Subtitle Transmission – Introduction

 

The Cavena subtitling system is modular built of special software modules and dedicated hardware modules. With special hardware for time code reading, insertion and reading of VBI information such as Line 21 or teletext and graphics generation for SD and HD we accomplish state of the art signal transmission. With modular software design, we combine proven technology solutions with the latest formats and handle interfacing to the latest designs within broadcast technology.

 

Introduction to subtitle transmission

 

Subtitle transmission step-by-step:

The subtitle file complete with text and time code is stored in the Subtitle Archive Management, SAM. Prior to importing, SAM will perform a technical test of the subtitle file.

 

A playlist is sent to STC. This is either sent as text files via a directory to STC (Subtitle Transmission Controller) or automation sends the events via the STC automation interface.

 

The STC will use the playlist as the request list for subtitle files and copy all required subtitle files to the buffer directory and onto the STU (Subtitle Transmission Unit). The STC will receive start commands from the automation system and the STC will command the STU to play out the subtitle files using the time code of program as the reference. Should one STU fail then the STC will control the hand-over to the redundant unit including the switch of proper time code to the redundant STU.

 

One STU per channel builds the complete subtitle for each output format, in-vision SD or HD, teletext, DVB etc. The STU builds, for DVB, the complete transport stream and sends this to the Subtitle Multiplexer, S-MUX.

 

The S-MUX multiplexes the subtitles for many channels and sends this onto the video multiplexer via IP or ASI The S-MUX also reads and decodes the Program Clock Reference, PCR, for every channel which is subsequently sent to the correct STU.

 

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