PATENT ABSTRACT
A digital recording device for storing video data is disclosed. The digital recorder intelligently records less data than is provided to it by determining which data to record, and which data to eliminate. In some embodiments, the recorder drops or modifies overscan data from a video frame prior to compressing the data, thereby relieving a data encoder from unnecessary data operations, and saving storage space.

PATENT DESCRIPTION
TECHNICAL FIELD 
   This disclosure relates to personal video recording systems and, more particularly, to a personal video recording system that can record less than the full amount of a video signal provided to it. 
   BACKGROUND 
   Personal video recording devices (PVRs) are becoming more commonplace in society. Like Video Cassette Recorders (VCRs), PVRs store video signals for later retrieval and reproduction, thereby allowing users to record a program that is broadcast at one time and view it at another time (time shifting). However, PVRs differ from VCRs in many ways. 
   One major difference is that, whereas VCRs store video signals on inexpensive magnetic tapes, PVRs store encoded video signals on a magnetic hard disk or hard drive. When a user wishes to watch a previously stored video program, the encoded data is retrieved from the hard drive, decoded, and then rendered on a television (TV) or monitor. 
   One set of problems with current PVRs revolve around storing the data on the hard drive. Unlike VCRs, where inexpensive tapes used to store the programs are easily removable, the hard drive is, to the typical user, permanently fixed within the PVR. The hard drive has a finite storage capacity, and therefore so too does the PVR. Once the hard drive is filled with data, no additional data can be stored until some of the data on the drive is deleted. Present PVRs lack any mechanism to easily transmit the data outside of the system, such as to a tape or removable disk. Therefore, data deleted from the hard drive is permanently lost, unless the data is re-captured from a different broadcast and again stored on the hard drive. 
   As PVRs evolve, users would like to see additional capability and functionality in their systems. For instance, a PVR that included multiple input data channels could record multiple channels of programming at the same time. Additionally, quality of the reproduced video could be enhanced if more data could be stored on the hard drive. There are ever increasing demands for storing more data at a faster rate with higher quality on a PVR. 
   Presently, data throughput of the hard drive is one of the system parameters that is most strongly considered when designing a PVR. The hard drive of the PVR has a finite input/output (throughput) bandwidth. If the throughput bandwidth could be raised, the amount of data simultaneously stored on the hard drive could be increased, and the quality of the compressed image data stored on the hard drive could be improved. Unfortunately, the throughput capacity of hard drives is fixed by hardware constraints of the drives themselves, and cannot be easily modified above their current maximum. 
   Embodiments of the invention address these and other deficiencies. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description may be best understood by reading the disclosure with reference to the drawings, wherein: 
       FIG. 1  is a functional block diagram of a Personal Video Recorder system according to embodiments of the invention. 
       FIG. 2  is a diagram of video frame including overscan areas. 
       FIG. 3  is an example flow diagram showing processes perform by the Personal Video Recorder of  FIG. 1 . 
       FIG. 4  is a diagram showing how blocks are arranged within an image frame. 
       FIGS. 5A ,  5 B, and  5 C are example flow diagrams showing additional detail to the process illustrated in  FIG. 3 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a functional block diagram of a PVR system  5 , according to embodiments of the invention. The PVR system  5  includes a tuner  10  that provides a tuned video/audio signal, such as a channel of broadcast, cable, or satellite television. An analog to digital converter (not shown) is present in either the tuner  10  or a capture device  15 , and is used to convert the analog video and audio signals into a stream of digital data signals. 
   The capture device  15  accepts the data stream from the tuner  10  and breaks the data stream into manageable chunks of data. The data chunks are oftentimes sized to include one or two fields. In TV displays, generally, two fields make up a single frame or image, which is updated between 24 and 60 times per second. On TVs, the two fields are typically shown in an interlaced format, with each field displaying on every other line of a screen of a TV. When superimposed, the two fields create the complete image frame. Computer monitors, conversely, generally display the two fields in a non-interlaced format, where the fields are combined in a frame prior to being shown, and the frame shown at one time. In describing embodiments of the invention, data groupings will be referred to as “frames”, although embodiments are able to work equally as well with either frames or fields as the group of data output by the capture device  15 . 
