stored on the recording medium.

Description:
The present application is a continuation of U.S. patent application Ser. No. 09/435,362 filed on Nov. 8, 1999 (now U.S. Pat. No. 6,801,711 issued on Oct. 5, 2004) for which priority is claimed under 35 U.S.C. § 120; and the present application claims priority of Patent Application No. 98-48097 filed in Republic of Korea on Nov. 8, 1998, under 35 U.S.C. § 119. The entire contents of each of these applications are herein fully incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method and apparatus for recording received digital data streams on a recording medium and creating and recording management information for the recorded digital data streams. The present invention also relates to a method and apparatus for reproducing data from a recording medium using the recorded management information. 
   2. Description of the Related Art 
   In conventional analog television broadcast, video signals are transmitted over the air or through cables after being AM or FM modulated. With the recent rapid advance of digital technologies such as digital image compression or digital modulation/demodulation, standardization for digital television broadcast is in rapid progress. Based upon the Moving Picture Experts Group (MPEG) format, satellite and cable broadcast industry also moves towards digital broadcast. 
   Digital broadcast offers several advantages that its analog counterpart cannot provide. For example, digital broadcast is capable of providing services with far more improved video/audio quality, transmitting several different programs within a fixed bandwidth, and offering enhanced compatibility with digital communication media or digital storage media. 
   In digital broadcast, a plurality of programs encoded based upon the MPEG format are multiplexed into a transport stream before transmitted. The transmitted transport stream is received by a set top box at the receiver and demultiplexed into a plurality of programs. If a program is chosen from among the demultiplexed programs, the chosen program is decoded by a decoder in the set top box and original audio and video signals are retrieved. The retrieved audio and video signals can be presented by an A/V output apparatus such as a TV. 
   It is also possible to store the received digital broadcast signals on a storage medium instead of directly outputting the received broadcast signals to A/V output devices. The stored digital broadcast signals can be edited and retrieved afterwards. For example, a digital data stream received by a set top box can be stored in a streamer such as a digital video disk (DVD) recorder through communication interfaces like an IEEE-1394 serial bus. Later, the stored digital data stream can be edited and transmitted back to the set top box so that the original digital audio and video data can be presented. 
   When a received digital data stream is recorded on a recording medium, management information regarding the digital data stream needs to be created and recorded on the recording medium. A conventional method for creating the management information will now be explained with reference to  FIGS. 1 and 2 . 
   If a user&#39;s request for recording an incoming data stream tuned by a tuning unit  110  has been received, a control unit  140  of a set top box  100  informs a control unit  250  of a streamer  200  that a recording mode is set and begins to transfer the received digital stream to the streamer  200  through an IEEE-1394 interface. The control unit  250  of the streamer  200  controls a stream recording unit  220  to record the received data stream on a recording medium  230 . The transport stream packets (TS Pkt  1 ˜TS Pkt k) constituting the data stream are recorded on the recording medium  230  along with respective transport stream packet arrival times (TS APATs), wherein the transport stream packets with packet, arrival times are organized in sectors on the recording medium  230 . 
   When recording the digital stream, the control unit  250  of the streamer  200  groups the transport stream packets into stream object units (SOBU  1 ˜SOBU q), with each stream object unit (SOBU) having a predetermined time length, for example, 0.5 s. The control unit  250  also creates a stream object unit size (SOBU_SZ) and a stream object unit presentation time (SOBU_TM) for each stream object unit (SOBU) and records the created information as management information for the associated stream object unit (SOBU). The stream object unit size (SOBU_SZ) of a stream object unit (SOBU) is expressed in terms of the number of sectors containing the stream object unit. If 20 stream object units (SOBUs) are created after 10 s elapses, the control unit  250  creates and records a stream object unit index number (SOBU_N) for the 20 stream object units. 
   The control unit  250  of the streamer  200  conducts the aforementioned task until the recording mode terminates, thereby creating a record (RCD) or program (PG). The digital stream recorded by a single recording operation is called a record (RCD) or program (PG). After the recording mode ends, the control unit  250  of the streamer  200  groups the created stream object units (SOBUs) into a stream object (SOB) and groups stream object unit sizes (SOBU_SZs) into a map. The map is recorded on the recording medium  230  as stream object information (SOBI). 
   Subsequently, the control unit  250  of the streamer  200  creates and records a presentation sequence information (Cell) with information linking it to the corresponding record (RCD) or program (PG). 
