DVB Subtitles

DVB subtitles are defined in the specification ETSI 300 743. DVB subtitles are transmitted in a TS (transport stream) in a separate PID (ProgramID) and not within the video PID. It is possible to transmit multiple PIDs with DVB subtitles, for example a different language within every PID.

The receiving device generally has a selection menu to select the language of the subtitles. It then starts receiving the DVB subtitle PID with the selected language, extracts subtitle bitmaps and displays subtitle bitmaps overlaid over the video.

It is very important that timestamps of the DVB subtitling PID correspond correctly to the timestamps of the PCR PID or video PID because this is how the receiver knows the exact time when a subtitle bitmap has to be displayed. This synchronization of the DVB subtitle PTS (presentation time stamps) to the PCR PID / video PID is a key feature of the FAB DVB subtitling system.

The DVB subtitling specification allows transmitting subtitles as bitmaps but also as text characters. However because the transmission of subtitles as text characters is not well defined most DVB receivers can only receive and display bitmap based DVB subtitles.

You will find a short explanation of DVB transmission concepts here.

FAB solutions for DVB subtitles

The following FAB solutions are available for DVB subtitles:

  • Transmission as TS/IP or TS/ASI with FAB DVB Interface
  • Insertion into TS files

1. Transmission as TS/IP or TS/ASI with FAB DVB Interface

DVB subtitles are transmitted in a separate PID by FAB DVB Interface. FAB Subtitler BCAST/XCD sends bitmap subtitles over network to FAB DVB Interface. Bitmap subtitles are converted to a DVB subtitle stream and transmitted in a separate PID. The PTS of the transmitted PID is synchronized to the PCR which is received from the DVB multiplexer.

2. 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.