Abstract:
In a method and system for 3D comb synchronization and alignment of standard and non-standard video signals, a coarse synchronization is performed on a bottom frame, a current frame, and a top frame based on a bottom frame field count. The current frame is assigned the frame transferred immediately prior to a bottom frame whereas the top frame is assigned the frame transferred two frames. A current frame window signal and a top frame window signal may be used to lock the current frame and the top frame to a bottom frame vertical sync signal. After coarse synchronization, the video frames are finely aligned by correlating a phase difference between the subcarrier signals in each frame and modifying the phase difference until the correlation results in a specified phase locked value range. This method and system may facilitate the handling of video stream switching and non-standard data streams.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE  
       [0001]     This application makes reference to, claims priority to, and claims the benefit of U.S. Provisional Application Ser. No. 60/542,945, entitled “Method for 3D Comb Synchronization and Alignment of Standard and Non-Standard Video Signals,” filed on Feb. 9, 2004.  
         [0002]     This application makes reference to U.S. application Ser. No. (Attorney Docket No. 15500US02) filed on Jun. 24, 2004.  
         [0003]     The above stated applications are hereby incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0004]     Certain embodiments of the invention relate to processing of video signals. More specifically, certain embodiments of the invention relate to a method and system for 3D comb synchronization and alignment of standard and non-standard video signals.  
       BACKGROUND OF THE INVENTION  
       [0005]     In video system applications, a picture is displayed on a television or computer screen by scanning an electrical signal horizontally across the screen one line at a time. The amplitude of the signal at any one point on the line represents the brightness level at that point on the screen. A video frame contains the necessary information from the lines that make up the picture and from the associated synchronization (sync) signals to allow a scanning circuit to trace the lines from left to right and from top to bottom in order to recreate the picture on the screen. This information includes the luma (Y), or brightness, and the chroma (C), or color, components of the picture. There may be two different types of picture scanning in a video system. The scanning may be interlaced or it may be non-interlaced or progressive. Interlaced scanning occurs when each frame is divided into two separate sub-pictures or fields. The interlaced picture may be produced by first scanning the horizontal lines that correspond to the first field and then retracing to the top of the screen and scanning the horizontal lines that correspond to the second field. The progressive or non-interlaced picture may be produced by scanning all of the horizontal lines of a frame in one pass from the top to the bottom of the screen.  
         [0006]     The luma (Y) and chroma (C) signal components that represent a picture are modulated together in order to generate a composite video signal. Integrating the luma and chroma video elements into a composite video stream facilitates video signal processing since only a single composite video stream is transmitted. Once a composite signal is received, the luma and chroma signal components must be separated in order for the video signal to be processed and displayed as a picture on the screen. A comb filter may be utilized for separating the luma and chroma video signal components. For example, a television may be adapted to receive a composite video input but the chroma and luma video components have to be separated before the television can display the received video signal.  
         [0007]      FIG. 1A  is a diagram illustrating the generation of a conventional composite video signal. Referring to  FIG. 1A , adding the chroma signal component  102  and the luma signal component  104  produces a composite video signal  106 . The luma signal component  104  may or may not increase in amplitude in a stair step fashion. The chroma signal component  102  may comprise a color difference component U that is modulated by, for example, a sine signal with a 3.58 MHz frequency, and a color difference component V that is modulated by, for example, a cosine signal with a 3.58 MHz frequency. The modulation scheme may be selected so that it provides quadrature modulation between the U and V color difference components. An exemplary composite video signal  106  may be a composite video signal with burst and syncs (CVBS).  
         [0008]      FIG. 1B  is a diagram illustrating the position of color burst and active video in a conventional composite video signal. Referring to  FIG. 1B , a portion of the composite video signal  108  may be a color burst  110  and a different portion may be the active video signal  112 . The color burst  110  may comprise a brief sample of, for example, eight to ten cycles of unmodulated color subcarrier which have been inserted by an NTSC or PAL encoder onto the back porch of the composite video signal to enable a decoder to regenerate the color subcarrier from it. The active video portion  112  of the composite video signal  108  contains the luma and chroma signal components of the picture or image.  