   If a user enters a search time (HH:MM:SS:FF) in order to search for a specific position on the recording medium  230 , the control unit  250  of the streamer  200  detects a record (RCD) or program (PG) corresponding to the user&#39;s search time (HH:MM:SS:FF) with reference to the creation times (PG 1 _Create_TM, PG 2 _Create_TM, PG 3 _Create_TM) of records (RCD 1 ˜RCD 3 ) or programs (PG 1 ˜PG 3 ). Suppose the detected program is PG 2  shown in  FIG. 2 . Then, the control unit  250  detects a Cell (Cell  2  shown in  FIG. 2 ) corresponding to the user&#39;s search time (HH:MM:SS:FF) with reference to the presentation start time (C 1 _S_TM, C 2 _S_TM, . . . , Cn_S_TM) and presentation end time (C 1 _E_TM, C 2 _E_TM, . . . , Cn_E_TM) of each Cell contained in the detected program PG 2 . 
   Referring to the stream object information (SOBI) of the stream object SOB 2  associated with the detected presentation sequence information Cell  2 , the control unit  250  subtracts the stream object start time (SOB_S_TM) from the user&#39;s search time (HH:MM:SS:FF) The control unit  250  searches for a stream object unit (SOBU) based upon the size accumulated up to the stream object unit (SOBU) in which the presentation time accumulated up to the stream object unit (SOBU) is closest to the subtraction result without exceeding it. 
   Suppose that the stream object unit detected by the above-mentioned procedure is SOBUg shown in  FIG. 2 . As the next step, the control unit  250  detects the transport stream packet arrival time (TS APAT) of each transport stream packet from the first sector Sector  1  containing the detected stream object unit SOBUg and compares the packet arrival time with the user&#39;s search time (HH:MM:SS:FF). The control unit  250  starts to retrieve recorded data from the transport stream packet whose packet arrival time is after the user&#39;s search time and controls a stream reproducing unit  240  so that the retrieved data can be transferred to the set top box  100  through the IEEE-1394 interface  210 . 
   As explained thus far, each stream object unit created by the conventional data stream recording method has a predetermined time length. Therefore, in the instance where the transport stream packet corresponding to the user&#39;s search time is the last transport stream packet recorded in the last sector (Sector n) of the associated stream object unit (SOBUg) as shown in  FIG. 3 , a significant search time is required to locate the target transport stream packet. This is because it takes time to obtain the packet arrival time of the last transport stream packet recorded in the last sector (Sector n) since the packet arrival time of the first transport stream packet recorded in the first sector (Sector  1 ) has been detected. 
   The required search time can be fairly reduced by decreasing the time length of each stream object unit. In this case, however, the number of stream object units (SOBUs) increases, which inevitably entails increased amount of overall navigation data as the management data regarding stream object units also increases. 
   In addition, since the time length of each stream object unit is fixed, the size of each stream object unit depends on the bit rate of the input data stream. For example, if an input digital data stream has a bit rate of 10 Mbps, the size of a stream object unit (SOBU) amounts to about 5 Mbit and thus the maximum search time required for locating a transport stream packet within a stream object unit (SOBU) is about 500 ms. In contrast, in the case of a data stream with a bit rate of 0.5 Mbps, a stream object unit (SOBU) has a size of 500 Kbit and the maximum search time required for locating a transport stream packet within a stream object unit (SOBU) amounts to about 50 ms. 
   Unless every recorded program or record has the same transfer rate, the size of a stream object unit varies depending on the transfer rate as shown in  FIG. 4 . The maximum search time, therefore, increases in proportion to the size of a stream object unit and transfer rate. Consequently, the search time is dependent upon the transfer rates of data streams in the conventional method, which may result in confusions and problems. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a method and apparatus for creating and recording management information for digital data streams. When recording a received digital transport stream on a recording medium, stream object units are created so that the maximum search time required for locating a specific position within a stream object unit is uniform among recorded stream object units. 
   It is another object of the present invention to provide a method and apparatus for reproducing data from a recording medium using management information stored on the recording medium. 
   It is another object of the present invention to provide a method and apparatus for reproducing data from a recording medium, which overcome the limitations and disadvantages related to conventional reproducing methods and apparatuses. 
   According to one aspect, the present invention provides a method for reproducing data from a recording medium, the recording medium containing therein access time entries and object unit entries associated with object units, the method comprising the steps of: receiving an access time for accessing data from the recording medium; searching for a target entry point based on the access time by using the access time entries; and searching for a target object unit by using the target entry point and the object unit entries. 
