Abstract:
A picture signal reproducing apparatus for synchronously reproducing a variety of digital coded data strings, comprises: data transmission controlling unit for inputting a series of digital multiplexed coded data strings including a plurality of packs connected with each other in serial, each of the packs having a SCR, and inserting a reproduction unit switching information at a seamless point between two packs in the series of digital multiplexed coded data strings according to the SCR for each of the packs; and reproduction controlling unit for detecting the seamless point on the basis of the reproduction unit switching information from the series of digital multiplexed coded data strings to synchronously reproduce the variety of digital coded data strings at the detected seamless point.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for and a method of reproducing a picture signal, and more particularly, to an apparatus for and a method of synchronously reproducing a variety of bit streams, such as audio, video and sub-picture, each having the different system clock reference. The audio, video and sub-picture signals are digital encoded according to a typical coding technology, such as the international standard, ISO-IEC 13818-2, commonly called “MPEG (Moving Picture Expert Group)” and multiplexed to generate a series of digital multiplexed coded bit streams. 
   2. Description of the Related Art 
   Recently, a wide variety of digital storage media rapidly become popular. Such digital storage media is typically a mass storage optical memory disk, such as DVD (Digital Versatile Disk) and adapted to record thereon a multiplexed and digital encoded data including a video signal, an audio signal and an additional information signal, such as a subtitle. 
   In the digital storage media, the video signal is typically encoded according to the MPEG, while the audio signal may be often encoded according to the other standards. The encoded audio and video data may be multiplexed according to a system standard regulated in the MPEG. 
   Referring to  FIG. 4  of the drawings, there is shown an example of the conventional DVD system for reproducing the coded data recorded in the DVD as a picture signal reproducing apparatus  1 . As shown in  FIG. 4 , the picture signal reproducing apparatus  1  is connected to a multiplexed coded stream supplying unit  3 , such as a DVD disk drive, and comprises a data transmission controlling unit  5  and a reproduction controlling unit  7 . The transmission controlling unit  5  is adapted to transmit the coded data recorded in the DVD from the multiplexed coded stream supplying unit  3 . The reproduction controlling unit  7  is adapted to decode the transmitted coded data. 
   The picture signal reproducing apparatus  1  is linked with an external host computer  9  through a host bus  11 . The host computer  9  is adapted to control the data transmission controlling unit  5  and the reproduction controlling unit  7 . The host computer  9  has a file system for the DVD disk and its management information. In accordance with this management information transmitted from the host computer  9 , the data transmission controlling unit  5  is operated to transmit the coded data from the multiplexed coded stream supplying unit  3  to the reproduction controlling unit  7 . The reproduction controlling unit  7  is then operated to decode the coded data on the basis of the coded data transmitted from the data transmission controlling unit  5 . 
   Referring to  FIG. 5  of the drawings, there is shown an example of the structure of the digital multiplexed coded streams according to the DVD video standard in the DVD forum. As shown in  FIG. 5 , the digital multiplexed coded stream includes at least one video object, referred to as “VOB”. Each VOB further includes at least one video object unit, referred to as “VOBU”. Each VOBU further includes a first navigation signal NP and a plurality of video signals VP, audio signals AP, and sub-picture signals SP after the navigation signal NP. Each of the audio, video and sub-picture signals is digital encoded by the encoder, not shown, and then multiplexed for each packet by the multiplexing apparatus, not shown. The digital multiplexed coded streams thus has a series of digital coded data strings including a diversity of information as the audio, video, sub-picture, and so on are multiplexed in order. 
   Referring to  FIG. 6  of the drawings, there is shown an example of the structure of pack and packet as an elementary unit in the typical digital multiplexed coded stream. As shown in  FIG. 6 , the digital multiplexed coded stream has a plurality of packs  13 . Each of packs  13  has a first pack header  14   a  and at least one packet  14   b  after the pack header  14   a . The pack header  14   a  includes a system clock reference, hereinlater referred to as simply “SCR”, having information used for regenerating a system time clock, hereinlater referred to as simply “STC”, to decode the multiplexed stream. 