         [0009]      FIG. 1C  is a graphical diagram illustrating the phase relationship of modulated chroma signals in contiguous composite video signal frames. The chroma signal component in the active video portion of an NTSC composite video signal may modulated at such a frequency that every line of video in a video frame is phase-shifted by 180 degrees from the previous line. Referring to  FIG. 1C , the bottom frame, the current frame, and the top frame are contiguous composite video frames and the (M−1) video line, the M video line, and the (M+1) video lines are contiguous video lines within the video frame, where M corresponds to any current line which may have a previous line and a next line adjacent to it. The “bottom frame” may correspond to the frame that is currently being received while the “current frame” and the “top frame” may correspond to frames that have been delayed by one and two frames respectively. The M video line in the “current frame” is phase-shifted by 180 degrees from the (M−1) video line in the “current frame” as well as from the (M+1) video line in the “current frame.” Similarly, the M video line in the “bottom frame” is phase-shifted by 180 degrees from the (M−1) video line in the “bottom frame” as well as from the (M+1) video line in the “bottom frame.” In addition, since the fields are at a frequency rate of 59.94 Hz, there is a 180-degree phase shift between two adjacent frames, for example, the “current frame” and the “top frame.” Correspondingly, the M video line in the “current frame” is 180 degrees phase-shifted from the M video line in the “top frame.” In a PAL composite video signal, adjacent video lines and adjacent frames may have a 90-degree phase shift, requiring a two line or two frame delay in order to obtain video lines or frames with a 180-degree phase shift.  
         [0010]     In conventional video processing, there are three ways to separate the luma and chroma video components received in a composite video signal—by utilizing a notch filter, by combing vertically or by combing temporally. During separation of the luma and chroma signal components, there are three bandwidth directions that may incur losses in the separation process and in the separated signal. Depending on the combing method that is utilized, the separated signal may have reduced vertical bandwidth, horizontal bandwidth, and/or temporal bandwidth.  
         [0011]     The first way to separate the luma and chroma video components is by utilizing a notch filter. Since the components in a chroma signal are modulated at 3.58 MHz, a notch filter that is set at 3.58 MHz may be utilized. The notch filter, however, reduces the horizontal bandwidth in the output video signal and as a result the luma video component is increased. A comb filter delays a prior horizontally scanned line in order it compare it with a currently scanned horizontal line. Combing vertically may also be utilized to separate the luma and chroma video components. Combing vertically may be achieved in three different ways—the current line may be combed with the previous and the next line, the current line may be combed with the line just before it, or the current line may be combed with the line just after it. The vertical combing is performed spatially, i.e., only within two fields at a time and without any temporal combing. During combing in the “current frame,” for example, if the current line is added to the previous line, the chroma content cancels out and two times the luma content is obtained. On the other hand, if the previous line is subtracted from the current line, the luma content cancels out and two times the chroma content is obtained. In this way, luma and chroma content may be separated from the composite video signal for further processing. In addition, the vertical combing results in a reduced vertical bandwidth.  
         [0012]     A third way to comb a composite signal is to comb temporally. Combing temporally comprises combing between two adjacent or contiguous frames, for example, the “current frame” and the “bottom frame” or the “current frame” and the “top frame.” Further, temporal combing is characterized by a reduced temporal bandwidth. The luma and chroma components may be separated by utilizing the same addition and subtraction methodology between a current line and a previous line, which is employed by vertical combing.  
         [0013]     While 2-D comb filters may be adapted to process successive scan lines for a single field of a video frame, 3-D comb filters may be adapted to process scan lines that are taken from successive video frames. In general, for 3-D comb filtering, if there is motion between the successive video frames, a 3-D comb filter must revert to 2-D comb filtering. Motion includes color changes and image movement between frames. Accordingly, the 3-D comb filter may be required to buffer at least one frame in order to determine whether there is motion between the buffered frames. In an instance where there are color changes or image movements between the buffered frames, the corresponding Y/C components for the buffered frames will be different and the results of combing would be incorrect.  
