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AVStream Driver Reference Information
82 ViewCast
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 58. Captioning via CC or VBI pins
The driver supports the standard DirectShow CC and VBI pins (on the Osprey 530/540/560, the CC
pin only; on the other products, both pin types). 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 4.0.0 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 on rendered onto preview video. The Line 21
Decoder downstream of the Osprey 530/540/560 capture filter interprets the CC pairs and renders
an overlay of the characters. 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.