   The captured frames are passed from the capture device  15  to a video encoder  20 , such as an MPEG (Moving Picture Experts Group) encoder. Other types of encoders are possible, such as MJPEG (Moving Joint Photographics Expert Group), and those using streaming formats such as REAL MEDIA, WINDOWS MEDIA, or QUICKTIME. Embodiments of the invention are able to work with any of these formats, and others. Audio data corresponding to the video frames are passed to an audio encoder  25  that operates in conjunction with the selected video encoder format. After encoding, the encoded video and audio signals are stored on a storage device  30 . Typically a computer hard drive serves as the storage device  30 , because a hard drive provides a relatively inexpensive and efficient way to store large amounts of digital data. 
   To view the stored video data, first the data is retrieved from the storage device  30  and passed to a set of video and audio decoders  40 ,  45  which use the retrieved data to re-create the desired image fields or frames. Of course, the video and audio decoders  40 ,  45  are matched so that they can decode whatever format was used for the video and audio encoding. The re-created frames are then sent to a rendering device  50  for display and playback on a TV or monitor  60 . Such a PVR system  5  allows the user to record programs, store them on the hard drive  30 , and play them back at the user&#39;s direction. 
   The PVR system  5  of  FIG. 1  differs from standard PVRs, however, in that it can modify the video signal between the time it is received from the tuner  10  and the time it is rendered on a TV or monitor  60 . Plus, this modification can be performed so that the modification is completely or nearly completely unnoticeable to a viewer of the re-created image. Specifically, embodiments of the invention capture, encode, decode, and/or render less than a full frame of image data. By processing less than all of the data sent to the PVR system  5 , embodiments of the invention are able to store more data, and store it faster, than other PVRs not so configured, without causing a degradation in picture quality. 
   These embodiments process less than the entire amount of data by deleting, manipulating or otherwise treating data contained in an overscan region of the image frame differently than data contained in the central, or non-overscan region. The overscan region of an image frame makes up the outermost portions of the image frame, as described with reference to  FIG. 2 . 
     FIG. 2  shows a full image frame  8  and a smaller image frame  12  that is roughly 95% the size of the frame  8 . The image frame  8  is the entire frame that would be output from a standard capture device. In nearly every consumer TV, only a central image area  18 , bounded by the smaller image frame  12  is actually displayed to a viewer, and not the full image frame  8 . In other words, an overscan area  13 , located between the image frames  8  and  12 , is typically not visible to the TV viewers. 
   Frames  8  can be of any size, but there are some typical or standard sizes used in industry. For instance, the outermost portion of the frame  8  may have a size of 352 pixels in height and 480 pixels in width. This is commonly referred to as 352×480. Other standard sizes include 480×480, 512×480 and 640×480. It is common to characterize the size of a frame in discrete pixel sizes, even though the actual signal input into the tuner  10  of the PVR system  5  ( FIG. 1 ) is analog, and the output display  60  is typically an analog TV. Oftentimes, the resolution of a TV is stated as lines of resolution, such as 525 or 480, but the pixel size of the frame need not, and probably will not, necessarily match the TV resolution. 
   Returning back to  FIG. 2 , although the overscan area  13  is not displayed by a TV, the data making up the overscan area is generally still broadcast or otherwise delivered to the TV. Showing only the non-overscan regions, or central image area  18  can be thought of as similar to “cropping” edges of a photograph or placing a mat around a picture. The amount of cropping or overscan varies from one TV to another, but generally at least 5% and possibly up to 15% of the original image frame input to the TV is omitted from the image shown on the TV screen. 
