In DVB (and IPTV systems that use MPEG TS) Teletext is sent in its own pid, along with the audio and video pids of the program being watched ( for the details you can check ETSI 300 472).

vlc btw contains a decoder for teletext pages, you can tune in to a dvb stream and look at them.

Trivia: in some countries (for instance in Switzerland) subtitles for movies are sent sometimes as semitransparent teletext pages (in CH it is on page 777) even if DVB supports natively subtitles.