Abstract:
An apparatus and method for implementing a still function of a DVD are provided. According to the apparatus and method of the present invention, a still frame is accurately implemented by detecting a frame to be stilled at a system level and processing it internally without help of any external host computer. In the manner according to the present invention, a still function can be quickly processed and a still frame can be displayed at the exact time required.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a technique for implementing a still function of a DVD, and more particularly to an apparatus and a method for accurately implementing a still function of a DVD. 
   2. Description of the Background Art 
     FIG. 1  is a schematic block diagram of an apparatus for implementing a still function of a DVD in accordance with a conventional art. 
   As shown in the drawing, the apparatus for implementing a still function of a DVD of a conventional art includes a system decoder  2  for receiving a data (VOBU) outputted from a DVD reproducing unit  1 , decoding it to output A/V bit streams (A/V_EL_ST), and extracting presentation time stamps (PTS); a bit stream buffer  3  for receiving the A/V bit streams from the system decoder  2  and buffering it; an A/V decoder  4  for receiving and decoding the A/V bit streams (A/V_EL_ST) from the bit stream buffer  3 , and displaying it according to the presentation time stamps (PTS); and a host computer  5  for receiving an inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST), comparing the inherent number of the A/V bit streams (A/V_EL_ST) with an inherent still frame number (Still_VO_LBN) of a navigation data outputted from the DVD reproducing unit  1 , and controlling the A/V bit streams output of the system decoder  2  according to the comparison result. 
   The operation of the apparatus for implementing a still function of a DVD of the conventional art constructed as described above will now be explained with reference to the accompanying drawings. 
   First, the system decoder  2  receives the data (VOBU) reproduced and outputted from the DVD reproducing unit  1 , decodes the data (VOBU) and stores the A/V bit streams (A/V_EL_ST) in the bit stream buffer  3 . In addition, the system decoder  2  extracts the presentation time stamps (PTS) of each video frame from the data (VOBU) reproduced and outputted from the DVD reproducing unit  1  and transmits it to the A/V decoder  4 . 
   When the A/V bit streams (A/V_EL_ST) stored after being received from the system decoder  2  grows to a size of one frame, the bit stream buffer  3  transmits it to the A/V decoder  4 . 
   Then, the A/V decoder  4  receives the A/V bit streams (A/V_EL_ST) from the bit stream buffer  3 , decodes and restore it into its original A/V data. And the A/V decoder  4  also displays the restored A/V data on a screen according to the presentation time stamps inputted from the system decoder  2 . 
   When the inherent still frame number (Still_VO_LBN) of the navigation data is outputted from the DVD reproducing unit  1 , the host computer  5  compares the inherent still frame number (Still_VO_LBN) with the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) inputted from the system decoder  2 . 
   Upon comparison, if the inherent number (Still_VO_LBN) of the still frame and the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) are identical to each other, the host computer  5  controls the output of the system decoder  2 . Under the control of the host computer  5 , the A/V bit streams (A/V_EL_ST) corresponding to the video frame to be stilled is stored in the bit stream buffer  3 . 
   Thereafter, when the A/V decoder  4  receives the video frame to be stilled from the bit stream buffer  3  and decodes it, the bit stream buffer  3  is turned to an underflow state, according to which the A/V decoder  4  displays the lastly decoded frame. 
   In other word, the apparatus for implementing a still function of a DVD in accordance with the conventional art provides a still frame by utilizing a function of most MPEG decoders that when an underflow occurs in the bit stream buffer  3 , a frame just prior to the underflow is stopped and displayed. 
   Generally, in case of a finite still, a still time is defined between 0˜244 ms. Thus, in order to implement a still function accurately, the time point when a command on the still is inputted from an external source must be accurately recognized. 
   However, in the conventional apparatus for implementing a still function of a DVD by utilizing the underflow of the bit stream buffer, there is a possibility that a frame to be stilled is not stilled due to a delay in the decoding and displaying operation of the A/V decoder. And thus it may cause a problem that a stability of the system is degraded. 