   According to one aspect, the present invention provides an apparatus for reproducing data from a recording medium, the recording medium containing therein access time entries and object unit entries associated with object units, the apparatus comprising a combination of elements for receiving an access time for accessing data from the recording medium, for searching for a target entry point based on the access time by using the access time entries, and for searching for a target object unit by using the target entry point and the object unit entries. 
   These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention, illustrate the preferred embodiments of the invention, and together with the description, serve to explain the principles of the present invention. 
     In the drawings: 
       FIG. 1  is a block diagram of an apparatus in which the present invention can be advantageously employed; 
       FIG. 2  is a pictorial representation showing the syntax of the recorded data and the management information regarding the recorded data for explaining a conventional method for creating management information for data streams recorded on a recording medium and searching for recorded data using the management information; 
       FIG. 3  is a pictorial representation for explaining the problems of the conventional method shown in  FIG. 2 ; 
       FIG. 4  is a pictorial representation showing the size of a stream object unit created by the conventional method; 
       FIG. 5  is a pictorial representation showing the syntax of the recorded data and the management information regarding the recorded data created by the present invention; and 
       FIG. 6  is a pictorial representation showing the size of a stream object unit created by the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In order that the invention may be fully understood, preferred embodiments thereof will now be described with reference to the accompanying drawings. 
     FIG. 1  depicts a block diagram of an apparatus in which the present invention may be advantageously employed. The apparatus comprises a set top box  100 , a communication interface (IEEE-1394), and a streamer  200 , all operatively coupled. 
   The set top box  100  receives transport streams encoded by system encoders and broadcast by a plurality of broadcast stations and demultiplexes the received transport streams. After a decoder  120  decodes the transport stream of a program tuned by a tuning unit  110 , a control unit  140  outputs the decoded transport stream to an A/V output apparatus or to the streamer  200  through the IEEE-1394 communication interface for recording the transport stream. 
   In the set top box  100 , the program service information (SI) contained in the transport stream of the program tuned by the tuning unit  110  is decoded by the decoder  120  and transmitted to the control unit  140 . The control unit  140  stores the program service information (SI) in the program information area (M 1 ) of a memory  150 . The program service information (SI) includes information on all programs of every received channel, such as channel numbers, channel names, program names, schedules, program categories, attributes of streams constituting each program, etc. 
   The control unit  140  may constitute a program table having a time axis and a channel axis using the program service information (SI) stored in the program information area M 1  of the memory  150  and display the program table on a television screen. 
   The set top box  100  may transmit a program chosen by a user through the IEEE-1394 interface to the streamer  200  so that the transmitted program is recorded on a recording medium  230  such as a digital video disk (DVD) by the streamer  200 . 
   In addition, requested by a user, the set top box  100  may receive a program retrieved from the recording medium  230  by the streamer  200  through the IEEE-1394 communication interface so that the received program can be presented on a television after being decoded by the decoder  120 . 
   The method for creating and recording management information for a digital data stream in accordance with an embodiment of the present invention will now be explained with reference to  FIGS. 1 and 5 . 
   If a user&#39;s request for recording an incoming data stream tuned by the tuning unit  110  shown in  FIG. 1  has been received, the control unit  140  of the set top box  100  informs a control unit  250  of the streamer  200  that a recording mode is set and begins to transfer the received digital stream to the streamer  200  through an IEEE-1394 interface. The control unit  140  of the set top box  100  detects the bit transfer rate of the received data stream and transfers the detected bit transfer rate to the streamer  200 , wherein the bit transfer rate can be obtained by detecting the elementary stream rate (ES rate) contained in the header of each packetized elementary stream packet (PES packet) or the piecewise rate (PW rate) contained in the header of each transport stream packet. 
   The control unit  250  of the streamer  200  controls a stream recording unit  220  so that the data stream received through the IEEE-1394 interface can be recorded on the recording medium  230 . The transport stream packets (TS pkt  1 ˜TS pkt k) constituting the data stream are organized in sectors (Sector  1 ˜Sector n) on the recording medium  230  along with respective packet arrival times expressed in terms of internal clock values. The control unit  250  of the streamer  200  varies the time length of a stream object unit (SOBU) depending upon the bit transfer rate of the received data stream transmitted by the set top box  100 . 
