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IAMLine21Decoder interface

The IAMLine21Decoder interface sets and retrieves information about closed captions.

The Line 21 Decoder filter exposes this interface. Applications can use this interface to enable or disable closed captions, select the closed captioning service, and set other closed captioning properties.

Closed-captioned information is transmitted on line 21 of field 1 in the vertical blanking interval (VBI) of television signals. Video cassette recorders record this information on video tape, and you can use the Line21 Decoder and other DirectShow filters to capture the line 21 data and save it on disk in a media file format such as Audio-Video Interleaved (AVI). The closed-captioned information appears as a separate stream within the media file.

Closed-captioned text is used in television programming and DVD movies. DVD movies contain line 21 data as part of the user data section of each Group of Pictures (GOP) in the video stream. Television receiver cards with Windows Driver Model (WDM) drivers provide line 21 data.

Members

The IAMLine21Decoder interface inherits from the IUnknown interface. IAMLine21Decoder also has these types of members:

Methods

The IAMLine21Decoder interface has these methods.

MethodDescription
GetBackgroundColor

Retrieves the background color used by the Line 21 Decoder filter for overlay.

GetCurrentService

Retrieves the current closed captioning service.

GetDecoderLevel

Retrieves the closed-captioned decoder level.

GetDrawBackgroundMode

Indicates whether the filter draws the captions on a transparent background or an opaque background.

GetOutputFormat

Retrieves the Line 21 Decoder filter's output format.

GetRedrawAlways

Indicates whether the filter redraws the entire output bitmap for each sample.

GetServiceState

Indicates whether closed captioning is on or off.

SetBackgroundColor

Sets the background color that the filter uses for overlay.

SetCurrentService

Sets the closed captioning service.

SetDrawBackgroundMode

Specifies whether the filter draws the captions on a transparent background or an opaque background.

SetOutputFormat

Sets the filter's output format. (Not implemented)

SetRedrawAlways

Specifies whether the filter redraws the entire output bitmap for each sample.

SetServiceState

Enables or disables closed captions.

 

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Il21dec.h

Library

Strmiids.lib

 

 

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