         [0014]     Since the 3-D comb filter may be required to buffer at least one frame of video data, several complete frames of video data must be stored in buffers as opposed to just 2 or 3 lines which are required by 2-D comb filters. Accordingly, 3-D comb filters require a large or significant amount of video memory and excessive memory processing bandwidth requirements. This large memory and excessive memory processing bandwidth requirements, along with the necessary motion detection processing, increases the cost associated with 3-D comb filter solutions.  
         [0015]     Three-dimensional (3D) combing algorithms typically operate on video samples that are temporally separated by a video frame, for example, the bottom frame, the current frame, and the top frame in  FIG. 1C . These temporally separated video samples or video frames must be exactly aligned in order to prevent the formation of artifacts in the displayed picture due to misalignment. Alignment of the temporally separated video frames is generally achieved by delaying the frames. The amount of the delay required to align these frames generally varies depending on the video processing standard and/or processing scheme employed. For example, the amount of delay system required for NTSC and PAL standards and for progressive scan input video may vary between the standards. Furthermore, although some signals may conform in some respects to a particular standard, these signals may vary outside the specified ranges permitted by the particular standard. These signals that vary outside the specified ranges permitted by the standard may be referred to as non-standard signals. For example, a non-standard signal, which may be part of a data stream, may have frame lengths that vary outside the ranges permitted by a specific standard or these signals in the data stream may violate the relationship between a specified line length and the subcarrier frequency.  
         [0016]     Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0017]     Certain embodiments of the invention may be found in a method and system for 3D comb synchronization and alignment of standard and non-standard video signals. Aspects of the method comprise coarsely synchronizing and finely aligning a bottom frame, a current frame, and a top frame for video combing. A plurality of bottom frames may be stored prior to coarse synchronization. The stored bottom frames may be standard video frames, non-standard video frames, or compressed video frames. Each field in the bottom frames may be labeled with a bottom frame field count value when a bottom frame vertical sync signal is asserted and with an indication of the location of the bottom frame vertical sync signal. The bottom frame field count may be a modulo N count that is incremented with each assertion of the bottom frame vertical sync signal. The modulo number N may be larger than the total number of fields that may be assigned to the current frame and to the top frame.  
         [0018]     The current frame may be assigned a first frame transferred immediately prior to a bottom frame or a first field and a second field transferred immediately prior to the bottom frame. The current frame and the bottom frame may be locked, or coarsely synchronized, when the bottom frame vertical sync signal occurs within a current frame window signal. The top frame may be assigned a frame transferred two frames prior to the bottom frame or a third field and a fourth field transferred prior to the bottom frame. The top frame and the bottom frame may be locked, or coarsely synchronized, when the bottom frame vertical sync signal occurs within a top frame window signal. Coarse synchronization may result in at least two frames being synchronized to within one subcarrier period. The bottom frame starting field may be utilized as a reference to determine the video fields that may be assigned to the current frame, the top frame, and the bottom frame.  
         [0019]     Fine alignment between the current frame and the bottom frame may comprise correlating a phase difference between a subcarrier signal in the coarsely synchronized current frame and a subcarrier signal in the bottom frame and modifying the phase difference between the frames until the correlation results in a specified phase lock value range. Similarly, fine alignment between the current frame and the top frame may comprise correlating a phase difference between a subcarrier signal in the coarsely synchronized current frame and a subcarrier signal in the coarsely synchronized top frame and modifying the phase difference between the frames until the correlation results in a specified phase lock value range. The specified phase lock value range may correspond to the level of alignment accuracy that may be achieved. The fine frame alignment may result in the addition or removal of an integer sample delay when an integer sample delay slip occurs.  
         [0020]     Aspects of system for synchronization and alignment of standard and non-standard video signals comprise a coarse frame synchronizer that coarsely synchronizes and a fine frame aligner that finely aligns a bottom frame, a current frame, and a top frame for video combing. A plurality of bottom frames may be stored into a memory prior to coarse synchronization. The bottom frames stored may be standard video frames, non-standard video frames, or compressed video frames. A processor may label each field in the bottom frames with a bottom frame field count value when a bottom frame vertical sync signal is asserted and with an indication of the location of the bottom frame vertical sync signal. The bottom frame field count may be a modulo N count that is incremented with each assertion of the bottom frame vertical sync signal. The modulo N number may be larger than the total number of fields that may be assigned to the current frame and to the top frame.  