   One reason for TVs having any amount of overscan is that early consumers of televisions did not want to “waste” any of the area of their expensive TV screens, and demanded that the image take up the entire TV screen area. Because the extreme edges of early TV screens produced poor images, manufacturers internally cropped the edges of the phosphor screen in TVs by placing an opaque material over the edges, or by using other methods. Although early TVs produced the entire original signal, the edges were physically blocked from the TV viewer, and viewers only saw the central image area  18 . 
   Broadcasters eventually realized that they were sending portions of images, i.e., the overscan regions  13 , which were never seen by anyone, and, began using the overscan region for other purposes. Presently the overscan region  13  may be used to carry no data, or simple noise data, or even useful information as a “data channel.” For example, Actimates toys use the left-most pixel of the overscan region  13  as a data channel to send data that allows their toys to “interact” with the TV. Similarly, closed captioning in the USA is carried in one of the vertical lines in the overscan region  13 . 
   Typical PVRs capture, encode, store, and decode the entire image frame  8  ( FIG. 2 ) presented to the PVR, while embodiments of the invention minimize processing and storage by treating data in the overscan region  13  of the video signals differently than data in the central image area  18  of the frame  8 . In some embodiments, the overscan region  13  is simply not captured, encoded, stored or decoded. Other embodiments may capture the overscan region  13 , but modify the encoding such that the overscan regions are not coded or stored on the hard drive  30 . Or, the overscan region  13  itself may be modified, such as by changing it to all black pixels prior to encoding. This allows the encoding to proceed much faster than if the original overscan  13  data was also coded. Still other embodiments modify both the coder and decoder to minimize overscan coding and decoding. 
   The following discussion provides details on how the PVR system  5  of  FIG. 1  processes incoming video signals differently than other PVR  5  systems. Some embodiments of the inventive PVR system  5  include a frame modifier  16  located between the capture device  15  and the video encoder  20 . The frame modifier  16  is used to delete portions of or the entire overscan area  13  of a video data frame  8 . In one of the easiest to implement modes of operation, the frame modifier  16  may simply strip data from one or both of the top and bottom margins of the overscan area  13  of the original image frame  8 . In other embodiments, the frame modifier  16  may strip data from all of the top, bottom, left and right margins of the overscan area of the original image frame  8 . This latter embodiment is more difficult to implement because the data input into the capture device  15  is typically in rasterized format, i.e. the input data is streamed as if it were a single dimension array of data, and not broken into lines or blocks of the image frame  8 . This can be especially difficult if the data is presented in interlaced format, in which relative location of data within the data stream does not directly correlate to the location of the data within the image frame  8 . 
   The frame modifier  16  strips the top and bottom lines by simply deleting the data from the beginning and end of the original image frame  8  prior to passing it to the video encoder  20 . Deleting data from the left and right margins of the overscan area  13  is more difficult because the frame modifier  15  must strip some of the data from the beginning and end of each line of the image frame  8 , and allow other data to pass in each line to create the central area  18  of the image frame  8 . 
   In this embodiment, the frame modifier  16  simply deletes an amount of data, preferably between 3% and 15% prior to it ever being encoded by the video encoder  20 . Because less image data is supplied to the video encoder  20 , the video encoder operates on a reduced amount of data and can therefore operate faster than if it were operating on the entire standard image frame  8 . The amount of data from the overscan region  13  discarded or modified by the frame modifier  16  can be determined when the PVR system  5  is designed or implemented. If more data is discarded, the video encoder  20  may operate faster but a viewer may be able to detect that some data of the image is missing. If less data is discarded, the viewer will not detect any missing data, but the savings in encoding time will not be as great. 
   In implementation the frame modifier  16  may be a standalone component or run in firmware or could even be a software process running on a dedicated or general purpose processor. Additionally, the frame modifier  16  may be implemented as part of the capture device  15 , or even as part of the video encoder  20 . 
