Method and Apparatus for Common Vertical Blanking Interval Scan Line Decoding

1. Field of the Invention

The present invention relates to the field of television signal processing. More specifically, the present invention relates to the capturing and decoding of vertical blanking interval (VBI) scan lines.

2. Background Information

Broadcasting of closed captions, teletext, etc. in the vertical blank intervals of television signals is known in the art. Conventionally, capturing and decoding of VBI scan lines are typically performed by hardware. While the prior art hardware approach offers the opportunity to tightly integrate the two operations, the approach has at least the following disadvantages:

a) it is inefficient for each hardware vendor to have to develop its own decoding solution; and

b) it is difficult to mix and match different capture and decoding implementations.

Thus, it is desirable if a common decoding solution can be offered for capture hardware of multiple vendors.

A computer system is programmed with a common VBI scan line decoder to support capture hardware of multiple vendors. The common decoder includes a first and a second function for a capture driver associated with a capture hardware to describe to the common decoder, the sample rate and the line pitch employed by the capture hardware respectively.

In one embodiment, the common decoder further includes a third function for the capture driver to confirm the presence of the common decoder, a fourth function for the capture driver to establish a mechanism for the common decoder to instruct the capture driver/hardware to capture certain scan lines in a vertical blank interval, a fifth function for the capture driver to inform the common decoder the channel being captured by the capture driver/hardware, and a sixth function for the capture driver to request the common decoder to decode a field.

The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:

FIG. 1 is a block diagram illustrating an overview of the present invention;

FIG. 2 is a block diagram illustrating one embodiment of the common VBI scan line decoder of the present invention;

FIGS. 3-4 are flow diagrams illustrating one embodiment of the operational steps of a sample capture driver associated with a capture hardware, invoking the services of the common decoder of the present invention;

FIGS. 5-6 are flow diagrams illustrating one embodiment of the operational steps of the common decoder of the present invention;

FIG. 7 is a block diagram illustrating one embodiment of a software environment suitable for practicing the present invention; and

FIG. 8 is a block diagram illustrating one embodiment of a hardware system suitable for programming with the software environment of FIG. 7.

In the following description, various aspects of the present invention will be described. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some or all aspects of the present invention. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well known features are omitted or simplified in order not to obscure the present invention.

Parts of the description will be presented in terms of operations performed by a computer system, using terms such as data, flags, bits, values, characters, strings, numbers and the like, consistent with the manner commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. As well understood by those skilled in the art, these quantities take the form of electrical, magnetic, or optical signals capable of being stored, transferred, combined, and otherwise manipulated through mechanical and electrical components of the computer system; and the term computer system include general purpose as well as special purpose data processing machines, systems, and the like, that are standalone, adjunct or embedded.

Various operations will be described as multiple discrete steps in turn in a manner that is most helpful in understanding the present invention, however, the order of description should not be construed as to imply that these operations are necessarily order dependent, in particular, the order of presentation.

Referring now to FIG. 1, a block diagram illustrating an overview of the present invention. As shown, in accordance with the present invention, capture driver 12 associated with capture hardware (not shown) of a particular vendor for capturing television signals output.sup.1 by an A/D converter (not shown), including closed captions and teletext scan lines broadcast in the vertical blank intervals of the television signals, invokes common VBI scan line decoder 10 of the present invention to decode captured VBI scan lines 14, thereby freeing the capture hardware vendor from having to provide its own decoding solution. As will be described in more details below, capture driver 12 describes at least the oversampling ratio and the line pitch employed by capture driver 12 and its associated capture driver to generate captured VBI scan lines 14. As will be readily apparent to those skilled in the art, based on the descriptions to follow, common VBI scan line decoder 10 is suitable for servicing capture drivers associated with capture hardware from multiple vendors.

Still referring to FIG. 1, for the illustrated embodiment, capture driver 12 further captures image scan lines 18 from television signals output by the A/D converter. The manner in which image scan lines 18 are stored is dependent on the requirements of the video services employed to render television images from captured image scan lines 18. Any one of a number of video services known in the art may be used. Typically, the video service employed is a function of the software environment. Except for the manner capture driver 12 cooperates with common VBI scan line decoder 10, capture driver 12 is intended to represent a broad category of capture drivers known in the art. Accordingly, except for the manner capture driver 12 cooperates with common VBI scan line decoder 10, capture driver 12 will not be otherwise further described.

For the illustrated embodiment, common VBI scan line decoder 10 stores decoded VBI scan lines into VBI stack 16 for a data stream interpret to interpreter the decoded VBI scan lines for an application. Implementation of VBI stack 16 is well within the ability of those skilled in the art, accordingly, it will not be further described either.

FIG. 2 illustrates one embodiment of common VBI scan line decoder 10 (hereinafter simply common decoder). As shown, for the illustrated embodiment common decoder 10 includes first function 20 and second function 22 for capture driver 12 to inform common decoder 10 of the oversampling ratio and the line pitch employed by capture driver 12 and its associated capture hardware to capture VBI scan lines 14.