   In addition, in the conventional apparatus for implementing a still function of a DVD, a delay time that data buffered in the bit stream buffer is displayed is different depending on the internal structure of the A/V decoder, Accordingly, it is difficult to detect at what time point the still occurs. 
   Therefore, in order to solve the problem, the conventional apparatus for implementing a still function of a DVD, the periodically reads the presentation time stamp of the video frame being displayed after all A/V bit streams of a frame including still information are applied to the system decoder. And the host computer compares the presentation time stamp extracted by the system decoder with the presentation time stamp of the video frame to be stilled and judges whether the currently displayed video frame is a video frame to be stilled. 
   However, it still has a problem that the A/V decoder should repeatedly perform the comparing operation between the presentation time stamps of the video frame to be stilled and the presentation time stamp of the currently displayed video frame until the frame to be stilled is displayed. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a novel apparatus and method for accurately implementing a still function of a DVD, wherein a frame to be stilled is detected at a system level and internally processed without any help of external host computer, thereby a still function can be quickly processed and a still frame can be displayed at the exact time required. 
   To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an apparatus for implementing a still function of a DVD including: a system decoder for receiving a data outputted from a DVD reproducing unit, decoding it and outputting A/V bit streams; a still detecting unit for detecting an inherent number of the A/V bit streams outputted from the system decoder, comparing it with an inherent number of a still frame outputted from a host computer, and outputting a still detect signal; a still processing unit for receiving the still detect signal from the still detecting unit and outputting a still flag to control a still time point; a bit stream buffer for receiving the A/V bit streams from the system decoder and buffering it; and an A/V decoder for being switched to a still mode by the still flag outputted from the still processing unit, decoding the A/V bit streams read by the bit stream buffer and displaying a still frame. 
   To achieve the above objects, there is also provided a method for implementing a still function of a DVD including the steps of: extracting an inherent number of a still frame and an inherent number of A/V bit streams and storing them; and comparing the inherent number of the still frame and the inherent number of the A/V bit streams, and performing the still function if the inherent number of the still frame and the inherent number of the A/V bit streams are identical. 
   The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     In the drawings: 
       FIG. 1  is a schematic block diagram of an apparatus for implementing a still function of a DVD in accordance with a conventional art; 
       FIG. 2  is a schematic block diagram of an apparatus for implementing a still function of a DVD in accordance with the present invention; and 
       FIG. 3  is a flow chart of a method for implementing a still function of a DVD in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 2  is a schematic block diagram of an apparatus for implementing a still function of a DVD in accordance with the present invention. 
   As shown in the drawing, an apparatus for implementing a still function of a DVD of the present invention includes a DVD reproducing unit  100 , a host computer  200 , a system decoder  300 , a bit stream buffer  400 , a still detecting unit  500 , a still processing unit  600  and an A/V decoder  700 . 
   The still detecting unit  500  includes a first Register  10  for receiving an inherent number (A/V_PCK_LBN) of A/V bit streams (A/V_EL_ST) from the system decoder  300  and storing it; a second Register  20  for receiving an inherent number (Still_VO_LBN) of a still frame from the host computer  200 ; and a first comparator for reading the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) stored in the first Register  10  and the inherent number (Still_VO_LBN) of the still frame stored in the second Register  20 , comparing them, and outputting a still detect signal (Still_DET) if the two numbers are identical to each other upon comparison. 
   The still processing unit  600  includes a third Register  40  for receiving a write request signal (WR_REQ) from the system decoder  300  and outputting a write pointer signal (WR_Pointer); a fourth Register  50  for receiving a write pointer signal (WR_Pointer) at a time point when the still detect signal (Still_DET) is inputted from the still detecting unit  500 , from the third Register  40  and storing it; a fifth Register  70  for receiving a read request signal (RD_REQ) from the A/V decoder  700  and outputting a read pointer signal (RD_Pointer); and a second comparator  60  for receiving the read pointer signal (RD_Pointer) of the fifth Register  70  and the write pointer signal (WR_Pointer) of the fourth Register  50 , comparing them, and setting a still flag  80  if the read pointer signal (RD_Pointer) is equal to or greater than the write pointer signal (WR_Pointer), upon comparison. 