     FIG. 3  is an example flow diagram showing processing that can occur in the frame modifier  16 . A flow  100  begins at a process  105  where a next block of a current frame is examined. The frame modifier  16  may operate with single lines of image data, but it is more convenient for groups of pixels to be processed in blocks of adjacent pixels, as is known in the art. In MPEG encoding, macroblocks are formed by groups of 16 horizontal pixels and 32 vertical pixels. In embodiments of the invention, the overscan region  13  is chosen to be sized so that it is made of many complete blocks, i.e., a particular block of the frame  8  is either entirely inside or outside the overscan region. 
   For instance, shown in  FIG. 4  is a sample image frame  8  made from 35 macroblocks B 1 -B 35 . The central image area  18 , which is bound by the smaller frame  12 , includes only blocks B 9 -B 13 , B 16 -B 20 , and B 23 -B 27 . The image frame  8  of  FIG. 4  is only illustrative and typically an image frame would be made out of many more macroblocks than  35 ,and the ratio of the number of macroblocks in the central image area  18  to the number of macroblocks in the entire image frame  8  would be much greater than that shown in  FIG. 4 . It is also possible to operate the frame modifier  16  and/or other components of the PVR system  5  in other mode where only a partial block is within the overscan region  13 , but more processing is required, however. 
   Returning back to  FIG. 3 , process  110  analyzes the acquired block, and a check  115  determines if the block is in the border to be modified. If yes, then the block is modified in a process  120 , such as by being deleted or otherwise modified as described below. If the block is not in the border, it is left alone. A check  125  is performed to see if there are more blocks in the frame. If so, the flow  100  repeats until all of the blocks in the entire image frame  8  has been analyzed. 
     FIGS. 5A and 5B  show additional detail of flows for particular implementations of the frame modifier  16 . In a flow  101  of  FIG. 5A , a check  116  is substituted for the check  115  of  FIG. 3  in that the block is analyzed to determine only if it is in the top or the bottom of the overscan region  13 . If so, the block is deleted from the frame in a process  121 . In the implementation illustrated in flow  102  of  FIG. 5B , the block is checked in a process  117  to determine if it is in either the top, bottom, or left or right margins of the overscan region  13  of the current frame. Again, if the block is in such a margin, it is deleted in the process  121 . The remainder of the flows  101  and  102  ( FIGS. 5A and 5B  respectively), are the same as in the flow  100  of  FIG. 3 . 
   One advantage in an embodiment such as explained with reference to  FIGS. 5A and 5B  is that no modifications are necessary to the video encoder  20  or the video decoder  40  from a standard PVR system. This is because, in such systems, the video encoder  20  will simply encode all of the data that is passed to it, and the video decoder  40  will likewise decode all of the data. In this embodiment, without further modification, the actual size of the final image displayed on the TV or monitor  60  ( FIG. 1 ) may be smaller than it would be if the overscan region  13  were not deleted. However, if the frame modifier  16  only deletes a small overscan region  13 , then the displayed image may actually still be within the original borders of what is shown on the monitor  60 , which automatically crops 5% to 10% of all images it receives. Another solution is to cause the rendering device  50  to “zoom” or slightly enlarge the displayed frame so that it takes up the entire standard viewing area on the monitor  60 . 
   Returning back to  FIG. 1 , other embodiments of the inventive PVR system  5  can include an overscan encoder  21  within the video encoder  20 . Similarly, an overscan decoder  41  can be included in the video decoder  40 . The overscan encoder  21  can work independently or can work together with the overscan decoder  41  to minimize the amount of work performed by the video encoder  20  and decoder  40 , as discussed below. 
   In one embodiment, the overscan encoder  21  can operate in a fashion similar to that of the frame modifier  16 . In that embodiment, the overscan encoder  21  modifies the data in the blocks making up the overscan region  13  of the frame  8 , for instance, by changing the color of all of the pixels in the current block to black. Because all of the pixels in the blocks are then the same color, they can be compressed to a great degree by the video encoder  20 . A flow  103  showing this embodiment is illustrated in  FIG. 4C . In that flow, if the check  115  determines that the current block is to be modified, e.g., is in the overscan portion  13  of the current frame  8 , then all of the pixels within that block are turned to black in a process  122 . 