The oversampling ratio specifies the sampling ratio of capture hardware's A/D frequency to the scan line data bit frequency. For example, if capture hardware's A/D frequency is 28.636 Mhz, and the data bit frequency is in accordance with North American Broadcasting Television Specification (NABTS) for teletext.sup.2, i.e. 5.7272 Mhz, the oversampling ratio is 5. Generally, the oversampling ratio remains constant throughput the course of decoding many fields. However, it may be changed between fields, if there is a need to do so. It is to be appreciated that although the present invention is discussed as informing the common decoder of the oversampling ratio, other conventional methods of indicating the sample rate can also be used within the spirit and scope of the present invention.

For the illustrated embodiment, the oversampling ratios supported are 3.5 to 6.0. The format of the oversampling ratio is a combined integer and remainder values, with the 8 most significant bits of a 32-bit value specifying the oversample integer, and the 24 least significant bits of the 32-bit value specifying the oversample remainder.

The line pitch specifies the spacing in memory between the beginnings of successive captured scan lines, which may be greater than the actual length of a captured scan line. However, for the illustrated embodiment, the spacing is constant, i.e. equally spaced. One or more contiguous captured scan lines form a field. (Note that not all scan lines in a transmitted VBI have to be captured. In other words, some of the transmitted VBI scan lines can be skipped by the capture hardware.)

Continuing to refer to FIG. 2, common decoder 10 further includes third function 24 and fourth function 26 for capture driver 12 to verify the presence of common decoder 10, and to establish a mechanism for common decoder 10 to instruct capture driver 12 to capture certain VBI scan lines. For the illustrated embodiment, third function 24 is a "Get Version" function, and fourth function 26 is a "register callback" function for capture driver 12 to register a callback function for common decoder 10 to call capture driver 12 to instruct capture driver 12 to start capturing certain VBI scan lines. In an alternate embodiment, in lieu of registering a callback function, capture driver 12 uses function 26 to poll common decoder 10 whether it is time for capture driver 12 to capture scan lines. As will be appreciated by those skilled in the art, capturing VBI scan lines only when it is necessary to do so reduces CPU cycle consumption, and improves overall system efficiency.

Still referring to FIG. 2, common decoder 10 further includes fifth function 28 and sixth function 30 for capture driver 12 to inform common decoder 10 which channel is being captured by capture driver 12 and the associated capture hardware, and request common decoder 10 to decode a field. For the illustrated embodiment, when requesting common decoder 10 to decode a field, capture driver 12 informs common decoder 10 where in memory to find the field to be decoded, which scan lines were captured, and whether the field is an odd field or an even field. (Closed Caption data are located in odd fields.) For the illustrated embodiment, the memory location is conveyed in the form of an address pointer; the VBI scan lines captured is conveyed in the form of a bit mask, e.g. 0.times.00208000 standing for lines 15 and 21 (and no others) are captured.sup.3 ; the odd/even information conveyed in the form of a flag.

Before describing common decoder 10 further, we will first describe one embodiment of the operational flow of capture driver 12, referencing FIGS. 3-4. As shown in FIG. 3, for the illustrated embodiment, prior to invoking common decoder 10 to decode a field, capture driver 12 first invokes the "Get Version" function 24 to verify the presence of common decoder 10, step 42. Upon confirming the presence of common decoder 10, capture driver 12 invokes the "register" function 26 to register a callback function with common decoder 10 for common decoder 10 to instruct capture driver 12 to capture VBI scan lines, when it is time to do so, step 44. As discussed earlier, in an alternate embodiment, capture driver 12 may simply poll common decoder 10 from time to time, as opposed to registering a callback function. Next, capture driver 12 invokes the "set" functions 20, 22, and 28 to inform common decoder 10 of the oversampling ratio and the line pitch being employed, as well as the channel being captured, steps 46-50.

As shown in FIG. 4, for the illustrated embodiment, upon completing the above described set up steps, capture driver 12 waits for capture instructions from common decoder 10, step 52. Once received, capture driver 12 through capture hardware captures the VBI scan lines instructed, step 54. Upon capturing the requested VBI scan lines, capture driver 12 invokes the "decode" function 30 to request common decoder 10 to decode the field containing the captured VBI scan lines, step 56. If capture driver 12 has not been told to stop, it repeats steps 54-56 field after field until it has been told to stop. At such time, capture driver 12 returns to step 52.

