In Broadcast - July 2012 - 65
ISSUE 10 - JULY 2012 | WWW.INBROADCAST.COM
InFORM Subtitling Explained
By Henrik Moberg, Managing Director, Cavena Image Products
When it comes to television access, subtitling is very important. It is utilised for two main reasons - to make foreign language material accessible, and to aid hearingimpaired people. Translation subtitling allows a broadcaster to reach multiple language target audiences, which makes it ideal for targeting multiple language groups. The viewer can select the language to receive. For hearing-impaired people, subtitling allows them to follow television, and is a legal requirement in many countries. The advantage of subtitling over dubbing is cost. Subtitling is much cheaper per language to produce than alternative language audio tracks. Also, a new subtitling language can easily be added whenever needed, even after material preparation is done. Subtitling is not an exact translation, because differences between languages often require additional information to understand the original content. Subtitling often compresses the language to ﬁt the dialogue into as little text as possible, to avoid distracting the viewer.
Subtitling comprises two stages preparation and transmission. The preparation of the subtitle files, along with the timecode required to synchronise the subtitle with the video, is done ahead of transmission. These are delivered to the transmission site in a format deﬁned by the broadcaster, and stored until needed for transmission. Subtitle transmission is an automated process. The equipment interfaces to station planning and automation systems to receive programme and trigger information. The transmission units then synchronise the subtitles for playout using the video timecode. Subtitles are output in suitable formats for the transmission platform. There are two types of subtitling - open and closed. Open subtitling is visible to all viewers, typically for translations of foreign language material. This is useful for national broadcasters that broadcast foreign material. Open subtitling uses a dedicated inserter for overlaying subtitles in the video signal, so the
subtitling is always visible. Closed subtitling is transmitted as separate data in the transmission, so is ideal for multilingual subtitling and subtitling for the hearing impaired. DVB subtitling and EBU teletext transmission formats are common, which is decoded and inserted into the picture at head ends or set-top boxes. DVB subtitling is bitmap based, so font and appearance is deﬁned by the broadcaster. EBU teletext is character based, and therefore relies on the decoder’s character generator for appearance, so is limited to teletext character sets. Transcoding can be reading subtitles in VBI format and instantaneously converting and re-sending subtitles in DVB format, with no dependence on timecode. Cavena has this solution integrated as part of its transmission products and can switch between timecoded subtitle ﬁle playout, and transcoding from one subtitling format into another. Live subtitling is also supported. The required equipment depends on what is, or is to be, installed, and the technology used for distribution of TV and subtitles. At the playout centre, the key subtitle components are: • Storage, QC check and archiving with Cavena SAM; • Transmission control and automation interface with Cavena STC; • Playout of subtitles with Cavena STU; • SDI subtitle insertion with Cavena Cimpress. Cavena specialises in subtitling, and has assisted many customers in the design and conﬁguration of cost effective subtitling solutions, including back up installations. Timecode or transcode? Cavena can assist with the answers. ■
Cavena at work