   First, the minimum time length of a stream object unit (SOBU), the upper threshold value of the transfer rate (Upper_Th_Rate), and the lower threshold value of the transfer rate (Lower_Th_Rate) are determined. Suppose that the minimum time length, the upper threshold value, and the lower threshold value are set to 0.1 s, 7 Mbps, and 4 Mbps, respectively. If the transfer rate of a data stream (S_RATE) is equal to or greater than the upper threshold rate (Upper_Th_Rate), the data stream is classified into Type  1  and the minimum time length 0.1 s is assigned as the time length of a stream object unit (SOBU) associated with the data stream. If the transfer rate of a data stream (S_RATE) is less than upper threshold rate (Upper_Th_Rate) but greater than the lower threshold rate (Lower_Th_Rate), the data stream is classified into Type  2 . The stream object unit (SOBU) associated with the data streams belonging to Type  2  has a time length of 0.2 s which is the minimum time length 0.1 s multiplied by a predetermined weighting factor 2. Data streams which do not belong to either Type  1  or Type  2  are classified into Type  3  and the stream object unit (SOBU) associated with data streams of Type  3  has a time length of 0.3 s which is the minimum time length 0.1 s multiplied by a predetermined weighting factor 3. It is desirable to record the time length of a stream object unit (SOBU) in the stream object information (SOBI) area because the transfer rate of a program remains unchanged and therefore every stream object unit (SOBU) belonging to a stream object (SOB) has the same time length. 
   The minimum time length of a stream object unit (SOBU) 0.1 s, the upper threshold rate 7 Mbps, the lower threshold rate 4 Mbps, and the weighting values 2 and 3 mentioned before are simply illustrative values and thus can be set differently. Likewise, it is also possible to increase or decrease the number of data stream groups and assign an appropriate weighting factor to each data stream group though digital data streams are classified into three groups depending on their transfer rates in the previous example. 
   With reference to the time information contained in the transport stream packet such as the program clock reference (PCR), packet arrival time (PAT), or presentation time stamp (PTS), the control unit  250  of the streamer  200  records the received data stream as a series of stream object units (SOBU  1 ˜SOBU q), each stream object unit having a time length determined by the transfer rate of the received data stream. In addition, the stream object unit size (SOBU_SZ) of a stream object unit expressed in terms of the number of sectors containing the stream object unit is created. As a result, the stream object unit size (SOBU_SZ) and the stream object unit presentation time (SOBU_TM) for each SOBU, which are also referred to herein as object unit entries, are recorded on the medium  230  as management information of the stream object units (SOBUs). If a predetermined number, for example 20, of stream object units are created while repeating the above task, the control unit  250  creates and records access time entries which include a stream object unit index number (SOBU_N), an accumulated presentation time (ACC_TM), and an accumulated size (ACC_SZ) for the 20 stream object units. The accumulated presentation time (ACC_TM) and accumulated size (ACC_SZ) for each of 20 stream object units are the presentation time and size accumulated from the start position (SOB#n_OFF_ADDR) of the stream object (SOB#n) containing the associated stream object units to each of 20 stream object units, respectively. 
   The control unit  250  of the streamer  200  performs the aforementioned operation until the recording mode terminates, thereby creating a record (RCD) or program (PG). After the recording mode ends, the control unit  250  of the streamer  200  groups the recorded stream object units (SOBUs) into a stream object (SOB) and groups the recorded accumulated sizes (ACC_SZs), the recorded accumulated presentation times (ACC_TMs) and the created stream object unit sizes (SOBU_SZs) into a map. The map is recorded as stream object information (SOBI). 
   Subsequently, the control unit  250  of the streamer  200  creates a presentation sequence information (Cell) for the map and records it as the cell information corresponding to the record or program. 
   Let us consider the size of a stream object unit (SOBU) recorded by the embodiment of the present invention. Suppose that as shown in  FIG. 6  the programs PG  1 , PG  2 , PG  3 , and PG  4  have transfer rates of 6 Mbps, 3 Mbps, 4 Mbps, and 6 Mbps, respectively. Also, suppose that the weighting factors are set to 1.5 and 2 and the upper threshold rate (Upper_Th_Rate) and lower threshold rate (Lower_Th_Rate) are set to 6 Mbps and 3 Mbps, respectively. 
   Since the transfer rate (S_RATE) of the program PG  1  or RCD  1  is equal to the upper threshold rate 6 Mbps, the program PG  1  is classified into Type  1 . Assume that the time length of each stream object unit (SOBU) of the program PG  1  is set to P s and the size of each stream object unit (SOBU) amounts to S Mbit. Since the transfer rate (S_RATE) of the program PG  2  or RCD  2  is equal to the lower threshold rate 3 Mbps, the program PG  2  is classified into Type  3 . In this case, the time length of each stream object unit (SOBU) of the program PG  2  is 2 P s and the size of each stream object unit is S Mbit. Likewise, the program PG  3  is classified into Type  2 . Therefore, the time length of each stream object unit (SOBU) of the program PG  3  is 1.5 P s and the size of each stream object unit is S Mbit. 