   The apparatus for implementing a still function of a DVD in accordance with the present invention constructed as described above will now be explained with reference to the accompanying drawings. 
   First, the host computer  200  extracts a still frame inherent number (Still_VO_LBN) of a navigation data outputted after being reproduced by the DVD reproducing unit  100  and outputs the extracted still frame inherent number (Still_VO_LBN) to the still detecting unit  500 . 
   The system decoder  300  receives the data (VOBU) reproduced and outputted from the DVD reproducing unit  100 , decodes it and outputs the A/V bit streams (A/V_EL_ST), under the control of the host computer  200 . 
   In addition, in order to store the A/V bit streams (A/V_EL_ST) in the bit stream buffer  400 , the system decoder  300  outputs a write request signal (WR_REQ) to the bit stream buffer  400  whenever the A/V bit streams is outputted by frame, and outputs presentation time stamps (PTS) to display the frame. 
   At this time, the still detecting unit  500  receives the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) from the system decoder  300 , compares the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) with the still frame inherent number (Still VO_LBN) outputted from the host computer  200 , and outputs a still detect signal (Still_DET) if the two numbers are identical to each other upon comparison. 
   That is, the second Register  20  of the still detecting unit  500  stores the still inherent number (Still VO_LBN) outputted from the host computer  200 , and the first Register  10  stores the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) outputted after being decoded by the system decoder  300 . 
   And then, the first comparator  30  compares the inherent number (Still_VO_LBN) of the still frame stored in the second Register  20  and the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/B_EL_ST) stored in the first register  10 , and then, if the two inherent numbers are identical to each other upon comparison, the first comparator  30  outputs the still detect signal (Still_DET). 
   Thereafter, when the still detect signal (Still_DET) is inputted from the first comparator  30  of the still detecting unit  500  to the fourth Register  50  of the still processing unit  600 , the fourth Register  50  stores the write pointer signal (WR_Pointer) outputted from the third Register  40  at the time point of receiving the still detect signal (Still_DET). 
   And, the second comparator  60  compares the write pointer (WR_Pointer) stored in the fourth Register  50  with the read pointer (RD_Pointer) stored in the fifth Register  70 . Upon comparison, if the read pointer (RD_Pointer) is equal to or greater than the address assigned by the write pointer signal (WR_Pointer), the second comparator  60  sets the still flag  80 . 
   Meanwhile, the third Register  40  of the still processing unit  600  receives the write request signal (WR_REQ) from the system decoder  300  and outputs the write pointer (WR_Pointer) of the bit stream buffer  400  at which the A/V bit streams (A/V_EL_ST) is to be written. 
   The fifth Register  70  of the still processing unit  600  receives the read request signal (RD_REQ) from the A/V decoder whenever the AV decoder  700  displays the A/V bit streams by frame, and outputs the read pointer (RD_Pointer) of the bit stream buffer  400  at which the A/V bit streams (A/V_EL_ST) is to be read. 
   The write pointer (WR_Pointer) and the read pointer (RD_Pointer) are sequentially increased by the size of A/V bit stream unit written in or read out from the bit stream buffer  400 . 
   At this time, in the bit stream buffer  400 , the A/V bit streams (A/V_EL_ST) outputted from the system decoder  300  is written in the address region designated by the write pointer signal (WR_Pointer) outputted from the still processing unit  600 , and the A/V bit streams (A/V_EL_ST) written after being inputted from the system decoder  300  is read by the A/V decoder  700  from the address region of the bit stream buffer  400  pointed by the read pointer signal (RD_Pointer) outputted from the still processing unit  600 . 
   At this time, when the still flag  80  inputted from the still processing unit  600  is reset, the A/V decoder  700  decodes the A/V bit streams (A/V_EL_ST) read from the bit stream buffer  400  as a single frame, and outputs the decoded frame according to the presentation time stamps (PTS) inputted from the system decoder  300 , so as to be displayed. 
