- TELETEXT & SUBTITLING SYSTEMS
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Subtitling - Subtitling Types
The FAB Subtitling System supports the following types of subtiting:
Open subtitles are inserted into the visible part of the TV picture already at the TV station before the TV signal is transmitted. This procedure enables the viewers to see subtitles without the need for using a special decoder in the TV set. However this way only one language can be transmitted at a time. By trying to transmit more languages a very large part of the TV picture would be covered by the subtitles or one line per language must be used which limits the number of languages.
FAB Subtitler can insert open subtitles into SDI video and into MXF video files.
Teletext subtitles are used to transmit subtitles as teletext data in the invisible part (VBI/VANC) of the TV picture. This kind of subtitling is mainly used in Europe. Teletext data is decoded by the teletext decoder in the TV set and displayed on the TV screen. This way it is possible for each viewer to decide whether he wants to see subtitles or not. In case that he wants to read the subtitles he simply selects the subtitle page number (usually 777 or 888) on the teletext decoder and the subtitles will be displayed over the TV picture. By selecting between different teletext page numbers it is possible to define the subtitle language which should be displayed on the screen. The big advantage of teletext subtitles is that standards exist that define how to store and transfer teletext subtitles within SD-SDI, HD-SDI, Transport Stream, MXF, TCP/IP and EBU STL files.
DVB subtitles are similar to teletext subtitles. DVB subtitles are transmitted as bitmap data (not overlaid over the video) in the DVB signal in a separate PID and the DVB set top box decoder decodes subtitles and displays them over the video. Multiple languages can be transmitted by using separate streams for every subtitle language.
Closed captions CEA-608 and CEA-708 are american standards used for transmission of subtitles for hearing impaired person with the invisible part (VBI/VANC) of SDI video. CEA-608 was used for analogue transmissions and CEA-708 is used for digital transmissions and for tunneling of CEA-608 data in digital signals.
Internet streaming subtitles are covered by different standards. Mostly the file format DFXP XML is used combined with protocols like HLS and MPEG-DASH to transfer DFXP XML files for subtitling of internet TV streaming.
DVD & Blu-ray subtitles are similar to teletext subtitles which means that they are not inserted into the visible part of the TV picture but onto a separate track of the DVD/Blu-ray disk. The DVD/Blu-ray player will read the subtitles from the separate track and overlay the subtitles over the picture. Because there are many subtitle tracks available on one DVD/Blu-ray it is possible to record subtitles in multiple languages onto a single DVD/Blu-ray disk.
Digital Cinema subtitles are generally based on XML files containing text and timecode for the subtitles. Optionally high quality image files may also be provided to the digital cinema projector.