Abstract:
A video and audio data synchronization method for a high-definition multimedia interface (HDMI) having a plurality of channels for outputting video and audio data includes determining a boundary between a control period and a data/video period in each of the plurality of channels, adjusting timing sequences of the plurality of channels respectively according to the boundaries, and simultaneously outputting video and audio data of the plurality of channels according to the timing sequences of the plurality of channels. This method can prevent loss of synchronization between channels due to layout and process variation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a video and audio synchronization method and related apparatus for a multimedia interface, and more particularly, to a video and audio synchronization method and related apparatus utilizing a boundary between a control period and a data/video period of HDMI serial video and audio data for calibrating and synchronizing timing sequences of data transmission in a plurality of data channels. 
         [0003]    2. Description of the Prior Art 
         [0004]    With the popularity of digital televisions, DVD display devices, and high definition flat panel displays, the time when people can really enjoy videos with high definition and high quality has finally arrived. However, the mainstream of signal transmission interfaces for flat panel displays is still based on conventional analog interfaces that have limitations of transmission distance and signal bandwidth. Furthermore, the flat panel displays have to convert the analog signals into digital signals through built-in analog-to-digital converters. In this case, not only does there exist a great energy loss in the signal conversion, but the transmission distance is also less than 2 to 3 meters. Therefore, in order to solve the problem, seven companies, including Intel et al., provided a specialized signal transmission interface for digital display devices: Digital Visual Interface (DVI). DVI is utilized for transmitting video signals in digital format to display devices. Since operations such as coding, compression, and error correction can be performed on digital signals, the transmission distance can be extended to 10-20 meters, and high quality images can also be obtained. However, the size of DVI connector is large, and audio signals cannot be transmitted through DVI, so DVI is mainly used for image data transmission between computers and display devices. 
         [0005]    Based on DVI, a high definition multimedia interface (HDMI) is a transmission interface specifically designed for next generation multimedia video and audio devices. HDMI is suitable for digital televisions, DVD recorders and players, set-top boxes, and other multimedia electronic devices. Different from transmitting the audio and video signals separately, the most significant characteristic of HDMI is that the video and audio signals are integrated and transmitted together through HDMI. In HDMI, uncompressed digital data transmission is utilized for eliminating signal interference and attenuation effectively in conversion of digital and analog signals. Compared with DVI, not only is the size of HDMI connector smaller, but the audio signals and the control signals for the devices can also be transmitted with the video signals. Furthermore, a high bandwidth digital content protection (HDCP) technique can be added in HDMI for preventing image data from being copied illegally. 
         [0006]    Please refer to  FIG. 1 .  FIG. 1  is a schematic diagram of an HDMI transmission and reception system  100 . The HDMI interface utilizes a transition minimized differential signaling (TMDS) method for coding, and includes four data transmission channels, three of which (TMDS channel  0  through TMDS channel  2 ) are utilized for transmitting video and audio data, and the other of which is utilized for transmitting clock data. A display data channel (DDC) is utilized for reading an extended display identification data (EDID) indicating the display characteristics of the receiving end, such as resolution, etc. First, the transceiver  110  converts and synthesizes the video and audio data into a format capable of being received by the receiver  120 . The transceiver  110  then encodes the video and audio data by TMDS, converts the video and audio data from parallel format to serial format, and transmits the serial data by low voltage differential signaling (LVDS). Note that, the operation of the receiver  120  is the same as that of the transceiver  110 , but the operation sequence is opposite. 
         [0007]    Generally speaking, the transceiver  110  outputs respectively the ordered serial video and audio data into the TMDS channels at the same time. However, due to layout or process variation, the length, impedance, gain, and attenuation of each TMDS channel are different, such that the data transmission in each TMDS channel is delayed by a different amount. That is, the timing sequence is shifted by different amounts. In this case, the receiver  120  cannot receive the video and audio data transmitted in the TMDS channels simultaneously. Therefore, in order to enable the receiver  120  to acquire all of the desired video and audio data correctly, it is very important to calibrate and synchronize the timing sequence of the data transmission channels. However, the method and the related apparatus for calibrating the timing sequence of the data transmission channels is not set forth in the HDMI specification and in the prior art. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore a primary objective of the present invention to provide a video and audio synchronization method and related apparatus for a multimedia interface. 
         [0009]    The present invention discloses a video and audio data synchronization method for a multimedia interface having a plurality of channels for outputting video and audio data comprising: determining a boundary between a first data period and a second data period in each of the plurality of channels; adjusting timing sequences of the plurality of channels respectively according to the boundary between the first data period and the second data period in each of the plurality of channels; and outputting the video and audio data of the plurality of channels simultaneously according to the timing sequences of the plurality of channels. 
         [0010]    The present invention further discloses a video and audio data synchronization apparatus for a multimedia interface having a plurality of channels for outputting video and audio data comprising: a decision unit for determining a boundary between a first data period and a second data period in each of the plurality of channels; a timing sequence adjustment unit coupled to the decision unit for adjusting timing sequences of the plurality of channels respectively according to the boundary between the first data period and the second data period in each of the plurality of channels; and an output unit coupled to the timing sequence adjustment unit for outputting the video and audio data of the plurality of channels simultaneously according to the timing sequences of the plurality of channels. 
         [0011]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic diagram of an HDMI transmission and reception system. 
           [0013]      FIG. 2  is a schematic diagram of data formats transmitted by TMDS channels. 
           [0014]      FIG. 3  is a schematic diagram of a video and audio data synchronization process for HDMI according to the present invention. 
           [0015]      FIG. 4  is a schematic diagram of an embodiment of the process according to the present invention. 
