Abstract:
To provide a frame synchronizer free of any loss of additional information added to frame data of an input video signal. An embodiment of the invention relates to a frame synchronizer for receiving a video signal having a first synchronization signal and frame data on a frame basis, writing the frame data to a memory on the frame basis in accordance with the first synchronization signal, and reading the frame data from the memory on the frame basis in accordance with a second synchronization signal of a frequency different from a frequency of the first synchronization signal to output the frame data, including: a synchronization signal generator generating the second synchronization signal having the frequency higher than a preset standard frequency. With such a configuration, it is possible to prevent the loss of the additional information added to the frame data in the input video data.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a frame synchronizer, an optical disk device, an information recording/reproducing apparatus, and a signal synchronizing method, and more specifically to a frame synchronizer, an optical disk device, an information recording/reproducing apparatus, and a signal synchronizing method, each of which is used for standardizing a frame period of a video signal multiplexed with additional information.  
         [0003]     2. Description of Related Art  
         [0004]     There has been a growing trend to multiplex a video signal used for displaying video information such as television or video images with various types of additional information as well as video information to be actually displayed. To be specific, signals during a so-called vertical blanking interval of the video signal can be multiplexed with subtitle information for displaying captions (subtitles) upon the image reproduction or multiplexed with an electronic program guide (EPC) for extracting program information.  
         [0005]     A video signal processing apparatus for receiving such a video signal including video information and additional information to reproduce or record the information extracts the video information and additional information from the received video signal on a frame basis. In this case, it matters whether or not the additional information can be correctly extracted.  
         [0006]     When the video signal processing apparatus extracts the additional information from the received video signal, a serious problem arises especially in such a case that a frame period of the received video signal is different from an intended frame period of the video signal processing apparatus. This is supposedly because the received video signal involves a jitter.  
         [0007]     To that end, a video signal processing apparatus having a function of adjusting the frame period of the received video signal into a fixed period, such as a frame synchronizer, has been under study and proposed (see Japanese Unexamined Patent Publication No. 2003-46805, for example).  
         [0008]     The video signal processing apparatus as disclosed in Japanese Unexamined Patent Publication No. 2003-46805 stops receiving video signals of one period until an internal processing of the video signal processing apparatus corresponding to one period is completed if a frame period of the received video signal is longer than a reference frame period for the internal processing of the video signal processing apparatus. Further, if the frame period of the receive video signal is shorter than the reference frame period for the internal processing of the video signal processing apparatus, the apparatus stops a video signal processing during a period in which the internal processing of the video signal processing apparatus corresponding to one period outpaces the input of the video signals of one period and instead, executes an internal processing of the next period.  
         [0009]     With such a method, if the frame period of the received video signal is shorter than the reference frame period for the internal processing of the video signal processing apparatus, none of the received video signals undergo the video signal processing. Here, as regards video information displayed on a screen, only image information of one frame that is generally 1/24 sec. or 1/30 sec. is not displayed, which does not adversely affect a display quality albeit a little deteriorated image quality. However, as for the additional information, there is a possibility that loss of the additional information of one period largely influences the whole data, and it is desirable to execute the video signal processing on all the video signals.  
         [0010]     As mentioned above, the conventional video signal processing apparatus has a problem in that all frame data of the input video signals cannot be processed.  
       SUMMARY OF THE INVENTION  
       [0011]     According to an aspect of the present invention, a frame synchronizer is provided. The frame receives a video signal having a first synchronization signal and frame data on a frame basis. The frame synchronizer includes a memory, a synchronization signal generator and a controller. The synchronization signal generator generates a second synchronization signal having a frequency different from the first synchronization signal and higher than a predetermined standard frequency. The controller writes the frame data to the memory on the frame basis in accordance with the first synchronization signal, and reads the frame data from the memory on the frame basis in accordance with the second synchronization signal to output the frame data.  
         [0012]     With such a configuration, the system clock having a frequency higher than the standard clock is generated and the synchronization signal is generated based on the generated system clock, so even if frame repeating occurs during a frame data read processing, frame skipping hardly occurs. As a result, it is possible to prevent a loss of additional information in the frame data.  
         [0013]     According to another aspect of the invention, a signal synchronizing method includes; receiving a video signal having a first synchronization signal and frame data on a frame basis, writing the frame data to a memory on the frame basis in accordance with the first synchronization signal, and reading the frame data from the memory in accordance with a second synchronization signal of a frequency different from a frequency of the first synchronization signal on the frame basis to output the read frame data. The second synchronization signal is generated to have the frequency higher than a preset standard frequency.  
