Teletext subtitles are defined in the specification ETSI EN 300 706. A corresponding specification for subtitles files in STL file format with support for teletext subtitles is defined in TECH. 3264-E.
Teletext subtitles are always transported in the invisible part of the video signal and are therefore not visible in the picture. The receiver (TV set or DVB receiver) must decode teletext subtitles and overlay these subtitles over the video on the receiving device.
- In SDI Video (Serial Digital Interface) this is generally in ANC part of the signal as OP47 or SMPTE2031.
- In TS (Transport Stream) this is in a separate PID (Program ID) which is signaled in the PMT (Program Map Table) so that the receiver knows which PID with teletext subtitles corresponds to which video PID.
To decode teletext subtitles from SDI video and display them some solutions would be:
- Tektronix WVR8300 with teletext option can analyze SDI video and also display teletext subtitles
- FAB Subtitler PRO software with FAB FT-HT 14 SDI card can decode teletext subtitles from SDI video and display them on PC screen
To decode teletext subtitles from TS and display them some solutions would be:
- FAB Subtitler PRO software can receive a TS/IP unicast/multicast stream, decode teletext subtitles and display them on PC screen.
- For DVB-S/S2/T/C a DVB Receiver like GigaBlue UHD Quad 4K Pro Linux E2 with alternative software from www.openpli.org is a very good solution to decode teletext subtitles and display them over the picture.
FAB solutions for teletext subtitles
The following FAB solutions can be used for teletext subtitles:
- Transmission of teletext subtitles in SDI
- Transmission of teletext subtitles over TS/IP or TS/ASI
- Insertion into TS files
- Insertion into MXF files
1. Transmission of teletext subtitles in SDI
FAB Subtitler BCAST/XCD can transmit subtitles over network to FAB Teletext Subtitle Generator which generates a teletext stream with one or more teletext subtitle pages. The teletext stream can be inserted into one or more different SDI signals by FAB SDI PCIe card.
2. Transmission of teletext subtitles over TS/IP or TS/ASI
FAB Subtitler BCAST/XCD can transmit subtitles over network to FAB Teletext Subtitle Generator which generates a teletext stream with one or more teletext subtitle pages. The teletext stream can be transmitted as TS/IP or TS/ASI synchronized to a PCR by FAB DVB Interface.
3. Insertion into TS files
FAB Subtitler PRO/LIVE/MPEG can open subtitle files in many different formats and insert the subtitles from the subtitle file as DVB bitmaps into a TS file as a stream with a separate PID. Watchfolder operation is supported but FAB Subtitler MPEG is required to be able to control FAB Subtitler using a REST interface.
4. Insertion into MXF files
FAB Subtitler MPEG can open subtitle files in many different formats and insert teletext subtitles from the subtitle file as teletext subtitles into MXF files into VBI/VANC. Watchfolder operation and control of FAB Subtitler using a REST interface are available.