The logical solution for Broadcasters is to add the subtitles during playout and for a single channel it will look as described.
The subtitles are produced by subtitle translators operating a subtitle preparation stations, Tempo is the Cavena solution. Tempo plays back browse quality video frame accurately and the subtitle translator produces subtitle files with text and time code. The subtitle files are stored in the Cavena Subtitle Archive Management system, SAM, after having been tested for technical errors.
File based playout of subtitles
Cavena Subtitle Transmission Controller, STC, receives a playlist from the Traffic system or from the Station Automation. STC uses the playlist as the order to copy files from SAM to the buffer directory on STC. STC is interfaced to the Station automation and when a new program is started STC receives Prepare and Start commands for the channel and item that is to be transmitted.
The STC in turn controls Cavena Subtitle Transmission Unit, STU. STU uses a time code reader and will play the subtitle files associated with a specific program. Each language has a separate subtitle file with text and time code. STU is capable of playing out the subtitles in one or several formats. Thus one program can have both DVB Bitmap and Teletext associated with it. It is even possible to feed different outputs of the program with different format subtitles. For instance analogue teletext to A output DVB Bitmap to B output and HD in-vision to C output, all to the same program. All subtitles being frame accurate in respective output since STU can have different delays for different ports.