         [0014]     According to this method, the system clock having a frequency higher than the standard clock is generated and the synchronization signal is generated based on the generated system clock, so even if frame repeating occurs during a frame data read processing, frame skipping hardly occurs. As a result, it is possible to prevent a loss of additional information in the frame data. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The above and other objects, advantages and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:  
         [0016]      FIG. 1  is a block diagram showing the configuration of a frame synchronizer according to an embodiment of the present invention;  
         [0017]      FIG. 2  is a flowchart of a processing flow at the data write time of the frame synchronizer according to the embodiment of the present invention;  
         [0018]      FIG. 3  is a flowchart of a processing flow at the data read time of the frame synchronizer according to the embodiment of the present invention;  
         [0019]      FIG. 4  is a block diagram showing a configuration example of a synchronization signal generator according to the embodiment of the present invention;  
         [0020]      FIG. 5  is a block diagram showing a configuration example of an oscillator according to the embodiment of the present invention;  
         [0021]      FIG. 6  is a block diagram showing a configuration example of an oscillator according to the embodiment of the present invention;  
         [0022]      FIG. 7  is a timing chart illustrative of data read/write timings according to the embodiment of the present invention;  
         [0023]      FIG. 8  is a timing chart illustrative of data read/write timings according to the embodiment of the present invention;  
         [0024]      FIG. 9  is a block diagram showing the configuration of an MPEG encoder of a DVD recording/reproducing apparatus according to an embodiment of the present invention; and  
         [0025]      FIG. 10  is a flowchart of a processing flow of the DVD recording/reproducing apparatus according to the embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes.  
       First Embodiment  
       [0027]      FIG. 1  is a block diagram showing the configuration of a frame synchronizer according to a first embodiment of the present invention. A frame synchronizer  1  includes a controller  10 , a memory  11 , a non-standard synchronous counter  12 , an internal synchronous counter  13 , an input buffer  14 , an output buffer  15 , and a synchronization signal generator  16 .  
         [0028]     The controller  10  is a control unit that executes various kinds of control in the frame synchronizer  1 . More specifically, the controller controls input/output of frame data in a video signal to/from a memory. The frame data implies image data and additional data which compose each frame. The controller  10  may execute various kinds of control using a special processor or a central processing unit (CPU) may execute various kinds of control based on a program.  
         [0029]     The memory  11  is a storage device for temporarily storing frame data sent from the input buffer  14  to output the frame data to the output buffer  15  in sync with an internal timing signal. The memory  11  includes a random access memory (RAM) or the like.  
         [0030]     The non-standard synchronous counter  12  is used for counting the number of input non-standard synchronous signals. The term “non-standard” means that a period of the input video signal is out of spec of a standard period of the frame synchronizer  1 . The frame synchronizer  1  receives and converts the video signal of the non-standard period into a signal of a standard period, and a non-standard synchronous signal is input in accordance with the non-standard period of the input video signal. The non-standard synchronous signal has a frame period aligned with the start or end of a frame of the frame data in the input video signal. The non-standard synchronous counter  12  receives the non-standard synchronous signal to count the number of frames based on the received non-standard synchronous signal. The non-standard synchronous counter  12  outputs a non-standard frame number in accordance with the count value of the frames to the controller  10 .  
         [0031]     The internal synchronous counter  13  receives an internal synchronization signal from the synchronization signal generator  16 . Further, the internal synchronous counter  13  counts the number of frames in accordance with the received internal synchronization signal. The internal synchronous counter  13  outputs an internal frame number based on a count value of the frames to the controller  10 .  
         [0032]     The input buffer  14  is a memory for temporarily storing frame data. The input buffer  14  stores the input frame data for each frame, and this data is read from the controller  10  and written to the memory  11 .  
         [0033]     The output buffer  15  is a memory for temporarily storing output frame data. The output buffer  15  stores frame data for each frame, and this data is sent to a corresponding device in step with the internal synchronization signal.  
         [0034]     The synchronization signal generator  16  generates an internal synchronization signal. How to generate the internal synchronization signal is described later in detail. The synchronization signal generator  16  supplies the generated internal synchronization signal to the internal synchronous counter  13 .  