         [0021]     The processor may assign to the current frame a frame transferred immediately prior to a bottom frame or a first field and a second field transferred immediately prior to the bottom frame. The coarse frame synchronizer may generate a current frame window signal and a top frame window signal. The current frame and the bottom frame may be locked by the coarse frame synchronizer when the bottom frame vertical sync signal occurs within the current frame window signal. The processor may assign to the top frame, a frame transferred two frames prior to the bottom frame or a third field and a fourth field transferred prior to the bottom frame. The top frame and the bottom frame may be locked by the coarse frame synchronizer when the bottom frame vertical sync signal occurs within the top frame window signal. The coarse frame synchronizer may synchronize at least two frames being synchronized to within two integer sample delays. The bottom frame starting field may be utilized as a reference to determine the video fields that may be assigned to the current frame, the top frame, and the bottom frame.  
         [0022]     A fine frame aligner may correlate a phase difference between a subcarrier signal in the coarsely synchronized current frame and a subcarrier signal in the bottom frame and may modify the phase difference between the frames until the correlation results in a specified phase lock value range. Similarly, the fine frame aligner may correlate a phase difference between a subcarrier signal in the coarsely synchronized current frame and a subcarrier signal in the coarsely synchronized top frame and may modify the phase difference between the frames until the correlation results in a specified phase lock value range. The specified phase lock value range may correspond the level of alignment accuracy that may be achieved and may be specified by the processor. The fine frame aligner may add or remove an integer sample delay when an integer sample delay slip occurs.  
         [0023]     These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.  
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0024]      FIG. 1A  is a diagram illustrating the generation of a conventional composite video signal.  
         [0025]      FIG. 1B  is a diagram illustrating the position of color burst and active video in a conventional composite video signal.  
         [0026]      FIG. 1C  is a graphical diagram illustrating the phase relationship of modulated chroma signals in contiguous composite video signal frames.  
         [0027]      FIG. 2  is a block diagram illustrating an exemplary system which may be utilized for 3D comb synchronization and alignment of standard and non-standard video signals, in accordance with an embodiment of the invention.  
         [0028]      FIG. 3  is an exemplary timing diagram illustrating coarse synchronization between the bottom frame, the current frame, and the top frame for interlaced video signals, in accordance with an embodiment of the invention.  
         [0029]      FIG. 4  is a flow diagram illustrating exemplary steps which may be utilized for coarse synchronization between the bottom frame, the current frame, and the top frame, in accordance with an embodiment of the invention.  
         [0030]      FIG. 5  is a block diagram of an exemplary fine frame synchronizer which may be utilized for fine synchronization between the bottom frame, the current frame, and the top frame, in accordance with an embodiment of the invention.  
         [0031]      FIG. 6  is a flow diagram illustrating exemplary steps which may be utilized for fine synchronization between the current frame, the bottom frame, and the top frame, in accordance with an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     Certain aspects of the invention may be found in a method and system for 3D comb synchronization and alignment of standard and non-standard video signals. Aspects of the invention may facilitate the handling of video stream switching and non-standard data streams. Video stream switching may occur, for example, when a television channel is changed, thereby causing the video stream to also change. The handling of video stream switching and the handling of the non-standard data streams may be accomplished in an organized manner by, for example, appropriately labeling and storing the video stream, followed by a coarse synchronization and then by a fine alignment of the stored video fields and/or video frames.  
