Teletext VBI

This module contains an element capable of sending EBU teletext data from a transport stream to the TV using the VBI resource provided by the Hardware Abstraction Layer (HAL) through the Hardware Abstraction Interface (HAI).

Loadable Module Properties

Module Name Teletext VBI element
File Name libteletextvbi.so
Class Count1

Element Quick Index

DVB Teletext VBI Inserter.

DVB Teletext VBI Inserterr in typical pipeline.

Teletext VBI Element

The teletext VBI element fetches the teletext data from the PES stream. The element depends on the teletext page information being previously decoded from the teletext_descriptor of a DVB encoded stream (ETSI EN 300 468).

Class Properties

Name Teletext VBI Descriptor
Version1
Interface Name IElementDescriptor
BindingC++

Element Descriptor

Name DVB Teletext VBI Inserter
TypeIntermediary
Priority500
Input Formats MPEG-2/Transport Stream/Multi Subtitle
Output Formats MPEG-2/Transport Stream/Multi Subtitle

Metadata

Key Input Output
_ActiveTeletextStreamProducedCommitted
_TeletextStreamList RequiredCommitted

Theory of Operation

On ISink::Activate(), it opens the HAI VBI resource instance 0 (zero) in exclusive mode. The HAI resource is closed on ISink::Deactivate().

The element filters the stream based on the value of the _RequestTeletextStream blackboard parameter, which holds the id of the teletext stream selected by the user. If this parameter does not exist, the element chooses the first stream in the _TeletextStreamList as default. The _TeletextStreamList parameter is described in greater detail in the Complex Metadata section.

The element decodes all PES packets having the stream_id field set to private_stream_1 (0xbd). When a complete VBI field is fetched it is sent to the VBI resource.