         [0035]     It is desirable that the internal synchronization signal generated by the synchronization signal generator  16  have a period shorter than a period of the non-standard synchronous signal applied to the non-standard synchronous counter  12 . The period of the internal synchronization signal is determined by a selecting unit  16 . The selecting unit  16  may select an appropriate period in accordance with an input operation of a user or may automatically determine a period in accordance with the input video signal if possible.  
         [0036]      FIG. 2  is a block diagram showing a configuration example of the synchronization signal generator  16 . The synchronization signal generator  16  includes a selecting unit  160 , an oscillator  161 , and a timing generator  162 . The selecting unit  160  includes a selector  1600 , and mode memories  1601 ,  1602 , and  1603 .  
         [0037]     The selecting unit  160  functions to select a frequency of a system clock output from the oscillator  161 . The selecting unit  160  may select an appropriate frequency in accordance with a user&#39;s operation or may automatically select a frequency. The selecting unit  160  sends information about the selected frequency to the oscillator  161 .  
         [0038]     The oscillator  161  is a system clock generator for generating a system clock based on the information about the frequency applied from the selecting unit  160 . The oscillator  161  outputs the generated system clock to the timing generator  162 .  
         [0039]     The timing generator  162  generates an internal synchronization signal based on the system clock from the oscillator  161 . The timing generator  162  outputs the generated internal synchronization signal to the internal synchronous counter  13 .  
         [0040]     The selector  1600  received an instruction from a CPU  20  to select one of the frequency information supplied from the mode memories  1601 ,  1602 , and  1603  to output the selected frequency information to the oscillator  161 .  
         [0041]     The mode memories  1601 ,  1602 , and  1603  store frequency information. In the illustrated example of  FIG. 2 , the mode storages  1601 ,  1602 , and  1603  store VTR-mode frequency information, DVD-mode frequency information, and tuner-mode frequency information, respectively. These storages store the frequency information most suitable for the individual modes. Moreover, it is possible to set a mode in which the output frequency of the oscillator is always higher than the input clock frequency used for generating the non-standard synchronous signal. In this case, frequent repeat processes deteriorate the image quality, but the frame data can be obtained without fail. This mode is suitable for obtaining the additional information without fail at the sacrifice of video information. If the additional information is VBI information, this mode is called “VBI mode”.  
         [0042]     The CPU  20  may issue an instruction in accordance with a user&#39;s input operation with a remote controller, a keyboard, or a mouse or may automatically select an appropriate mode such as responding to the time or program specified by EPG information and setting “VBI mode” if the EPG information is input beforehand.  
         [0043]     The oscillator  161  generates a system clock with a frequency selected with the selecting unit  160 . There are two methods of controlling the output frequency of the oscillator  161 , that is, a voltage control method of  FIG. 3  and a phase locked loop (PLL) method of  FIG. 4 . According to the voltage control method, a VCXO (voltage controlled crystal oscillator) generates the system clock based on the preset analog voltage level. Meanwhile, according to the PLL method, a PLL circuit generates the system clock in accordance with a preset frequency dividing rate. The PLL circuit receives a signal for dividing an output signal frequency from an oscillating circuit into “n” from an output circuit. In this case, the resultant frequency is n/m of the output frequency of the oscillator. The oscillator  161  may be implemented in any form insofar as a system clock of a specified frequency can be supplied.  
         [0044]     Referring next to a flowchart of  FIG. 5 , a processing flow of a data write processing of the frame synchronizer  1  according to the present invention.  
         [0045]     First, the input buffer  14  receives and stores frame data in the video signal on a frame basis (S 11 ). Subsequently, the non-standard synchronous counter  12  receives a non-standard synchronous signal in the video signal to count the number of frames in accordance with the received non-standard synchronous signal (S 12 ). The non-standard synchronous counter  12  sends a frame number based on the count value of the frames to the controller  10 .  
         [0046]     Receiving the frame number from the non-standard synchronous counter  12 , the controller  10  reads frame data corresponding to the frame number from input buffer  14  and records the read frame data in the memory  11  (S 13 ). At this time, the controller  10  records the frame number and the frame data in association with each other.  
         [0047]      FIG. 6  is a flowchart of a data read processing of the frame synchronizer  1  according to the present invention. The data read processing starts in step with an input timing of the frame number from the internal synchronous counter  13 . First, the selecting unit  160  selects a system clock frequency (S 21 ). The selecting unit  160  output the selected frequency information to the oscillator  161  (S 22 ).  
         [0048]     The above system clock frequency is set higher than a standard clock frequency. The frequency of the synchronization signal generated based on the system clock is also set higher than the standard frequency. The standard clock and the standard frequency are determined based on the spec of the output data, for example. For example, in the case of converting the input video signal into MPEG (moving pictures experts group)-2 data, the frequency should be set to 27 Mhz. In this case, the system clock frequency is set to 27.00135 to 27.00405 Mhz, that is, preferably set about 50 to 150 ppm higher than the standard clock frequency.  
         [0049]     The oscillator  161  generates a system clock based on the input frequency information (S 23 ). The oscillator  161  generates the system clock and then outputs the generated system clock to the timing generator  162  (S 24 ). The timing generator  162  generates the internal synchronization signal based on the input system clock. For example, in the case of processing an NTSC (National Television System Committee) video signal, one frame includes 525 lines, and one line corresponds to  858  clock pulses, so the internal synchronization signal is generated every 450450 clock pulses (=525×858). The timing generator  162  sends the generated internal synchronization signal to the internal synchronous counter  13 .  
         [0050]     The internal synchronous counter  13  receives the internal synchronization signal from the timing generator  162  to count the number of frames based on the input internal synchronization signal (S 25 ). The internal synchronous counter  13  outputs a frame number based on the count value of the frames to the controller  10 .  
         [0051]     The controller  10  receives the frame number from the internal synchronous counter  13  to read the frame data stored in association with the frame number from the memory  11  and send the read data to the output buffer  15  (S 26 ). The read frame number is frame data corresponding to the frame number that has been written to the memory  11 .  
         [0052]     Referring next to  FIG. 7 , the data read/write timings are described.  
         [0053]     A non-standard synchronous signal waveform of  FIG. 7  is a waveform of the non-standard synchronous signal in the video signal, which is applied to the non-standard synchronous counter  12 . A non-standard frame number of  FIG. 7  shows the frame number obtained by the non-standard synchronous counter  12  counting the input non-standard synchronous signals and send to the controller  10  in accordance with the count value. An internal synchronization signal waveform of  FIG. 7  is a waveform of the internal synchronization signal generated with the synchronization signal generator  16  and supplied to the internal synchronous counter  13 . An internal frame number of  FIG. 7  shows the frame number obtained by the internal synchronous counter  13  counting the number of frames and then sent to the controller  10 .  
         [0054]     The non-standard frame number increments in accordance with a falling edge of the non-standard synchronous signal. At this time, the controller  10  reads frame data corresponding to the incremented frame number from the input buffer  14  and writes the read data to the memory  11 .  
         [0055]     The internal frame number increments in accordance with the failing edge of the internal synchronization signal. At this time, the controller  10  reads frame data corresponding to the incremented frame number from the memory  11  and sends the read data to the output buffer  15 . Here, the read frame data is frame data corresponding to the frame number that has been written to the memory  11  and thus, at a timing t 1  of  FIG. 7 , the frame data corresponding to the internal frame number  2  has been written. Hence, the read processing is executed with no problems. However, at a timing t 2 , the frame data corresponding to the internal frame number  3  has not been yet written, so the frame data corresponding to the frame number  2  is read again. This is called “frame repeating”.  
         [0056]     When the frame repeating occurs, the same frame is reproduced for two consecutive frames upon the image reproduction, so an image quality is somewhat deteriorated, but the loss of frame data never occurs, which means that the multiplexed additional information can be obtained without fail. Further, it is possible to check whether or not the frame repeating occurs at this point, so a frame repeating signal may be generated to send information about the frame repeating to a corresponding device such as an MPEG encoder. Receiving the information about the frame repeating, the MPEG encoder sets a repeat flag ON for the repeated frame data during the MPEG encoding. Thus, it is possible to prevent the same frame from being recorded redundantly.  
         [0057]     The frequency of the system clock generated by the oscillator  161  is set higher than the clock frequency of the input video signal as a reference of the non-standard synchronous signal applied to the non-standard synchronous counter  12 , so there is a possibility that frame repeating occurs, but frame skipping that is a phenomenon opposite to the frame repeating hardly occurs.  
         [0058]      FIG. 8  shows an example where the frame skipping occurs. In this case, the frequency of the non-standard synchronous signal is hither than the frequency of the internal synchronization signal. At a timing t 3  of  FIG. 8 , the frame data corresponding to the internal frame number  4  is read, but during this read processing, frame data corresponding to the non-standard frame numbers  5  and  6  has been written to the memory  11 . As a result, at a timing t 4 , the frame data corresponding to the internal frame number  6  is read following the data corresponding to the internal frame number  4 , so the data corresponding to the internal frame number  5  is skipped.  