   Each of packets  14   b  includes a top packet header  15   a  and a coded data  15   b  followed by the packet header  15   a . The packet header  15   a  has a top of synchronous signal  16   a , an identifying code  16   b , referred to as “stream ID” in the drawings, for identifying a variety of packets, such as video, audio and sub-picture, packet length information  16   c , a presentation time stamp  16   d , hereinlater referred to as simply “PTS”, and so on. The PTS  16   d  is indicated when each of reproduction units, i.e., each of packs  13  of the video, audio, and sub-picture is decoded in the reference time and when the coded data  15   b  is reproduced. The coded data  15   b  is that video, audio and sub-picture information are coded by the coding apparatus, and contained in that packet  14   b  corresponding to its stream ID  16   b.    
   In such DVD system, the reproduction order and synchronous reproduction of the video, audio and sub-picture are controlled in accordance with the SCR and the PIS. In the forward reproduction, the SCR monotonously increases. The SCR sometimes decreases at a connection point between particular two continuous packs, because of the fact that particular stream for the DVD video recording can be edited and rearranged. The DVD forum works out “DVD Specification for Rewritable/Re-recordable Discs. Part3 VIDEO RECORDING” version 1.0 issued on September, 1999, as a particular standard for achieving the video recording in the rewritable types of DVD, such as a DVD-RAM. 
   Such connection point between two packs having the different SCR is hereinlater referred to as “seamless point”. The seamless point should accurately be detected in order to reset the synchronization of the video, audio and sub-picture at the seamless point. 
   The host computer  9  can notice the seamless point according to only data stored in the disk. Furthermore, there is another method of detecting the seamless point comprising the steps of: preparing the above information on the seamless point of the host computer  9 ; decoding the coded stream by the reproduction controlling unit  7  to derive the SCR; and matching the prepared information on the seamless point with the derived SCR to detect the actual seamless point. 
   Referring to  FIG. 7  of the drawings, there is shown a graph of an example of the variation in the SCR between two video object units VOBU 0  and VOBU 1 . As shown in  FIG. 7 , the SCR of the first video object unit VOBU 0  gradually increases at first. After the seamless point, the SCR of the next video object unit VOBU 1  may be assumed to be four patterns of variation. 
   In the patterns of variation on the lines A and B in  FIG. 7 , the SCR falls down at the seamless point and thereafter gradually rises. In the pattern of variation on the line C, the SCR constantly increases before and after the seamless point. In the pattern of variation on the line D, the SCR rises up at the seamless point and thereafter further gradually rises. 
   In the aforesaid patterns of variation on the lines A and B, the seamless point can be detected on the basis of the SCR contained in the top of the navigation pack NP for each video object unit VOBU. It is however impossible to detect the seamless point on the basis of these SCR in the aforesaid patterns of variation on the lines C and D. The above variations in the SCR on the lines C and D may occur when the streams are edited and rearranged. 
   In Japanese Non-examines Patent Publication No. H10-26221 there is disclosed a typical method of reproducing the picture signal on the basis of the seamless point detected according to the SCR in which the picture signal reproducing apparatus may be controlled in accordance with the difference between the last SCR of the former pack and the top SCR of the latter pack. This method may be constructed on the assumption that the top SCR of the latter pack should be smaller than the last SCR of the former pack. For this reason, the seamless point cannot be detected in case of the aforesaid pattern of variation in the SCR on the line D. 
   According to the DVD Specification for Rewritable/Re-recordable Discs. Part3 VIDEO RECORDING, it is assumed that the last SCR of the pack before the seamless point and the top SCR of the pack after the seamless point may be defined as management information and the seamless point may be detected on the basis of predetermined system clock references for both of the aforesaid packs in the picture signal reproducing apparatus. 
