a preferred embodiment of the present invention will now be described in detail with reference to the annexed drawings . in the drawings , the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings . in the following description , a detailed description of known functions and configurations incorporated herein has been omitted for conciseness . fig3 illustrates a construction of a demultiplexing device of a digital broadcasting receiver according to the present invention . the present invention provides fort demultiplexing that is separately performed as a first demultiplexing and second demultiplexing . a second demultiplexing unit 200 has the same basic construction as in fig1 . its detailed description has therefore been omitted . however , the second demultiplexing unit 200 is enabled to search for a program association table ( pat ), a program map table ( pmt ), and an intra frame only when a first demultiplexing unit 300 fails to search for the pat , the pmt , and the intra frame . if the first demultiplexing unit 300 succeeds in searching for the pat , the pmt , and the intra frame , the second demultiplexing unit 200 does not search . if any information is not searched during the first demultiplexing , then during second demultiplexing , the non - searched information will be searched again . in an exemplary embodiment , the first and second demultiplexing units 300 and 200 share flag information . the flag information refers to three flags representing whether or not to succeed in searching for the pat , the pmt , and the intra frame . reference symbol “ sw ” represents that the second and first demultiplexing units 200 and 300 are switched in operation . the second and first demultiplexing unit 200 and 300 are operated under the control of a controller ( not shown ). the controller controls the switching to perform the second demultiplexing after the first demultiplexing . the first demultiplexing is to search for necessary information from a transport stream ( ts ) without reproducing video or audio data . the necessary information refers to the pat , the pmt , and the intra frame . this information is necessary for confirming whether or not a received ts packet is an audio / video ts packet of a broadcasting ( note : here “ broadcasting channel switchover ” or “ channel switchover ” denotes that a specific desired broadcasting is selected by a viewer ) requested by the viewer . the video or audio data is outputted from the first and second demultiplexing units 300 and 200 , respectively , and is transmitted to and buffered in ring buffers ( vid and aud ) 100 and 150 . fig4 is a block diagram illustrating a detailed construction of the first demultiplexing unit of fig3 . if the viewer inputs a desirable broadcasting channel to view , the digital broadcasting receiver detects the inputting of the broadcasting channel and receives the ts packets . if the digital broadcasting receiver receives the ts packets , a ts buffer 31 buffers the received ts packets . an amount of data buffered in the ts buffer 31 is set to be much greater than that of data buffered in a ts buffer 22 of fig1 . a pat searcher 33 searches the buffered ts packets of the ts buffer 31 for the pat . if the pat searcher 33 succeeds in searching for the pat , it obtains a packet identification ( pid ) list of the broadcasting channel and the pmt from the searched pat , and obtains a pid of the pmt of the broadcasting channel that the viewer desires to view . further , the pat searcher 33 informs a pmt searcher 35 of its success in searching for the pat . a control signal ( c 1 ) is a signal for the pat searcher 33 to inform the pmt searcher 35 of its success in searching for the pat . in response to the control signal ( c 1 ) informing the success in searching for the pat , on the basis of the pid of the pmt of the broadcasting channel that the viewer desires to view , the pmt searcher 35 analyzes a header of the ts packets buffered in the ts buffer 31 and confirms whether the ts packet is the pmt , thereby searching for the corresponding pmt . if the pmt searcher 35 succeeds in searching for the pmt , it obtains a pid of an audio / video packetized elementary stream ( pes ) of the corresponding broadcasting channel from the searched pmt . further , the pmt searcher 35 transmits a control signal ( c 2 ) for informing an intra frame searcher 37 of its success in searching for the pmt . in response to the control signal ( c 2 ), on the basis of the obtained pid of the audio / video pes , the intra frame searcher 37 analyzes the header of the ts packets buffered in the ts buffer 31 and confirms whether the ts packet is the intra frame , thereby searching for the intra frame . if the intra frame searcher 37 also succeeds in searching for the intra frame , a video demultiplexer 39 and an audio demultiplexer 41 analyze the header of the ts packets buffered in the ts buffer 31 , search for a video or audio ts packet of the corresponding broadcasting channel , demultiplex the searched video or audio ts packet , and output the video and audio data . the video and audio data are transmitted to and buffered in the corresponding ring buffers ( vid and aud ) 100 and 150 , respectively . if it succeeds in obtaining program information ( search for pat , pmt , and intra frame ), a subsequent operation is performed in the second demultiplexing unit 200 . if the first demultiplexing unit 300 performs the demultiplexing one time and succeeds in obtaining the program information , the second demultiplexing unit 200 can directly perform video or audio demultiplexing but , if it fails , the first demultiplexing unit 300 will repeat the demultiplexing a predetermined number of times . if the first demultiplexing unit 300 fails to obtain the program information even after the first demultiplexing has been performed the predetermined number of times , the second demultiplexing unit 200 can first obtain the program information and then , perform the video or audio demultiplexing as in the conventional art . in comparison with fig1 , there is a difference in that , by separately performing the first demultiplexing , it is not required to discard the previous buffered ts data and again buffer the subsequent ts data when it fails to search for the pat , the pmt , or the intra frame . a capacity of the buffered ts data for the first demultiplexing is relatively greater than that of the second demultiplexing . for example , in the fist demultiplexing , the ts data received for about two seconds is stored . in the second demultiplexing , the ts data of merely about several to tens of packets are buffered . this is because it is a scheme for constantly storing predetermined data in the video / audio ring buffers ( vid and aud ) 100 and 150 of the rear stage and , by so doing , the video / audio can be stably reproduced . however , since the video / audio are not reproduced during the first demultiplexing , the entire system is not influenced in stability even though a large amount of ts data is buffered and simultaneously demultiplexed . as a result , the inventive demultiplexing is effective in that a large amount of ts data can be reused . in other words , as in fig1 , when conventional demultiplexing is performed , the pat / pmt are sequentially searched . however , as in fig3 and 4 , when the first demultiplexing is performed with the demultiplexing divided into the first and second demultiplexings , the pat is first searched , the pmt is again searched from the beginning without discarding the buffered ts data , and even the intra frame is similarly searched using the initially stored ts data from the beginning . if so , only a buffering time for the first demultiplexing is invested , and a time taken to searching for the pat / pmt is avoided . simply , the video / audio data are demultiplexed directly from the data buffered for the first demultiplexing . fig5 illustrates an example for describing a video start time point based on the demultiplexing according to the present invention . for the initial 2 seconds , the ts data is buffered . the pat can be searched at 0 . 4 seconds ( 1 st ), but the pmt is searched at 0 . 3 seconds with reuse of the buffered data ( 2 nd ), and the intra frame is searched at 0 . 1 second with reuse of the buffered data ( 3 rd ), thereby performing the demultiplexing . as a result , the video data corresponding to 1 . 9 seconds is directly demultiplexed and therefore , can be displayed at once for the viewer . the viewer waits only for the initial 2 seconds before viewing the picture through the screen of the display unit . accordingly , in comparison to a time of 3 . 1 seconds taken to perform the demultiplexing of fig1 , a channel switchover time can be reduced by one or more seconds in speed . switching to the second demultiplexing can be performed in a weak electric field where a desired pat / pmt is not searched with the first demultiplexing . the present invention has an advantage in that the demultiplexing of the ts packets is performed separately into the first demultiplexing and the second demultiplexing , thereby minimizing the time taken to search for the pat , the pmt , and the intra frame , and improving a channel switchover speed . while the invention has been shown and described with reference to a certain preferred embodiment thereof , it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims .