Abstract:
An apparatus and method for recording multimedia data is disclosed. The apparatus and method employ a receiving unit for receiving compressed multimedia signal, a decoder unit for decoding the multimedia signal to convert it into a data stream having a predetermined format, a data compression unit for reducing the amount of data in the data stream by a certain amount and encoding it, a compression select unit for setting a compressibility of the data compression unit, and a storage unit for storing the encoded data. In accordance with the apparatus for recording the multimedia data, in the case where there is no need to record the video data with high quality, it is possible to increase the recording time of the multimedia data by reducing the data amount of the video signal using a variety of compression methods when the multimedia data is recorded in a storage device.

Description:
PRIORITY  
         [0001]    The present invention claims priority under 35 U.S.C. §119 from Korean Patent Application No. 2002-85381 filed Dec. 27, 2002 entitled “Apparatus for Recording Multimedia Data with High Efficiency,” the contents of which are incorporated herein by reference in their entirety.  
         BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to an apparatus and method for recording multimedia data such as a digital audio signal and a digital video signal, and more particularly, to an apparatus and method for recording multimedia data with greater efficiency such that the recording time of the multimedia data is increased.  
           [0004]    2. Brief Description of the Related Art  
           [0005]    Digital multimedia data, and in particular digital audio and video signals, are considerably larger in terms of file space occupancy, and so on, as compared to analog multimedia data. In a case where digital multimedia data is stored on storage devices such as a memory or a hard disk drive (HDD), the recording time of the storage devices is slower than for analog multimedia data.  
           [0006]    [0006]FIG. 1 is a block diagram of a conventional set top box capable of recording digital multimedia data. The set top box shown comprises a tuner  10 , a demodulator  20 , a demultiplexer  30 , a hard disk drive (HDD)  40 , MPEG decoder  50 , and a video encoder  60 . The tuner  10  receives broadcasting signals being sent via a broadcast station or cable networks, and selects one of the received broadcasting signals.  
           [0007]    The demodulator  20  removes the carrier wave from the broadcasting signal selected by the tuner  10 . The broadcasting signals having the carrier wave removed by the demodulator comprises a digital data stream which the broadcast station intended to transmit. In general, the digital data stream is encoded in MPEG-2 format. Accordingly, the digital data stream is compressed based on the MPEG-2 standard.  
           [0008]    Demultiplexer  30  separates the digital data stream into a video signal and an audio signal. The hard disk drive (HDD)  40  stores the video signal and the audio signal which were separated by the demultiplexer  30 . At this time, the video signal and the audio signal stored on the hard disk drive (HDD)  40  are compressed according to MPEG-2 standard.  
           [0009]    MPEG decoder  50  and the video encoder  60  reproduce the video signal and audio signal stored on the hard disk drive (HDD). MPEG decoder  50  decompresses the compressed video signal and audio signal according to a standard such as the MPEG-2 standard, and the video encoder  60  converts the decompressed signals into the video format of image display devices such as a television. The video format is typically either NTSC or PAL, although those of ordinary skill in the art will appreciate that any suitable video format of a display device is acceptable and is considered to be within the spirit of the present invention.  
           [0010]    On the other hand, in a set top box having the configuration described above, in a case where a user desires to record broadcasting programs that are supplied via the tuner  10  having a long duration, it is required to increase the capacity of the hard disk drive (HDD) or to erase the previous data stored on the hard disk drive (HDD)  40 . One way to increase the capacity of the hard disk drive (HDD)  40 , is to add an additional hard disk drive (HDD). However, this disadvantageously increases the cost of manufacturing the set top box.  
           [0011]    There is no need to store the video signal on the hard disk drive (HDD)  40  with high quality if the programs are news programs or musical programs of which the principal object is for listening. Nevertheless, conventionally the capacity of the hard disk drive (HDD) is unnecessarily consumed by storing the video signal based on the MPEG-2 standard on the hard disk drive (HDD)  40  for all programs.  
         SUMMARY  
         [0012]    The above described problems are substantially overcome and other advantages are realized by embodiments of the present invention. It is one aspect of the present invention to provide an apparatus for recording multimedia data with the recording time of the multimedia data being increased.  
           [0013]    In order to accomplish the above aspects and to realize other advantages of the present invention, a recording apparatus according to an embodiment of the present invention comprises a receiving unit for receiving a compressed multimedia signal, a decoder unit for decoding the multimedia signal to convert it to data stream having a predetermined format, a data compression unit for reducing and encoding the amount of the data stream by a certain amount, a compression select unit for setting the compressibility of the data compression unit, and a data storage unit for storing the encoded data.  
           [0014]    The decoder unit preferably comprises a demodulator for removing the carrier wave from the received broadcast multimedia signal, a demultiplexer for decoding the multimedia signal having the carrier wave removed and separating it into video signal and audio signal, and a decoder for decompressing the compressed video signal and the audio signal.  
           [0015]    Preferably, the decoder unit further comprises a format setting unit for setting the format of the video and audio signals outputted from the demultplexer to be one of PES (Packetised Elementary Stream) in a packet unit and TS (Transport Stream) in a pack unit.  
           [0016]    The data compression unit preferably comprises a data conversion unit for reducing a portion of data making up the decompressed video and audio signals according to the compressibility set by the compression select unit, and an encoder for recompressing the video data and audio data having a predetermined portion of data reduced by the data conversion unit.  
           [0017]    The data conversion unit preferably comprises a memory for storing the decompressed data from the decoder in a frame unit; a frame setting unit, enabled by the compression select unit, for removing frames of the data stored on the memory (such as even-numbered frames), and to re-store it on the memory; and an encoder for compressing the data stream re-stored on the memory.  
           [0018]    Preferably, the data conversion unit further comprises a format conversion unit, enabled by the compression select unit, for converting the signal format of the video signal stored on the memory into 4:2:0 format to re-store on the memory.  
           [0019]    Preferably, the data conversion unit further comprises a scaler that is enabled by the compression select unit and reduces the resolution of the video signal stored in frame unit on the memory to a certain resolution before re-storing the video signal having the reduced resolution in the memory.  
           [0020]    The compression select unit preferably generates a first control signal that causes the video signal and the audio signal to be outputted to any one of the decoder and the storage unit by controlling the demultiplexer, and a second control signal that causes at least one of the frame setting unit, the format conversion unit, and the scaler to be enabled by controlling the data conversion unit.  
           [0021]    Preferably, the format described above is any one of MPEG-1, MPEG-2, MPEG-3, and MPEG-4. Also, the receiving unit receives a multimedia signal having any one of MPEG-1, MPEG-2, MPEG-3, and MPEG-4 formats. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The present invention will be described in connection with a particular embodiment thereof, and will be better understood with reference to the accompanying drawing figures, in which:  
         [0023]    [0023]FIG. 1 is a block diagram of a conventional set top box capable of recording digital multimedia data;  
         [0024]    [0024]FIG. 2 is a block diagram of a set top box having a device for storing multimedia data according to an embodiment of the present invention; and  
         [0025]    [0025]FIG. 3 is a detailed block diagram of a data compression unit according to an embodiment of the present invention. 
     
    
       [0026]    It should be understood that in the drawing figures, like reference numbers refer to like features and structures.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    The above mentioned objects, as well as other objects, features and advantages of an embodiment of the present invention will be better understood from the following description taken in conjunction with the attached drawing figures.  
         [0028]    [0028]FIG. 2 is a block diagram of an example of a set top box having a device for storing multimedia data according to an embodiment of the present invention. The set top box shown comprises a tuner  100 , a decoder unit  200 , a data compression unit  300 , a compression select unit  400 , a hard disk drive (HDD)  500 , a decompression unit  600 , and a video encoder  700 .  
         [0029]    The tuner  100  selects one of a plurality of broadcasting signals supplied via broadcast stations or cable networks according to a predetermined channel. At this time, the received broadcasting signal is typically encoded in any one of the MPEG-1-MPEG-4 standards, and it will be described on the basis of MPEG-2 format in this embodiment. Thus, the broadcasting signal selected by the tuner  100  is the video signal and audio signal based on MPEG-2 format that is modulated with a carrier wave having a predetermined frequency.  