   The above conventional picture signal reproducing apparatus  1 , however, should be operated to transmit the information on the SCR monitored by the host computer  9  for each reproduction unit to the picture signal reproducing apparatus  1  when the stream is transmitted from a prior input buffer, such as the multiplexed coded stream supplying unit  3 , to the picture signal reproducing apparatus  1 . This process is troublesome in the management. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a picture signal reproducing apparatus for synchronously reproducing a variety of digital coded data strings having a plurality of reproduction units connected in serial which it is possible to detect a connection point between the reproduction units without fail. 
   It is another object of the present invention to provide a picture signal reproducing method of synchronously reproducing a variety of digital coded data strings having a plurality of reproduction units connected in serial which it is possible to detect a connection point between the reproduction units without fail. 
   In accordance with a first aspect of the present invention, there is provided a picture signal reproducing apparatus for synchronously reproducing a variety of digital coded data strings, comprising: data transmission controlling means for inputting a series of digital multiplexed coded data strings including a plurality of reproduction units connected with each other in serial, each of the reproduction units having a system clock reference, and inserting a reproduction unit switching information at a connection point between two reproduction units in the series of digital multiplexed coded data strings according to the system clock reference for each of the reproduction units; and reproducing means for detecting the connection point on the basis of the reproduction unit switching information from the series of digital multiplexed coded data strings to synchronously reproduce the variety of digital coded data strings at the detected connection point. 
   Here, the above variety of digital coded data strings means each of packets which is generated by the encoding apparatus by encoding audio, video, sub-picture and so on. The each of packets, such of audio, video and sub-picture packets, has different reproduction clocks. A plurality of the packets gather together into a reproduction unit, a pack, having a system clock reference for synchronizing variety of packets one another. The packs are connected with each other to obtain a series of digital multiplexed coded data strings, i.e., multiplexed coded streams. The reproduction unit switching information is contained in a seamless packet and inserted into the seamless point of the multiplexed coded streams. 
   In the aforesaid apparatus, the data transmission controlling means may have: a connection point detecting unit for detecting the connection point between the reproduction units; a switching information producing unit for producing the reproduction unit switching information; and a switching information inserting unit for inserting the reproduction unit switching information at the connection point between the reproduction units in the series of digital multiplexed coded data strings. 
   In the aforesaid apparatus, each of the reproduction units may have a header including the reproduction unit switching information. Furthermore, the reproducing means may have: a header analyzing unit for analyzing to detect the connection point between the reproduction units on the basis of the reproduction unit switching information; and a decoding unit for decoding the series of digital multiplexed coded data strings to synchronously reproduce the variety of the digital coded data strings according to the detected reproduction unit switching information. 
   In the aforesaid apparatus, the reproduction unit switching information produced by the switching information producing unit of the data transmission controlling means may include a first system clock reference of the reproduction unit just before the connection point and a second system clock reference of the reproduction unit just after the connection point. 
   In the aforesaid apparatus, said reproduction unit switching information produced by said switching information producing unit of said data transmission controlling means may include an identifying code, and said header analyzing unit of said reproducing means being operated to analyze said identifying code to detect said switching information. 
   In accordance with a second aspect of the present invention, there is provided a picture signal reproducing method of synchronously reproducing a variety of digital coded data strings, comprising the steps of:
     (a) inputting a series of digital multiplexed coded data strings including a plurality of reproduction units connected with each other in serial, each of the reproduction units having a system clock reference;   (b) inserting a reproduction unit switching information at a connection point between two reproduction units in the series of digital multiplexed coded data strings according to the system clock reference for each of the reproduction units;   (c) detecting the connection point on the basis of the reproduction unit switching information from the series of digital multiplexed coded data strings; and   (d) synchronously reproducing the variety of digital coded data strings at the detected connection point.   

   In the aforesaid method, the reproduction unit switching information may include a first system clock reference of the reproduction unit just before the connection point and a second system clock reference of the reproduction unit just after the connection point. 
   In the aforesaid method, the reproduction unit switching information produced in the step (b) may include an identifying code, and the step (c) having the step of analyzing the identifying code to detect the switching information. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention and many of the advantages thereof will be better understood from the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  is a schematic block diagram of a preferred embodiment of the picture signal reproducing apparatus according to the present invention; 
       FIG. 2  is a schematic diagram of an example of the structure of the seamless packet inserted by the picture signal reproducing apparatus shown in  FIG. 1 ; 
       FIG. 3  is a flowchart showing an example of the flow of the seamless point detecting process in the header analyzing unit of the picture signal reproducing apparatus as shown in  FIG. 1 ; 
       FIG. 4  is a schematic block diagram of an example of the conventional apparatus for reproducing the picture signal; 
       FIG. 5  is a schematic diagram of an example of the structure of pack and packet in the typical multiplexed coded streams according to the DVD video standard; 
       FIG. 6  is a schematic diagram of an example of the structure in the typical multiplexed coded stream; and 
       FIG. 7  is a graph showing the characteristics of the variation in the SCR before and after the seamless point. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Throughout the following detailed description, similar reference characters refer to similar elements in all figures of the drawings. 
   Referring now to  FIG. 1  of the drawings, there is shown a preferred embodiment of the picture signal reproducing apparatus  20  according to the present invention. As shown in  FIG. 1 , the picture signal reproducing apparatus  20  is linked with an external hose computer  9  through a host bus  11 , and comprises a transmission controlling unit  21  and a reproduction controlling unit  23 . The picture signal reproducing apparatus  20  is also connected to a multiplexed coded stream supplying unit  3 . The picture signal reproducing apparatus  20  thus constructed is designed to input, through the multiplexed coded stream supplying unit  3 , a bit stream which is previously obtained by digital encoding video, audio, sub-picture signals and so on, and multiplexing the digital encoded signals for each packet unit, and to then synchronously reproduce the video, audio and sub-picture signals with one another. 
   The data transmission controlling unit  21  includes a connection point detecting unit  25 , a switching information producing unit  27  and a switch  29 . The data transmission controlling unit  21  is adapted to insert a seamless packet at the seamless point in the multiplexed bit streams. 
   The connection point detecting unit  25  is connected to the host computer  9  through the host bus  11  and designed to input a first signal SIG 1  from the host computer  9  through the host bus  11 . The first signal SIG includes reproduction unit management information. The connection point detecting unit  25  is further designed to derive the reproduction unit management information from the first signal SIG 1  and then to detect a seamless point on the basis of the derived reproduction unit management information. The above reproduction unit management information including information on the system clock reference for each reproduction unit can be obtained by the hose computer  9  on the basis of the information contained in the navigation information in the multiplexed coded streams. The reproduction unit management information, hereinlater referred to as “seamless point information”, includes a system clock reference of the reproduction unit just before the seamless point and a system clock reference of the reproduction unit just after the seamless point. 
   The connection point detecting unit  25  is further connected to the multiplexed coded stream supplying unit  3  and designed to input the streams from the multiplexed coded stream supplying unit  3  and then to analyze the inputted streams to detect the seamless point. According to the analysis result, the connection point detecting unit  25  is operated to perform a normal process for the packets just before the seamless point. On the other hand, the connection point detecting unit  25  is operated to output the second signal SIG  2  including the seamless point information to the switching information producing unit  27  in response to the detection of the seamless point. 