   Meanwhile, if the still flag  80  inputted from the still processing unit  600  is set, the A/V decoder  700  is switched to a still mode and decodes the A/V bit streams read from the bit stream buffer  400 . 
   And, when the decoded A/V bit streams makes a single frame, the A/V decoder  700  processes it to be still and clears the still flag  80 , and at the same time, it outputs a still interrupt signal (Still_Int) to the host computer  200  to inform of the starting of the video still function. And then, the A/V decoder  700  is switched to a standby mode, waiting for a command from the host computer  200 . 
   After the A/V decoder  700  is switched to a still mode, when a sequence end code (Sequence_End_Code) is detected from the bit stream buffer  400 , the A/V decoder  700  displays repeatedly the frame decoded just prior to detection of the sequence end code, thereby implementing a still function. 
     FIG. 3  is a flow chart of a method for implementing a still function of a DVD in accordance with the present invention. 
   As shown in the drawing, first, the still frame inherent number (Still_VO_LBN) of the DVD and the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) are stored (ST 1 )(ST 2 ), and then the inherent number (Still_VO_LBN) of the still frame and the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) are compared (ST 3 ). 
   Upon comparison, if the inherent number of the still frame (Still_VO_LBN) and the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_L_ST) are not identical to each other, whenever a new A/V bit streams (A/V_EL_ST) is inputted, the comparing operation is repeatedly performed until the inherent number (A/V_PCK_LBN) of the A/V bit streams (A/V_EL_ST) and the inherent number (Still_VO_LBN) of the still frame are identical to each other (ST 4 ). 
   Meanwhile, in case that the inherent number of the still frame (Still_VO_LBN) and the inherent number (A/V_PCK LBN) of the A/V bit streams (A/V_EL_ST) are identical to each other, the write pointer signal (WR_Pointer) for assigning an address of the bit stream buffer  400  in which the A/V bit streams (A/V_EL_ST) are to be written at the time point when the two numbers are identical, is compared with the read pointer signal (RD_Pointer) for assigning an address region of the bit stream buffer  400  whenever the A/V bit streams (A/V_EL_ST) is read (ST 4 ). 
   Upon comparison, in case that the write pointer signal (WR_Pointer) of the bit stream buffer  400  is greater than the read pointer signal (RD_Pointer), the comparing operation is repeatedly performed until the read pointer signal (RD_Pointer) is greater than or the same as the write pointer signal (WR_Pointer), whenever the read pointer signal (RD_Pointer) is changed. (ST 6 ). 
   Meanwhile, if write pointer signal (WR_Pointer) of the bit stream buffer  400  is smaller than or equal to the read pointer signal (RD_Pointer), the still flag  80  is set (ST 5 )(ST 7 ). 
   After the still flag  80  is set, when the sequence end code (Sequence_End_Code) is detected, the frame decoded just before the sequence end code (Sequence_End_Code) is detected is repeatedly displayed, thereby implementing a still function (ST 8 )(ST 9 ). 
   As so far described, according the apparatus and method for implementing a still function of a DVD of the present invention, when a frame processed to be stilled is detected, the write pointer signal of the bit stream buffer at the time of detection of the still frame is stored. 
   And then, whenever the bit buffer is read, the write pointer signal is compared with the read pointer signal, so that when the read pointer signal is greater than or the same as the write pointer signal, the still flag is set and applied to the A/V decoder. 
   Then, the A/V decoder is switched to a still mode. While the A/V decoder is decoding the A/V bit streams upon receipt of it from the bit stream buffer, when the sequence end code is detected, the lastly decoded frame is repeatedly displayed, so that the still frame can be accurately and quickly displayed. 
   In addition, since it is not necessary to periodically read out the presentation time stamps from the A/V decoder to judge the time point when the still occurs, the time is less taken to process data, and the stability of the system is improved. 
   As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalence of such meets and bounds are therefore intended to be embraced by the appended claims.