         [0030]    The decoder unit  200  removes the carrier wave from the broadcasting signal selected by the tuner  100  and decodes it, thereby converting the signal to a data stream having a predetermined format (MPEG-2 in the described example).  
         [0031]    The data compression unit  300  is controlled by the compression select unit  400 , and receives the data stream outputted from the decoder unit  200  and reduces the data size of the data stream according to at least one method. In order to reduce the data size of the data stream, this embodiment uses any one of three methods. The first is a method for converting a video signal having typically a 4:4:2 format to a 4:2:0 format. The second is a method for removing even-numbered frames of the video signalThe third is a method for reducing the resolution of the video signal. These methods will be described in further detail below.  
         [0032]    The compression select unit  400  generates, in response to a control signal generated from a setting key (not shown) or a remote controller (not shown) included in the present set top box, a control signal (sel 1 ) for setting the output direction of the data stream outputted from the demultiplexer  220 . Based on the control signal (sel 1 ), the output of demultiplexer  220  can be provided to decoder  240  or to hard disk drive  500 . Compression select unit  400  also generates a control signal (sel 2 ) for setting the compression method of the supplied data stream in the data compression unit  300 . Also, compression select unit  400  generates a control signal (sel 3 ) for enabling/disabling the decompression unit  600 . Furthermore, compression select unit  400  generates a control signal (sel 4 ) for setting the format of the data stream outputted from the decoder unit  200 . Here, the control signal (sel 2 ) is composed of 2 bits for setting three compression methods. The selected compression method may use only one of the above-described methods, or may use a combination of the above-described methods. For example, it is possible to convert the format of the video signal to 4:2:0 format while also reducing the resolution of the data stream having MPEG format outputted from the decoder unit  200 .  
         [0033]    The hard disk drive (HDD)  500  stores the video signal and the audio signal in MPEG format compressed by the data compression unit  300  according to the method selected by the compression select unit  400 . The amount of data stored on the hard disk drive (HDD)  500  depends on the combination of the methods selected by the compression select unit  400 , and it is possible to store the video signal and the audio signal reduced to {fraction (1/16)} according to the selection of the compression method on the video signal and the audio signal. In other words, the capacity of data storage can be dramatically increased with a device according to an embodiment of the present invention.  
         [0034]    The decompression unit  600  performs MPEG decoding on the video signal and the audio signal stored in the hard disk drive (HDD)  500 . In a video encoder  700 , the decoded video signal and audio signal are converted into the video format of NTSC/PAL according to the control signal (sel 4 ) from the compression unit  400 .  
         [0035]    Preferably, the decoder unit  200  includes a demodulator  210 , a demultiplexer  220 , a format setting unit  230 , and a decoder  240 .  
         [0036]    The demodulator  210  removes the carrier wave from the broadcasting signal selected by the tuner  100 . The broadcasting signal having the carrier wave removed by the demodulator  210  comprises the digital data stream which the broadcast station intended to transmit. In this embodiment, the digital data stream has MPEG- 2  format, and is compressed based on MPEG-2 standard.  
         [0037]    The demultiplexer  220  separates the digital data stream into a video signal and an audio signal, and the hard disk drive (HDD)  500  stores the video signal and the audio signal separated by the demultiplexer  220 . At this time, the video signal and the audio signal held in the hard disk drive (HDD)  500  are compressed according to MPEG-2 standard. Additionally, the demultiplexer  220  directly sends the video signal and the audio signal to the hard disk drive (HDD)  500  when the control signal (sel 1 ) from the compression select unit  400  is enabled. Consequently, in the case of a video signal requiring high quality, it is possible to store the video signal in the hard disk drive (HDD) without carrying out a separate compression process.  