         [0033]      FIG. 2  is a block diagram illustrating an exemplary system which may be utilized for 3D comb synchronization and alignment of standard and non-standard video signals, in accordance with an embodiment of the invention. Referring to  FIG. 2 , the synchronization and alignment system  200  may comprise a coarse frame synchronizer  202 , a fine frame aligner  204 , a processor  206 , and a memory  208 . The coarse frame synchronizer may comprise suitable logic, code, and/or circuitry and may be adapted to coarsely synchronize a current frame with a bottom frame and/or a top frame with the bottom frame to within one subcarrier period. The fine frame aligner  204  may comprise suitable logic, code, and/or circuitry and may be adapted to finely align the top frame with the current frame and/or the bottom frame with the current frame to within a specified phase lock value range. The processor  206  may comprise suitable logic, code, and/or circuitry and may be adapted to control the operation of the coarse frame synchronizer  202  and the fine frame aligner  204 , and to transfer control information and/or data between the memory  208  and the coarse frame synchronizer  202  and the fine frame aligner  204 . The memory  208  may comprise suitable logic, code, and/or circuitry and may be adapted to store control information and/or data for use by the synchronization and alignment system  200 .  
         [0034]      FIG. 3  is an exemplary timing diagram illustrating an exemplary coarse synchronization between the bottom frame, the current frame, and the top frame for interlaced video signals, in accordance with an embodiment of the invention. Referring to  FIG. 3 , timing signals that may be utilized by the coarse frame synchronizer  202  for coarse synchronization in interlaced video signals may comprise a bottom frame vertical sync (VW) signal  302 , a bottom frame field count (FC) signal  304 , a current frame state (CFS) signal  306 , a current frame window (CFW) signal  308 , a top frame state (TFS) signal  310 , and a top frame window (TFW) signal  312 . The VW signal  302  may correspond to the clock assertion of a vertical sync signal which indicates the presence of a video field in a bottom frame video stream from the memory  208 . The FC signal  304  may correspond to the count value in a modulo N counter indicating the order of arrival of a new video field in the bottom frame video stream. The CFS signal  406  may correspond to the status of the current frame relative to a bottom frame starting field. The CFW signal  308  may correspond to a time interval during which confirmation of coarse synchronization between the current frame and the bottom frame may be determined. The TFS signal  310  may correspond to the status of the top frame relative to the bottom frame starting field. The TFW signal  312  may correspond to a time interval during which confirmation of coarse synchronization between the top frame and the bottom frame may be determined.  
         [0035]     At time t 0  in the timing diagram, the bottom frame, the current frame, and the top frame are not locked or coarsely synchronized. The time in  FIG. 3  increases from left to right. When the VW signal  302 , also known as V-Write signal, is asserted, the FC signal  304  is incremented to indicate the presence of a new bottom frame video field. The FC signal  304  is incremented after every new video field in the bottom frame video stream until it reaches its maximum value, as determined by the modulo N count, at which point the next FC signal  304  value is 0. The number N may be based on the ability to track the number of video field delays that exist between the top frame and the bottom frame. The bottom frame starting field may be, for example, the video field in the bottom frame video stream in  FIG. 3  that corresponds to an FC signal  304  of value 0. The bottom frame starting field may be used as a reference to determine the video fields that may correspond to the top frame, the current frame, and the bottom frame. For example, when the bottom frame starting field in  FIG. 3  corresponds to the FC signal  304  value of 0, then it may be delayed by two fields from the bottom frame video field that corresponds to an FC signal  304  value of 2 and by four fields from the bottom frame video field that corresponds to an FC signal  304  value of 4. When the bottom frame comprises the bottom frame video fields that corresponds to FC signal  304  values 5 and 4, then the current field may comprise the bottom frame video fields that correspond to FC signal  304  values 3 and 2 and the top frame may comprise the bottom frame video fields that correspond to FC signal  304  values 1 and 0. Similarly, when the bottom frame comprises the bottom frame video fields that corresponds to FC signal  304  values 6 and 5, then the current field may comprise the bottom frame video fields that correspond to FC signal  304  values 4 and 3 and the top frame may comprise the bottom frame video fields that correspond to FC signal  304  values 2 and 1. The bottom frame may comprise the most recent video fields received from the bottom frame video stream by the coarse frame synchronizer  202 .  
