Tvheadend

It's a bit optimization request. The teletext subtitles mark end with the empty text.

Thinking more about this - it's not an easy one. The teletext really ends the subtitles with the zero text, so we don't know the duration when the subtitle is started and if we wait to the end mark (empty text), the subtitle will be muxed to the matroska too late (after video/audio). We can do this with more queuing at the muxer side, but it will cost more latency.