This section defines requirements for television tuner capabilities and VBI data capture capabilities in support of the Windows Broadcast Architecture. This architecture is designed to enable a wide rage of data broadcasting services, including the use of decoded data captured from broadcast television signals during the vertical blanking interval (VBI) as well as from video scan lines. An Entertainment PC 98 system must include both television tuner and VBI capture capabilities.
For more information about the operating system Broadcast Architecture and capabilities supported by Windows operating systems, see the Windows NT 5.0 DDK and the white papers available from http://www.microsoft.com/windows/tv/.
Cable and broadcast television data networks can inject digital data into any or all video scan lines, including those usually used for images, in the same way that VBI lines can contain data. In general, a VBI decoder refers to the processing of the raw VBI samples into data packets. VBI capture refers to an analog-to-digital converter (ADC) taking VBI samples of VBI data bits. A VBI decoder takes those samples and performs additional processing to determine bit values from the samples. The VBI decoder also handles specific encoding schemes.
VBI decoding can be performed either in hardware or in software. Software VBI decoders need access to oversampled VBI data. In operation, a VBI decoder is similar to a network adapter, except that the data flow is receive-only.
Notice that some requirements in this section specify support related to NABTS data or other locale-specific formats. Devices designed for locales that support other standards do not have to meet these requirements. However, some requirements specify NABTS as an example data format; in these cases, the device must meet the requirements for relevant locale standards.
Important: A PCI-based tuner and VBI capture or decoder device must meet the PC 98 requirements for bus mastering. A video port is also highly recommended for all implementations, as defined in the “System Requirements for Video and Broadcast Components” section earlier in this chapter.
24. Television tuner supports PC 98 audio and video performance
Required
The audio and video performance capabilities for a television tuner are similar to those defined in the “MPEG-2 Playback Requirements” section earlier in this chapter, including the following:
25. Television tuner includes stereo tuner and supports SAP
| Consumer PC 98 | Office PC 98 | Entertainment PC 98 |
| Recommended | Recommended | Required |
This requirement includes support for a secondary audio programming (SAP) channel.
For devices designed for use in Europe and South Africa, the device should support Near-Instantaneously Companded Audio Multiplex (NICAM 728) as the standard for digital multichannel sound transmission.
26. VBI capture oversamples VBI data at least four times
Required
To ensure accurate data reception, data transmitted on all lines of the VBI must be oversampled at least four times the NABTS data bit rate (or locale-specific data bit rate). For example, if there are 288 bits of NABTS data on a scan line, approximately 1,152 bits plus the necessary margin (that is, the number required for timing tolerances in the NABTS specification and also for timing uncertainties within the capture hardware) must be captured per scan line.
27. VBI capture detects validity of scan-line data
Required
Each scan line designated for data reception provides a confidence indication about the quality of the received signal (0–100). This is based on the errors encountered in performing the A-to-D. This confidence information will be used to adjust the ranges of decoded scan lines. This QOS will be used to discover the data available on each possible scan line.
28. VBI capture makes VBI data available to the CPU for processing
Required
Raw data samples from VBI lines must go into host memory that can be addressed by the CPU. This data is used to read data encoded into broadcast transmissions, such as closed captioning, NABTS, and Teletext.
To minimize the CPU bandwidth required to process VBI data, the hardware must have the ability to bus master all individual scan lines to different host buffers.