         [0036]     The CFS signal  306  may be utilized to indicate whether the coarse frame synchronizer  202  has read the bottom frame starting field from the memory  208 . The CFS signal  306  may also be utilized to indicate that, after the bottom frame starting field has been read at time t 1 , the coarse frame synchronizer  202  is reading additional video fields from the memory  208 . The CFS signal  306  may be utilized to confirm, at time t 3 , that the video fields necessary to assemble the current frame have been read from the memory  208  and that they are now locked, at time t 4 , to the VW signal  302 . The CFW signal  308  may be generated by the coarse frame synchronizer  202  during confirmation of the current frame in the CFS signal  306  and may be used by the CFS signal  306  to determine whether the current frame is coarsely synchronized.  
         [0037]     The TFS signal  310  may be used to indicate whether the coarse frame synchronizer  202  has read the bottom frame starting field from the memory  208 . The TFS signal  310  may also indicate that, after the bottom frame starting field has been read at time t 1 , the coarse frame synchronizer  202  is reading additional video fields from the memory  208  and that those additional video fields may be delayed by the appropriate amount, for example, at time t 5 . The TFS signal  310  may confirm, at time t 6 , that the video fields necessary to assemble the top frame have been read from the memory  208  and that they are now locked, at time t 7 , to the VW signal  302 . The TFW signal  312  may be generated by the coarse frame synchronizer  202  during confirmation of the top frame in the TFS signal  310  and may be used by the TFS signal  310  to determine whether the top frame is coarsely synchronized.  
         [0038]     The timing signals that may be utilized by the coarse frame synchronizer  202  for coarse synchronization in interlaced video signals may also be used for progressive video signals when the progressive video signals have an odd number of lines.  
         [0039]      FIG. 4  is a flow diagram illustrating exemplary steps which may be utilized for coarse synchronization between the bottom frame, the current frame, and the top frame, in accordance with an embodiment of the invention. Referring to  FIG. 4 , after start step  402 , in step  404  the synchronization and alignment system  200  stores and labels the bottom frames in the bottom frame video stream continuously into the memory  208 . The labeling may indicate the field count value and/or the location of the vertical sync signal. In an interlaced system the field count corresponds to a bottom frame field count while in a progressive system the field count corresponds to a bottom frame count. In step  406 , after the assertion of the VW signal, the current frame and top frame read pointers may be adjusted to correspond to the bottom frame starting field or the bottom frame starting frame. In step  408 , the coarse frame synchronizer  202  may read from the memory  208  the labeled bottom frame fields or bottom frames depending on whether the system is interlaced or progressive. In step  410 , the coarse frame synchronizer  202  determines whether the fields or frames read correspond to the bottom frame starting field or a bottom frame starting frame for progressive systems. If the field or frame which has been read does not correspond to the bottom frame starting field or to the bottom frame starting frame, then the coarse frame synchronizer returns to step  406  and adjusts the current frame and top frame pointers. If the field or frame which has been read does correspond to the bottom frame starting field or to the bottom frame starting frame, then the coarse frame synchronizer may proceed to step  412  to coarsely synchronize the current frame with the bottom frame and/or to step  420  to coarsely synchronize the top frame with the bottom frame.  
         [0040]     In step  412 , after having read the bottom frame starting field or the bottom frame starting frame, the coarse frame synchronizer  202  waits for the appropriate number of fields or frames to be read. Once the appropriate fields or frame are delayed that may correspond to the current frame, the coarse frame synchronizer  202  may assign the fields or frame to the current frame. In step  414 , after the current frame has been completed, the coarse frame synchronizer  202  may generate the current frame window (CFW) signal to confirm synchronization between the current frame and the bottom frame.  
         [0041]     In step  416 , the coarse frame synchronizer  202  may determine whether the current frame and the bottom frame are coarsely synchronized by comparing the VW signal and the CFW signal. If the VW signal occurs within the duration of the CFW signal, the current frame and the bottom frame are coarsely synchronized and the coarse frame synchronizer may proceed to step  418 . If the VW signal does not occur within the duration of the CFW, then the current frame and the bottom frame are not coarsely synchronized and the coarse frame synchronizer  202  may return to step  406  and start the process again. In step  418 , the coarse frame synchronizer  202  may indicate in the current frame state (CFS) signal that the current frame and the bottom frame are locked. Coarse synchronization may bring the current frame and bottom frame to within one subcarrier period. Once the frames are locked, the synchronization and alignment system  200  may proceed to step  428  where the bottom frame, the current frame, and the top frame may be finely aligned.  
