WST Codec Filter

World Standard Teletext (WST) is the European standard for data transmission using VBI on PAL analog television signals. Both captioning and data services are provided using this standard. The WST Codec is a kernel-mode filter that receives raw VBI samples and, optionally, decoded Teletext samples from the Capture Filter via the Tee/Sink-to-Sink Converter filter. This codec decodes and/or duplicates the decoded and forward-error-corrected Teletext data for the WST Decoder filter. The WST Codec corresponds to the CC Decoder filter for NTSC transmissions. The WST Decoder corresponds to the Line 21 Decoder for NTSC; these filters create the bitmaps that are sent to the Overlay Mixer (or the Video Mixing Renderer on Windows XP Home Edition and Windows XP Professional).

This filter has two input pins, VBI and HWCC. The VBI pin is used for raw VBI data, and the HWCC pin is used when the VBI decoding is performed in hardware by the capture filter. When the data is received on the HWCC pin, the WST Codec operates in "pass-through" mode, and sends the data directly to the WST Decoder without processing it in any way. If the capture filter exposes an HWCC pin, it must be connected directly to the corresponding pin on the WST Codec (pin category .

The WST Codec appears in GraphEdit in the "WDM Streaming VBI Codecs" category. Because this is a kernel-mode filter, applications cannot co-create it directly, but must use the System Device Enumerator to instantiate it, as described in Enumerating Devices and Filters.