IAMLine21Decoder interface (il21dec.h)
[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]
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.
Inheritance
The IAMLine21Decoder interface inherits from the IUnknown interface. IAMLine21Decoder also has these types of members:
Methods
The IAMLine21Decoder interface has these methods.
| IAMLine21Decoder::GetBackgroundColor The GetBackgroundColor method retrieves the background color used by the Line 21 Decoder filter for overlay. The default background color is magenta. |
| IAMLine21Decoder::GetCurrentService The GetCurrentService method retrieves the current closed captioning service. |
| IAMLine21Decoder::GetDecoderLevel The GetDecoderLevel method retrieves the closed-captioned decoder level. |
| IAMLine21Decoder::GetDrawBackgroundMode The GetDrawBackgroundMode method indicates whether the Line 21 Decoder filter draws the captions on a transparent background or an opaque background. By default, the caption background is opaque. |
| IAMLine21Decoder::GetOutputFormat The GetOutputFormat method retrieves the Line 21 Decoder filter's output format. |
| IAMLine21Decoder::GetRedrawAlways The GetRedrawAlways method indicates whether the Line 21 Decoder filter redraws the entire output bitmap for each sample. |
| IAMLine21Decoder::GetServiceState The GetServiceState method indicates whether closed captioning is on or off. |
| IAMLine21Decoder::SetBackgroundColor The SetBackgroundColor method sets the background color that the Line 21 Decoder filter uses for overlay. The default background color is magenta. |
| IAMLine21Decoder::SetCurrentService The SetCurrentService method sets the closed captioning service. |
| IAMLine21Decoder::SetDrawBackgroundMode The SetDrawBackgroundMode method specifies whether the Line 21 Decoder filter draws the captions on a transparent background or an opaque background. By default, the caption background is opaque. |
| IAMLine21Decoder::SetOutputFormat The SetOutputFormat method sets the Line 21 Decoder filter's output format. |
| IAMLine21Decoder::SetRedrawAlways The SetRedrawAlways method specifies whether the Line 21 Decoder filter redraws the entire output bitmap for each sample. |
| IAMLine21Decoder::SetServiceState The SetServiceState method enables or disables closed captions. |
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows 2000 Professional [desktop apps only] |
| Minimum supported server | Windows 2000 Server [desktop apps only] |
| Target Platform | Windows |
| Header | il21dec.h |