         [0042]     Returning to step  420 , after having read the bottom frame starting field or the bottom frame starting frame, the coarse frame synchronizer  202  waits for the appropriate number of fields or frames to be read. Once the appropriate fields or frame are delayed that may correspond to the top frame, the coarse frame synchronizer  202  may assign the fields or frames to the top frame. In step  422 , after the top frame has been completed, the coarse frame synchronizer  202  may generate the top frame window (TFW) signal to confirm synchronization between the top frame and the bottom frame.  
         [0043]     In step  424 , the coarse frame synchronizer  202  may determine whether the top frame and the bottom frame are coarsely synchronized by comparing the VW signal and the TFW signal. If the VW signal occurs within the duration of the TFW signal, the top frame and the bottom frame are coarsely synchronized and the coarse frame synchronizer may proceed to step  426 . If the VW signal does not occur within the duration of the TFW, then the top frame and the bottom frame are not coarsely synchronized and the coarse frame synchronizer  202  may return to step  406  and start the process again. In step  426 , the coarse frame synchronizer  202  may indicate in the top frame state (TFS) signal that the top frame and the bottom frame are locked. Coarse synchronization may bring the top frame and bottom frame to within one subcarrier period. Once the frames are locked, the synchronization and alignment system  200  may proceed to step  428  where the bottom frame, the current frame, and the top frame may be finely aligned.  
         [0044]      FIG. 5  is a block diagram of an exemplary fine frame synchronizer which may be utilized for fine synchronization between the bottom frame, the current frame, and the top frame, in accordance with an embodiment of the invention. Referring to  FIG. 5 , the fine frame aligner  204  may comprise a fixed integer delay  502 ,  504 , a matching delay  506 , an integer slip  508 ,  510 , a FSA filter  512 ,  514 , a bottom frame subcarrier lock loop  516 , and a top frame subcarrier lock loop  518 . The bottom frame subcarrier lock loop may comprise a filter  520 , for example, a Hilbert filter, a correlator  522 , a low pass filter  524 , and a loop filter  526 . The top frame subcarrier lock loop may comprise a filter  528 , for example, a Hilbert filter, a correlator  530 , a low pass filter  532 , and a loop filter  534 .  
         [0045]     The fixed integer delay  502 ,  504  may comprise suitable logic, code, and/or circuitry and may be adapted to provide integer sample delays for the current frame and for the top frame in fixed clock architectures. For example, the sample delays may be based on an integer sample from a 27 MHz clock. The matching delay  506  may comprise suitable logic, code, and/or circuitry and may be adapted to adjust the delay for the current frame in fixed clock architectures. The integer slip  508 ,  510  may comprise suitable logic, code, and/or circuitry and may be adapted to add or remove an integer sample delay when the fractional delay crosses an integer boundary. The FSA filter  512 ,  514  may comprise suitable logic, code, and/or circuitry and may be adapted to determine the amount of fractional delay to apply to the bottom frame and for the top frame. The bottom frame subcarrier lock loop  516  may comprise suitable logic, code, and/or circuitry and may be adapted to lock the subcarrier signals in the current frame and the bottom frame. The top frame subcarrier lock loop  518  may comprise suitable logic, code, and/or circuitry and may be adapted to lock the subcarrier signals in the current frame and the top frame.  
         [0046]     The Hilbert filter  520  in the bottom frame subcarrier lock loop  516  may comprise suitable logic, code, and/or circuitry and may be adapted to shift the subcarrier phase in the color burst of the signal coming from the FSA filter  512  by 90°. The correlator  522  may comprise suitable logic, code, and/or circuitry and may be adapted to correlate the color burst subcarrier of the signal coming from the Hilbert filter  520  and the color burst subcarrier of the current frame. The low pass filter  524  may comprise suitable logic, code, and/or circuitry and may be adapted to remove higher level harmonics that may result from the operation of the correlator  522 . The loop filter  526  may comprise suitable logic, code, and/or circuitry and may be adapted to control the feedback rate in the bottom frame subcarrier lock loop  516 .  
