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Osprey 240e/450e User Guide
ViewCast 77
Closed captioning (CC)
The Osprey AVStream driver supports NTSC closed captions in three separate ways.
Through standard DirectShow CC and VBI pin
By rendering captions directly onto video on the capture or preview pin; the captioned
video can be streamed, written to file, or rendered directly
Through an Osprey custom property
On products other than the Osprey 530/540/560, the driver also provides PAL/SECAM captions as well
as teletext data in raw form via the VBI pin (not through the CC pin). Refer to the next section on Vertical
Blanking Interval (VBI) Capture for more information. The rest of this section is specific for NTSC
captioning only.
Captioning via CC or VBI pins
Figure 67. CC or VBI pins
The driver supports the standard DirectShow CC and VBI pins. The CC character pair data can be
streamed to applications such as Windows Media Encoder 9, or rendered directly to the screen using
the DShow Overlay Mixer filter. The 4.6 driver can be set to output CC field 2 character pairs on the CC
pin, instead of the standard CC field 1 data. XDS (Vchip) data is embedded in the field 2 stream.
The GraphEdit filtergraph shown here displays CC rendered onto preview video. The Overlay Mixer
combines the CC overlay with the preview video, which is then rendered onscreen. It is also possible to
capture the character pair stream as a standard stream of an AVI file, (although there will be problems
with timestamping and synchronization); or, to directly manipulate the CC stream in a standard way
with a custom application.
Our testing with the current version of DirectX 9 indicates that closed captions do not render properly
with the VMR9 renderer in place of the Overlay Mixer / Video Renderer combination. Therefore, the
default Video Renderer in combination with Overlay Mixer should be used.
When SimulStream is not installed, the driver supports two CC pin instances. One could be associated
with the video capture stream, the other with the preview stream. In practice, a DirectShow Smart Tee
Filter can be inserted into the graph to make any number of VBI pins. When SimulStream is installed,
you can have two CC pin instances per SimulStream filter.
The driver has three built-in user-accessible controls that affect Closed Captioning.