We now continue to describe common decoder 10, referencing FIGS. 5-6, wherein one embodiment of the operational flow of common decoder 10 is illustrated. As shown in FIG. 5, for the illustrated embodiment, in response to each function invocation, common decoder 10 performs the requested function. For the illustrated embodiment, upon invocation, "Get Version" function 24 returns a major and a minor version number. For "Register" function 26, upon invocation, it returns a line bit mask if scan line data are desired at the time, otherwise a null indicator. For "Set Oversampling Ratio" function 20, upon invocation, function 20 verifies whether the specified ratio is acceptable. For the illustrated embodiment, acceptability simply means compatibility. Function 20 also determines the oversampling ratio for Closed Caption. For example, if the oversampling ratio specified is 5.0, and the scan line's frequency is accordance with NABTS for teletext, function 20 will internally determine the oversampling ratio for Closed Caption to be 56.87 (5.0.times.11.37, since NABTS teletext data rate is 11.37 times the Closed Caption data rate of 0.5035 Mhz). If the ratio is acceptable, an "OK" status is returned, otherwise, an error status is returned. Similarly, for "Set Line Pitch" function 22, upon invocation, function 22 verifies whether the specified line pitch is acceptable. For the illustrated embodiment, acceptability means the line pitch set is greater than the actual line size of a captured scan line. If the line pitch is acceptable, an "OK" status is returned, otherwise, an error status is returned.

For "Set Channel" function 28, upon invocation, function 28 resets various internal operational parameters, for the illustrated embodiment, including anti-ghosting support as well as performance and signal quality monitoring statistics. Anti-ghosting support may include the improved techniques disclosed in co-pending U.S. Patent Applications, serial numbers, <insert two serial numbers>, entitled A Mechanism for Adaptive Selection of Anti-Ghosting Filtering, and A Self-Correcting Anti-Ghosting Process, invented by the inventor of the present application, and filed contemporaneously with the present application. If all resetting operations are successfully performed, "Set Channel" function 28 returns an "OK" status, otherwise an error status. For "Decode Field" function 30, upon invocation, function 30 decodes the requested field, and stores the decoded data in VBI stack 16 as described earlier. For the illustrated embodiment, function 30 includes the channel identification in all stored data. If the decode operation is performed successfully, an "OK" status is returned, otherwise an error value is returned. In either case, a bit mask denoting scan lines to be captured in the next field may also be returned. Decoding operation may include the improved run-in clock recovery technique disclosed in copending US Patent Application, S/N<insert serial number>, entitled Noise Tolerant Run-In Clock Recovery Method and Apparatus, invented by the inventor of the present application, and filed contemporaneously with the present application.

As shown in FIG. 6, in addition to the above described processing performed in response to the invocation of functions 20-30, during operation, common decoder 10 monitors for capture events, step 64. In response to the detection of a capture event, common decoder 10 calls capture driver 12 and instructs capture driver 12 to capture the appropriate VBI scan lines, step 66. Capture events include status changes by a client application, e.g. the client application asking for a new type of data, or common decoder 10 concluding on its own that certain scan lines no longer contain useful data.

Referring now to FIG. 7, wherein a block diagram illustrating one embodiment of a software environment suitable for practicing the present invention is shown. As shown, for the illustrated embodiment, VBI decoder 10, capture driver 12, image scan lines 14, VBI scan lines 16, and VBI stack 16 cooperate with each other as described earlier. Additionally, image scan lines 14 are processed by device dependent video drivers 106, e.g. VfW drivers that implement Microsoft DirectX.TM. video support, which in turn provides the processed data to a device independent video service 104, e.g. Microsoft Video for Windows. The device independent video service 104 then generates the television images for application 102. With respect to the decoded scan lines, e.g. teletext or closed captions), data stream interpreter 108 interprets the decoded VBI scan lines for application 102.

FIG. 8 illustrates one embodiment of a hardware system suitable for programming with the software elements of FIG. 7. As shown, for the illustrated embodiment, hardware system 200 includes CPU 202 and cache memory 204 coupled to each other as illustrated. Additionally, hardware system 200 includes high performance I/O bus 206 and standard I/O bus 208. Host bridge 210 couples CPU 202 to high performance I/O bus 206, whereas I/O bus bridge 212 couples the two buses 206-208 to each other. Coupled to bus 206 are system memory 214 and video memory 216. In turn, display device 218 is coupled to video memory 216. Coupled to bus 208 is mass storage 220 and keyboard and pointing device 222.

These elements 202-222 perform their conventional functions known in the art. In particular, mass storage 220 is used to provide permanent storage for the programming instructions implementing the above described functions, whereas system memory 214 is used to provide temporary storage for the programming instructions when executed by CPU 202. Mass storage 220 may be provided with the programming instructions by loading the programming instructions from a distribution storage medium (not shown), or by downloading the programming distributions from a server (not shown) coupled to hardware system 200 via a network/communication interface (not shown). Collectively, these elements are intended to represent a broad category of hardware systems, including but not limited to general purpose computer systems based on the Pentium.TM. processor, manufactured by Intel Corp. of Santa Clara, Calif., assignee of the present invention.

Thus, a method and apparatus for common VBI scan line decoding has been described. While the method and apparatus of the present invention has been described in terms of the above illustrated embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described. The present invention can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of restrictive on the present invention.