   The switching information producing unit  27  is connected to the connection point detecting unit  25  and designed to input a second signal SIG 2  including the seamless point information from the connection point detecting unit  25 . In response to the input of the second signal SIG 2 , the switching information producing unit  27  is activated. After the activation, the switching information producing unit  27  is further designed to produce reproduction unit switching information on the basis of the seamless point information, i.e., a seamless packet, and to then output the produced seamless packet and a third signal SIG 3  to the switch  29 . In response to this third signal SIG 3 , the switch  29  is operated to select the seamless packet transmitted from the switching information producing unit  27  to be transmitted to the reproduction controlling unit  23 . Therefore, the seamless packet can be inserted at the seamless point in the multiplexed coded streams. 
   The switch  29  has a first and second input terminals IN 1  and IN 2  and an output terminal OUT. The switch  29  is connected to the connection point detecting unit  25  through the first input terminal IN 1  and connected to the switching information producing unit  27  through the second input terminal IN 2 . 
   The switch  29  is designed to input the streams from the connection point detecting unit  25  and input the seamless packet and the third signal SIG 3  from the switching information producing unit  27  and then select either one of the streams or the seamless packet to be outputted through the output terminal OUT in accordance with the third signal SIG 3 . More specifically, in response to the input of the third signal SIG 3 , the switch  29  is operated to select the seamless packet inputted through the second input terminal IN 2  to be outputted through the output terminal OUT. On the other hand, when the third signal SIG 3  is not inputted, i.e., in the normal mode, the switch  29  is operated to select the streams inputted through the first input terminal IN 1  to be outputted through the output terminal OUT. The operation of the switch  29  thus achieves the insertion of the seamless packet at the seamless point in the multiplexed coded streams. 
   The reproduction controlling unit  23  includes a header analyzing unit  31  and a decoding unit  33  as shown in FIG.  1  and is designed to detect the seamless packet from the streams transmitted from the transmission controlling unit  21  to determine the seamless point in the multiplexed coded streams and then to decode the multiplexed coded streams. 
   The header analyzing unit  31  is connected to the switch  29  of the transmission controlling unit  21  and designed to input the multiplexed coded streams including the seamless packet to analyze the header in each packet in the inputted streams and then to output a coded data and a fourth signal SIG 4  having analysis result information on the results of the analysis of the header. 
   The decoding unit  33  is connected to the header analyzing unit  31  and designed to input the coded data and the fourth signal SIG 4  from the header analyzing unit  31  to reproduce the inputted coded data on the basis of the analysis result information in the inputted fourth signal SIG 4  and then to output the video, audio and sub-picture to outside. 
   Referring to  FIG. 2  of the drawings, there is shown an example of the structure and the insertion position of the seamless packet generated by the switching information producing unit  27  in this embodiment. In this embodiment, the seamless packet includes a packet header  40  having a synchronous signal  41 , an identifying code  42 , and a packet length signal  43 , first and second system clock reference signals  44  and  45  after the packet header  40 . 
   The identifying code  42  is the streams ID and used for the judgment of the seamless packet. In this embodiment, the streams ID contained in the seamless packet may be previously assigned to any IDs except for the streams ID used for the normal streams conformable to the DVD. The first system clock reference signal  44  is the SCR of the pack P 0  just before the seamless point, while the second system clock reference signal  45  is the SCR of the pack P 1  just after the seamless point. Both of the first and second system clock reference signals  44  and  45  are obtained from the seamless point information in the second signal SIG 2 . The first and second system clock reference signals  44  and  45  are used for preventing a failure in detecting the seamless packet when an error occurs in the streams. The error in the streams can be therefore detected by comparing the SCR of the pack P 0  before the seamless point with the SCR of the pack P 1  after the seamless point. 
   Referring now to  FIG. 3  of the drawings, there is shown a flowchart of the flow of a process of detecting the seamless point in the header analyzing unit  31  of the picture signal reproducing apparatus  20  according to the present invention. As shown in  FIG. 3 , the seamless point detecting process comprises steps ST 1  to ST 7 . 