         [0059]     The frame skipping occurs under such conditions that the non-standard synchronous signal frequency is higher than the standard clock frequency by 150 ppm or more. However, such a situation that the non-standard synchronous signal frequency is higher than the standard clock frequency by 150 ppm or more does not occurs, that is, the frame skipping does not occur except in special cases such as fast-forwarding/rewinding. Further, during the fast-forwarding/rewinding, the additional information is insignificant. Thus, in such a case, the frame skipping is allowed. Further, the system clock frequency may be set so as not to cause the frame skipping even under such conditions.  
         [0060]     In this way, the frame synchronizer according to the present invention sets the system clock frequency higher, making it possible to prevent frame skipping and obtain the multiplexed additional information without fail.  
       Second Embodiment  
       [0061]     Hereinbelow, an example of applying the frame synchronizer according to the present invention to a DVD recording/reproducing apparatus is described.  FIG. 9  is a block diagram showing the configuration of an MPEG encoder of a DVD recording/reproducing apparatus according to a second embodiment of the present invention.  
         [0062]     An MPEG encoder  2  of the DVD recording/reproducing apparatus according to the present invention includes a CPU  20 , a CPU interface  201 , a memory  21 , a frame synchronizer  22 , a video decoder  23 , and an MPEG encoder  24 .  
         [0063]     The CPU  20  is a controller for executing various kinds of control over the MPEG encoder  2  in the DVD recording/reproducing apparatus according to the present invention. The data exchange between the CPU  20 , and the frame synchronizer  22 , the video decoder  23 , and the MPEG encoder  24  is performed through the CPU interface  201 .  
         [0064]     The memory  21  is a storage device for storing a program or data for operating the MPEG encoder  2  of the DVD recording/reproducing apparatus. The memory  21  includes a RAM or the like.  
         [0065]     The configuration of the frame synchronizer  22  is the same as the frame synchronizer  1  according to the first embodiment of the invention, so its description is omitted here. For that matter, the CPU  20  doubles as the controller in the frame synchronizer, and the memory  21  may double as the memory  11  in the frame synchronizer.  
         [0066]     The video decoder  23  is a decoder for receiving an analog video signal and converting the signal into digital video data. The decoding may be executed by the CPU  20  using a program or by a special processor. The decoded digital video data is sent to the frame synchronizer  22 .  
         [0067]     The MPEG encoder  24  receives the video data standardized with the frame synchronizer  22  and converts the received data into MPEG data. The converted MPEG data is sent as an MPEG stream.  
         [0068]     Referring next to a flowchart of  FIG. 10 , a processing flow of the MPEG encoder  2  in the DVD recording/reproducing apparatus according to the second embodiment of the invention is described.  
         [0069]     First, the video decoder  23  receives and converts the analog video data to digital video data (S 31 ). The video decoder  23  sends the converted digital video data to the frame synchronizer  22 .  
         [0070]     The frame synchronizer  22  receives the digital video data from the video decoder  23  and then standardizes a frame period of the received digital video data (S 32 ). The way to standardize the data is the same as the first embodiment. The frame synchronizer  22  supplies the standardized video data to the MPEG encoder  24 .  
         [0071]     The MPEG encoder  24  receives and converts the standardized video data into MPEG data (S 33 ). The converted MPEG data is output to a corresponding device as the MPEG stream and recorded on a recording medium such as a DVD-R.  
         [0072]     In this way, the MPEG encoder  2  of the DVD recording/reproducing apparatus converts the received analog data into the MPEG data. Applying the frame synchronizer according to the present invention to this conversion makes it possible to prevent the loss of additional data. Further, the MPEG encoder  24  receives a frame repeating signal from the frame synchronizer  22 , thereby setting a repeating flag ON for the frame data repeated during the MPEG encoding to prevent the redundant recording of the same frame. As a result, it is possible to minimize extra streams.  
       Other Embodiments  
       [0073]     In the above embodiments, the MPEG encoding processing is executed as a post-processing of the frame synchronizer, but this processing may be executed by a video encoder or executed in parallel with the frame synchronizer.  
         [0074]     It is apparent that the present invention is not limited to the above embodiment and it may be modified and changed without departing from the scope and spirit of the invention.