           [0016]      FIG. 5  is a function block diagram of a video and audio data synchronization apparatus for HDMI according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    For clearly illustrating the present invention, data formats transmitted by transition minimized differential signaling (TMDS) channels are stated in the following. Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram of the data formats transmitted by the TMDS channels. As shown in  FIG. 2 , the data transmitted in the TMDS channels can be divided into three data periods: a packet data period  210 , a video data period  220 , and a control period  230 . The packet data period  210  is utilized for transmitting audio and auxiliary signals of the video and audio data in a packet format. The video data period  220  is utilized for transmitting image data of pixels of the video and audio data. The control period  230  is utilized for transmitting preambles of the video and audio data, which indicate to a decoder whether the upcoming data period is a packet data period  210  or a video data period  220 . Therefore, the control period  230  always precedes the packet data period  210  and the video data period  220 . In other words, there must be a control period  230  between any two data periods including video and audio data. 
         [0018]    Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram of a video and audio data synchronization process  30  for a high density multimedia interface (HDMI) according to the present invention. The process  30  is utilized for synchronizing a timing sequence of HDMI data channels, and comprises the following steps: 
         [0019]    Step  300 : Start. 
         [0020]    Step  310 : Determine a boundary between a first data period and a second data period in each of the plurality of channels. 
         [0021]    Step  320 : Adjust timing sequences of the plurality of channels respectively according to the boundary between the first data period and the second data period in each of the plurality of channels. 
         [0022]    Step  330 : Output the video and audio data of the plurality of channels simultaneously according to the timing sequences of the plurality of channels. 
         [0023]    Step  340 : End. 
         [0024]    According to the process  30 , when a receiver receives serial video and audio data transmitted by the plurality of HDMI data channels, the present invention determines a boundary between a first data period and a second data period in each of the plurality of channels, adjusts timing sequences of the plurality of channels respectively according to the boundary between the first data period and the second data period in each of the plurality of channels, and outputs the video and audio data of the plurality of channels simultaneously. 
         [0025]    As shown in  FIG. 2 , the HDMI interface includes the three data transmission channels (TMDS channel  0  through TMDS channel  2 ) for transmitting serial video and audio data encoded by TMDS. The serial video and audio data transmitted in the TMDS channels can be divided into three kinds of data periods: a packet data period, a video data period, and a control period. Note that the packet data period and the video data period are the data periods including video and audio information. In the present invention, the first data period corresponds to the control period, and the second data period corresponds to the packet data period or the video data period. After determining the boundary between the control period and the data/video period in each channel, the timing sequences of the other two channels are adjusted respectively according to the boundary between the control period and the data/video period in a fist data channel (Step  320 ). In the present invention, the first data channel can preferably be the TMDS channel  0 . Finally, according to the timing sequence of the three data channels, an output device can output the serial video and audio data of the three data channels simultaneously, so that the video and audio data in the plurality of channels can be synchronized for decoding by a decoder (Step  330 ). Please note that the boundary between the control period and the data/video period in each channel can be determined according to a data pattern difference between the control period and the data/video period. 
         [0026]    For example, please refer to  FIG. 4 .  FIG. 4  is a schematic diagram of an embodiment of the process  30 . As shown in  FIG. 4 , since the length and the impedance of each channel are different, the data transmitted in each channel is delayed by different amounts. Blocks  400 ,  410 , and  420  are the control periods of TMDS channel  0  through TMDS channel  2 , respectively; and blocks  405 ,  415 , and  425  are the data/video periods of TMDS channel  0  through TMDS channel  2 , respectively. When an HDMI receiver receives serial video and audio data transmitted by TMDS channel  0  through TMDS channel  2 , the present invention determines the boundaries  403 ,  413 , and  423  between the control period and the data/video period in each channel first. Then, based on the boundary  403  between the control period and the data/video period in TMDS channel  0 , the timing sequences of the other two data channels are adjusted respectively, that is, the timing sequence of TMDS channel  1  is adjusted forward by a period t 1  and the timing sequence of TMDS channel  2  is adjusted back by a period t 2 . Finally, the serial video and audio data of the three data channels can be outputted simultaneously, so that the video and audio data in the channels is synchronized for decoding by a decoder. 
         [0027]    Please refer to  FIG. 5 .  FIG. 5  is a function block diagram of a video and audio data synchronization apparatus  50  for HDMI according to the present invention. The video and audio data synchronization apparatus  50  is utilized for realizing the process  30 , and comprises a decision unit  510 , a timing sequence adjustment unit  520 , and an output unit  530 . The decision unit  510  can determine the boundary between the control period and the data/video period in each of the TMDS channels according to specific data patterns of the control period. The timing sequence adjustment unit  520  can adjust the timing sequences of the other two data channels (TMDS channel  1  and TMDS channel  2 ) respectively based on the boundary between the control period and the data/video period in TMDS channel  0  according to a decision result of the decision unit  510 . Finally, the output unit  530  can output the serial video and audio data of TMDS channel  0  through TMDS channel  2  simultaneously for decoding by a decoder according to the adjusted timing sequence of each channel. In another embodiment, the timing sequence adjustment unit  520  further includes a buffer (not shown in  FIG. 5 ) for temporarily storing the video and audio data of the plurality of channels. 
         [0028]    As mentioned above, the present invention provides a video and audio synchronization method and related apparatus for HDMI. The present invention utilizes the boundary between the control period and the data/video period of the serial video and audio data in each TMDS channel for calibrating and synchronizing the timing sequences of data transmission in the plurality of channels, so that the decoder of the display devices can correctly return the desired video and audio data from the plurality of video and audio data transmission channels. Furthermore, convenience in circuit design can also be increased. 
         [0029]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.