   Another possibility to minimize the coding effort of the encoder  20  is to modify data making up the blocks in the overscan region  13  such that the image frame  8  can be most easily coded by the video encoder. For example, the overscan encoder may scan the current image frame  8  and place data into the blocks of the overscan region  13  that can most easily be compressed, based on the contents of the blocks in the central image area  18  of the current image frame. In some encoders, the data that may make it the easiest for the video encoder  20  to encode may be a simply copy of the data on the outermost blocks of the central portion  18  to the overscan region  13 . That way the video encoder  20  could just make a simple notation that the entire block is repeated in the overscan regions. This embodiment may involve a large amount of pre-processing in order to make the actual video processing by the video encoder  20  easier. The data placed in the overscan area  13  in those embodiments of the invention would depend greatly on the way the video encoder  20  operates, and thus the actual data placed in the overscan area  13  is best determined when the video encoder  20  is implemented. 
   These embodiments where the data in the overscan region  13  is modified (using the overscan encoder  21 ) differ from the ones where the data in the overscan region is simply deleted (using the frame modifier  16 ), because in the latter examples using the overscan encoder  21 , the video encoder  20  still encodes the overscan region  13 . This distinction is highlighted by another embodiment of the video encoder  20  in the PVR system  5  of  FIG. 1 , which operates to simply not code the overscan regions  13 , regardless of what data the blocks making up that region include. In this embodiment, the video encoder  20  ignores the data contained in the overscan region  13  when encoding the video data. 
   Yet other embodiments of the video encoder use a conjunction of the overscan encoder  21  and the overscan decoder  41  to determine the easiest way to minimize coding necessary to produce the central image area  18  of the frame  8 . Such a system is possible because both the video encoder  20  and the video decoder  40  exist within the same system (the PVR system  5  of  FIG. 1 ). In other applications for displaying video, such as a DVD player or a decoder that decodes streaming media, generally an encoder is completely separate from a decoder. For instance a DVD player typically includes only a decoder, while the encoder used to encode a DVD could be a special use encoder used to produce the DVD master. 
   These embodiments where the encoder  20  and decoder  40  cooperate may modify such parameters as motion vectors, in those encoders that use them. The motion vectors may be reduced for blocks in regions near or fully within the overscan region  13 , while the motion vectors for the remainder of the image frame  8  are not reduced. 
   Additionally, many of the methods of reduced overscan coding can work cooperatively. For instance it may be beneficial to both change data in the overscan region  13  to black, and to modify the motion vectors in the encoder  20  in regions near the blacked-out edge, so that the encoder can operate more efficiently. In almost all of the methods described above, the renderer  50  can be adjusted to “zoom” the final display of the shown image such that no borders are visible in the displayed frame. 
   Using reduced overscan coding in PVR devices has advantages over present methods used in conventional PVRs. Because less data is being encoded, the storage device in the PVR can hold more data. This allows the PVR to record more hours of video, providing a desirable benefit to the user. Or, because it is encoding less data, or encoding data more efficiently, the PVR may be able to encode video from more than one source (such as multiple channels) simultaneously. Another advantage is that the encoder may be able to encode at a higher quality, using the same amount of data as is presently used. 
   Implementation of the PVR having reduced overscan coding is straightforward and intuitive once the details of the invention as described above are known. As always, implementation of the invention is left to the system designer. The circuits and processes may be implemented in any way, with any components as long as they can perform the necessary functions. Each of the processes may be integrated with others, or they may operate in a standalone manner. The individual processes described above were explained and shown with regard to their function, rather than to their physical implementation. The processes may operate in specific hardware, firmware, or could be software processes running on special or general purpose processors. 
   Thus, although particular embodiments for a PVR having reduced overscan coding have been discussed, it is not intended that such specific references be considered as limitations upon the scope of this invention, but rather the scope is determined by the following claims and their equivalents.