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AVStream Driver Reference Information
80 ViewCast
This capability requires custom programming. Refer to the Osprey AVStream SDK Users’ Guide. A sample
SDK applet named TCApp illustrates the interface.
Figure 69. Timecode Video Marking
Timecode stamping must be enabled in the driver before it can be used, and the field and line number
correctly set. To access the controls, go to the Device property tab and click Extras.
It is recommended that you disable timecode marking when not in use, especially the auto search
feature (on a slow machine it uses several percent of CPU bandwidth) especially if timecodes are not
present.
Note: VITC and LTC – Longitudinal Timecode – are two distinct encoding systems, and this driver
supports only VITC.
A suggested reference on timecode is Timecode: a user’s guide – 3rd ed., John Ratcliff, Focal Press, 1999.
Vertical Blanking Interval (VBI) capture
The Osprey AVStream driver provides DirectShow-compatible VBI pins. VBI data includes Vertical
Interval Timecode (VITC) in both the NTSC and PAL worlds. In NTSC, line 21 Closed Captioning (although
it is part of the video interval rather than true VBI data), is commonly treated as VBI data. In PAL, World
Standard Teletext (WST) is encoded in the VBI data region.
The driver delivers VBI data as raw waveforms, which are then decoded by external DirectShow filters.
DirectShow provides three filters under the classification “WDM Streaming VBI Codecs” that will decode
data from VBI pins:
CC Decoder
NABTS/FEC VBI Codec
WST Codec
With the Osprey AVStream driver, you can use either the CC pin or the VBI pin to obtain closed caption
data. If you use the VBI pin, an extra filter is required to turn the raw waveform into CC character pairs.
When SimulStream is not installed, the driver supports two VBI pin instances. In practice, a DirectShow
Smart Tee Filter can be inserted into the graph to make any number of VBI pins. When SimulStream is
installed, multiple VBI pins are allowed.