   In the step ST 1 , the header analyzing unit  31  is operated to start to analyze the pack and the packet in response to the detections of the pack header and the packet header, respectively. In the following step ST 2 , the header analyzing unit  31  is operated to derive the stream ID from the packet header. In the step ST 3 , the header analyzing unit  31  is then operated to judge whether the obtained stream ID is indicative of the seamless packet or not. When the stream ID is indicative of the seamless packet, the analyzed target packet is judged to be the seamless packet. The step ST 3  then goes to the step ST 5 . When the obtained stream ID is indicative of any one except for the seamless packet, the analyzed target packet is judged to the packets of the video, audio and sub-picture, and then the step ST 3  goes to the step ST 4 . In the step ST 4 , the coded data in the target packet is judged to be effective and therefore transmitted to the decoding unit  33 , while this process is then terminated. 
   On the other hand, even when the judgment in the step ST 3  is made that the stream ID in the target packet is indicative of the seamless packet, the stream ID sometime becomes unexpectedly the same stream ID of the seamless packet due to an error in the streams. The judgment process in the following step ST 5  can prevent such unfortunate mistake in the detection of the seamless packet. 
   In the step ST 5 , the internal information in the packet identified as the seamless packet in the step ST 3  is compared with the SCR of the packet P 0  before the seamless packet and the SCR of the packet P 1  after the seamless packet. In this case, the seamless packet may have an internal structure as shown in FIG.  2 . When the first system clock reference signal  44  is identical with the SCR of the packet P 0  before the seamless packet and when the second system clock reference signal  45  is also identical with the SCR of the packet P 1  after the seamless packet, the target packet is defined as the seamless packet. When, on the contrary, either one of the first and second system clock reference signals  44  and  45  is different from the corresponding SCR, the target packet is assumed to make an error. In this case, the header analyzing unit  31  is operated to derive no seamless point. The step ST 5  then goes to the step ST 7 . 
   In the step ST 6 , the header analyzing unit  31  is operated to output the fourth signal SIG 4  including the analysis result information according to the results made in the steps ST 3  and ST 5  to the decoding unit  33  in order to make the decoding unit  33  notice that the target packet is defined as the seamless point. In the step ST 7 , the coded data corresponding to the target packet is discarded. 
   The steps ST 1  to ST 7  in the above process can be repeated for the whole multiplexed encoded streams sequentially. 
   The seamless point detecting process thus constructed can built a relationship between the seamless point and the SCR, thereby making it possible to exactly detect the seamless point. 
   The operation of the picture signal reproducing apparatus  20  of this embodiment will the described hereinlater in detail. 
   Firstly, all processes except for the seamless point detecting process will be described. 
   The switch  29  of the transmission controlling unit  21  is usually operated to select the first input terminal IN 1  to transmit the multiplexed coded streams from the multiplexed coded stream supplying unit  3  through the connection point detecting unit  25  of the transmission controlling unit  21  to the header analyzing unit  31  of the reproduction controlling unit  23  therethrough. The header analyzing unit  31  of the reproduction controlling unit  23  is then operated according to the steps in the header analyzing process shown in FIG.  3 . 
   Firstly, in the step ST 1 , the multiplexed coded streams transmitted from the transmission controlling unit  21  is analyzed by the header analyzing unit  31  to derive the pack header and the packet header from the transmitted multiplexed coded streams. The step ST 1  proceeds to the next step ST 2 , wherein the stream ID is derived from the obtained packet header. In the following step ST 3 , the judgment is made whether the obtained stream ID is indicative of the seamless packet or not. In the case where the obtained stream ID is not indicative of the seamless packet, the step ST 3  proceeds to the step ST 4 , wherein the fourth signal SIG 4  including the coded data and the analysis result information are transmitted to the reproduction controlling unit  23 . 
   In the decoding unit  33  of the reproduction controlling unit  23 , the transmitted coded data is reproduced on the basis of the transmitted analysis result information to then output the video, audio and sub-picture to outside. 
   Next, the seamless point detecting process will be described hereinlater. 