   As seen from  FIG. 6 , the size of each stream object unit (SOBU) remains identical without regard to the transfer rates of input data streams, thereby guaranteeing the maximum search time required for locating a transport stream packet within a stream object unit (SOBU) to be uniform. 
   If a user enters a search time (HH:MM:SS:FF) in order to search for a specific position on the recording medium  230 , the control unit  250  of the streamer  200  detects a record (RCD) or program (PG) corresponding to the user&#39;s search time (HH:MM:SS:FF) with reference to the creation times (PG 1 _Create_TM, PG 2 _Create_TM, PG 3 _Creat_TM) of records (RCD 1 ˜RCD 3 ) or programs (PG 1 ˜PG 3 ). Suppose the detected program is PG 2  shown in  FIG. 5 . Then, the control unit  250  detects a Cell (Cell  2  shown in  FIG. 5 ) corresponding to the user&#39;s search time (HH:MM:SS:FF) with reference to the presentation start time (C 1 _S_TM, C 2 _S_TM, . . . , Cn_S_TM) and presentation end time (C 1 _E_TM, C 2 _E_TM, . . . , Cn_E_TM) of each Cell contained in the detected program PG 2 . After obtaining the time length of a stream object unit (SOBU) from the stream object information (SOBI) concerning the stream object SOB  2  associated with the detected cell Cell  2 , the control unit  250  multiplies the stream object unit index number (SOBU_N) by the obtained time length. The control unit  250  searches for an accumulated entry (ACC Entry: the entry to access, which is gray-marked in  FIG. 5 ) containing the stream object index number (SOBU_N) in which the multiplication result is closest to the difference between the user&#39;s search time (HH:MM:SS:FF) and the stream object start time (SOB_S_TM) without exceeding it. Next, the control unit  250  searches for a target stream object unit (SOBU) containing the user&#39;s search time by multiplying the time length of a stream object by the number of stream object units counted from the stream object unit pointed to by the detected accumulated entry (ACC Entry). The position of the target stream object unit (SOBU) can be obtained by adding the accumulated size (ACC_SZ) of the target accumulated entry (ACC Entry) to the sum of stream object sizes (SOBU_SZs) calculated from the stream object unit pointed to by the target accumulated entry (ACC Entry). 
   Suppose that the stream object unit detected by the above-mentioned procedure is SOBUg shown in  FIG. 5 . As the next step, the control unit  250  detects the transport stream packet arrival time (TS APAT) of each transport stream packet from the first sector Sector  1  containing the detected stream object unit SOBUg and compares the packet arrival time with the user&#39;s search time (HH:MM:SS:FF). The control unit  250  starts to retrieve recorded data from the transport stream packet whose packet arrival time is after the user&#39;s search time and controls a stream reproducing unit  240  so that the retrieved data can be transferred to the set top box  100  through the IEEE-1394 interface  210 . 
   The invention may be embodied in other specific forms. For example, the invention is not only applicable to the apparatus shown in  FIG. 1  but applicable to any system comprising a subsystem functioning as a set top box, another subsystem functioning as streamer, and a communication interface between the two systems. 
   In the previous embodiment, the set top box detected the bit rate of a data stream and transmits the detected value to the streamer. It is also possible, however, for the streamer to calculate the bit rate by detecting the elementary stream rate (ES rate) contained in the header of each packetized elementary stream packet (PES packet) or the piecewise rate (PW rate) contained in the header of each transport stream packet after scrambling and decoding the input data stream. 
   Instead of calculating the bit rate of a data stream from the ES rate or PW rate, the data transfer rate information such as the ES rate or PW rate can be used directly. Also, the bit rate can be calculated from the amount of data between two consecutive program clock references (PCRs) contained in the data stream, wherein the bit rate is given as [the data amount (in bytes)×system clock frequency]/[PCR j−PCR i]. 
   In the previous embodiment, it was assumed that the bit rate of a program remained unchanged throughout the program. The present invention is still applicable to data streams in which the upper and lower limits of the bit rate of the data stream are given. 
   The invention may be embodied in other specific forms without departing from the sprit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.