         [0038]    The format setting unit  230  sets, in response to the control signal (sel 4 ) from the compression select unit  400 , the data stream having MPEG-2 format outputted from the demultiplexer  230  to be any one of PES format in a packet unit and TS format in a pack unit. The format setting unit  230  preferably sets the output of the demultiplexer  220  to be TS format when the control signal (sel 4 ) is enabled, and the output of the demultiplexer  220  to be PES format when the control signal (sel 4 ) is disabled. Here, if the data stream is PES unit, the data stream from the demultiplexer  230  is supplied to the decoder  240  as it is, and has a signal format capable of being stored in a scrambled format on the hard disk drive (HDD). If the data stream is TS unit, the output of the demultiplexer  220  may be stored on the hard disk drive (HDD)  500  in unscrambled format. The scrambling term used herein refers to the broadcast station or the enterpriser of the cable networks encoding the broadcasting signal so that only viewers authorized to view the broadcasting signal are able to watch the broadcasting signal. The format setting unit  230  causes the broadcasting signal to be stored under encoding or to be decoded before being stored. The decoder  240  performs MPEG decoding on the video signal and the audio signal.  
         [0039]    Preferably, the data compression unit  300  comprises a data conversion unit  310  and an encoder  320 . The data conversion unit  310  is controlled by the compression select unit  400 , and reduces the amount of data in the decompressed video signal and audio signal from the decoder  240  depending on one of the three methods discussed above. The first method converts a video signal having 4:4:2 format to a video signal having 4:2:0 format. The second method removes even-numbered frames of the moving video signal. The third method reduces the resolution of the video signal. The encoder  320  compresses the data stream having the data amount removed according to MPEG-2 format.  
         [0040]    [0040]FIG. 3 is a detailed block diagram of an example of the data compression unit  300 . The data compression unit  300  comprises a memory  311 , a frame setting unit  312 , a format conversion unit  313 , and a scaler  314 .  
         [0041]    The memory  311  receives the video signal and the audio signal decompressed by the decoder  240  and stores it in a frame unit. The frame setting unit  312  is enabled/disabled by the control signal (sel 2 ) supplied from the compression select unit  400 , and when enabled, receives the video signal stored in the memory  311  before removing even-numbered frames of the video signal and then resending the remaining frames to the memory. Thereby, the video signal having the even-numbered frames removed is stored in the memory  311 .  
         [0042]    The format conversion unit  313  is enabled/disabled by the control signal (sel 2 ), and when enabled, converts the format of the video signal held in the memory  311  to 4:2:0 format. The 4:2:0 format is the ratio of the sampling frequencies of the luminance signal to the color difference signals, and is a method representing the video signal based on International Telecommunication Union-Radio Communication Sector (ITU-R) recommendation  601  standard. This format reduces the data amount of the video signal by using the characteristic that the human eye is sensitive to the luminance signal, whereas it is less sensitive to color difference signals. The format of a video signal not having the color difference signal (Cb, Cr) removed is referred to as 4:4:4 format. The format of a video signal having the color difference signals (Cb, Cr) reduced to ½ for compressing the video signal is referred to as 4:2:2 format. The format of a video signal having the color difference signals (Cb, Cr) reduced to ¼ is referred to as 4:2:0 format. MPEG-2 format generally transmits/receives the video signal by means of 4:2:2 video format, and the format conversion unit converts the video signal having 4:2:2 video format into a video signal having 4:2:0 video format, thereby reducing the data amount of the video signal by half.  
         [0043]    The scaler  314  is enabled/disabled by the control signal sel 2 , and when enabled, reduces the resolution of the video signal held in the memory  311 . For example, if the resolution of the video signal inputted is 800×600, the scaler  311  reduces it to 640×480 or less. The video signal having the resolution reduced is re-stored in the memory  311 . Thereby, the video signal held in the memory  311  is reduced in the data amount as compared with the video signal supplied to the tuner  100 , and hence when the reduced data is stored in the hard disk drive (HDD)  500 , the available recording time of the multimedia data becomes longer.  
         [0044]    Although a particular exemplary embodiment of the present invention has been disclosed with reference to the appended drawing figures and the preferred embodiments of the present invention corresponding to the drawing figures has been described, it should be understood that the descriptions in the present specification are only for illustrative purpose, and not for limiting the scope of the present invention.  
         [0045]    Also, those who are skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the present invention. Therefore, it should be understood that the present invention is limited only to the accompanying claims and the equivalents thereof, and includes the aforementioned modifications, additions and substitutions.