   The seamless point is detected by the connection point detecting unit  25  on the basis of the seamless point information of the reproduction unit management information contained in the first signal SIG 1  inputted from the host computer  9  through the host bus  11 . 
   In the response to the detection of the seamless point in the connection point detecting unit  25 , the seamless point information is contained in the second signal SIG 2  and then transmitted to the switching information producing unit  27 . 
   In response to the second signal SIG 2  including the seamless point information inputted from the connection point detecting unit  25 , the switching information producing unit  27  is activated. The switching information producing unit  27  is then operated to control the switch  29  in accordance with the third signal SIG 3  and to generate the seamless packet on the basis of the seamless point information. The generated seamless packet is then outputted to the switch  29  from the switching information producing unit  27 . The switch  29  is then operated to select the second input terminal IN 2  to input the seamless packet from the switching information producing unit  27  therethrough in response to the third signal SIG 3 . As a result, the seamless packet is transmitted to the header analyzing unit  31  of the reproduction controlling unit  23 . 
   The switching information producing unit  27  is thereafter operated to output the third signal SIG 3  to the switch  29  thereby making the switch  29  select the first input terminal IN 1 . 
   The seamless packet can be therefore inserted at the seamless point in the multiplexed coded streams. The multiplexed coded streams including the seamless packet thus obtained is then processed by the header analyzing unit  31  of the reproduction controlling unit  23  according to the steps in the seamless point detecting process shown in FIG.  3 . 
   Firstly, in the step ST 1 , the multiplexed coded streams transmitted from the transmission controlling unit  21  is analyzed by the header analyzing unit  31  of the reproduction controlling unit  23  to derive the pack header and the packet header from the transmitted multiplexed coded streams. The step ST 1  proceeds to the next step ST 2 , wherein the stream ID is derived from the obtained packet header. 
   In the following step ST 3 , the judgment is made whether the detected stream ID is indicative of the seamless packet or not. In this case, the stream ID is indicative of the seamless packet, the step ST 3  proceeds to the step ST 5 , wherein the internal information in the packet identified as the seamless packet in the step ST 3  is compared with both of the SCR of the packet P 0  before the seamless packet and the SCR of the packet P 1  after the seamless packet. More specifically, the judgment is made whether the first system clock reference signal  44  is identical with the SCR of the packet P 0  before the seamless packet or not, and the judgment is also made whether the second system clock reference signal  45  is also identical with the SCR of the packet P 1  after the seamless packet or not. When both signals are respectively identical with the corresponding SCRS, the step ST 5  goes to the step ST 6  wherein the target packet is definitely defined as the seamless packet. Furthermore, the fourth signal SIG 4  is then outputted from the header analyzing unit  31  of the reproduction controlling unit  23  to make the decoding unit  33  of the header analyzing unit  31  notice the seamless point. In the following step ST 7 , the coded data in the seamless packet is discarded. 
   When, on the other hand, the judgment in the aforesaid step ST 5  that the target packet is not identified as the seamless packet, the step ST 6  is bypassed and the step ST 5  proceeds to the step ST 7  wherein the coded data in the target packet is also discarded. 
   In the decoding unit  33  of the reproduction controlling unit  23 , the video, audio and sub-picture can be therefore synchronously reproduced at the seamless point on the basis of the fourth signal SIG 4  according to the analysis result in the analyzing unit  33 . 
   It will be understood from the foregoing description that the picture signal reproducing apparatus according to the present invention in which the information is transmitted from the external host computer and inserted into the streams, and the seamless point is detected according to this information for reproduction, thereby making it possible to exactly detect the seamless even when the SCR does not fall down at the seamless point as well as even when an error occurs in the streams. 
   Those skilled in the art having the benefit of the teachings of the present invention as hereinabove set forth, can effect numerous modifications thereto. These modifications are to be construed as being encompassed within the scope of the present invention as set forth in the appended claims.