         [0047]     The Hilbert filter  528  in the top frame subcarrier lock loop  518  may comprise suitable logic, code, and/or circuitry and may be adapted to shift the subcarrier phase in the color burst of the signal coming from the FSA filter  514  by 90°. The correlator  530  may comprise suitable logic, code, and/or circuitry and may be adapted to correlate the color burst subcarrier of the signal coming from the Hilbert filter  528  and the color burst subcarrier of the current frame. The low pass filter  532  may comprise suitable logic, code, and/or circuitry and may be adapted to remove higher level harmonics that may result from the operation of the correlator  530 . The loop filter  534  may comprise suitable logic, code, and/or circuitry and may be adapted to control the feedback rate in the top frame subcarrier lock loop  518 .  
         [0048]      FIG. 6  is a flow diagram illustrating exemplary steps which may be utilized for fine synchronization between the current frame, the bottom frame, and the top frame, in accordance with an embodiment of the invention. Referring to  FIG. 6 , after start step  602 , the integer slip  508 ,  510  may determine, in step  604 , whether the coarsely synchronized bottom frame and/or the coarsely synchronized top frame may require the addition or removal of an integer sample delay. If an integer sample delay may not need to be added or removed, the bottom frame and/or the top frame in the fine frame aligner  204  may proceed to step  608 . In step  608 , the FSA filter  512 ,  514  may adjust a fractional delay to the bottom frame and/or the top frame respectively if the feedback from the bottom frame subcarrier lock loop  516  and the top frame subcarrier lock loop  518  provides for the adjustment.  
         [0049]     In step  610 , the Hilbert filter  520 ,  528  may apply a 90 phase shift to the color burst subcarrier in the bottom frame and/or the top frame. In step  612 , the correlator  522 ,  530  may correlate the color burst subcarrier of the bottom frame and top frame respectively with the color burst subcarrier of the current frame. The correlation in step  612  may correspond to an error signal between the color burst subcarrier phase of the current frame and the color burst subcarrier phase of the bottom frame and/or the top frame. In step  614 , the subcarrier phase error produced by the correlator  522 ,  530  may be low pass filtered to remove any higher order harmonics. In step  616 , the low pass filtered subcarrier phase error from step  614  may be applied to the loop filter  526 ,  534  to determine feedback rate at which the subcarrier phase error may be applied to the integer slip  508 ,  510  and/or the FSA filter  512 ,  514 . In step  618 , the loop filter  526 ,  534  may determine whether the subcarrier phase error is within a specified phase lock value range. The specified phase lock value range may be programmed by the processor  206  and may be determined based on systems requirements. If the subcarrier phase error is not within the specified phase lock value range, then the fine frame aligner  204  may return to step  604  and provide the subcarrier phase error to the integer slip  508 ,  510  and/or it may return to step  608  and provide the subcarrier phase error to the FSA filter  512 ,  514  at the feedback rate determined in step  616 . Whether the fine frame aligner  204  returns to step  604  or to step  608  may depend on the need for an integer slip in the feedback loop.  
         [0050]     Returning to step  604 , when the feedback provided by the bottom frame subcarrier lock loop  516  and/or the top frame subcarrier lock loop  518  produces a fractional delay that crosses an integer boundary, that is, a delay that may be longer than an integer sample delay and that may require an integer slip, the fine frame aligner  204  may add or remove an integer sample delay in step  606  before proceeding to step  608 . In this case, the fractional delay applied in step  608  may be adjusted to reflect the integer slip that may have taken place in step  606 .  
         [0051]     Returning to step  618 , if the subcarrier phase error is within the specified phase lock value range, then the fine frame aligner may proceed to step  620  where the bottom frame and/or the top frame may be considered to be finely aligned with the current frame.  
         [0052]     Accordingly, the present invention may be realized in hardware, software, or a combination of hardware and software. The present invention may be realized in a centralized fashion in at least one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may be a general-purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.  
         [0053]     The present invention may also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context means any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.  
         [0054]     While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiment disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.