In Broadcast - February 2018 - 27
www.inbroadcast.com | Vol: 8 - Issue 2 | February 2018
Cavena Subtitle Solution
For OTT Platforms
(technically the same thing)
transmission in OTT platforms for
linear channels is usually handled by
taking subtitles from the video feed
for the channel and converting it to
the various OTT transmission formats
The video signal, typically SDI or DVB
TS, contains EBU teletext (SDI) or DVB
Teletext, ETSI 300 743 (TS) subtitles.
These can be converted to the OTT
formats as they are text based.
In some cases there is no subtitle
data available, except in the format of
subtitles as visible on the TV screen,
referred to as DVB bitmaps. This can
be solved by Cavena OCR reading the
subtitles for conversion to text.
Note that, if a Cavena transmission
system is installed on site, the subtitle
data is already available, it's just
another port on the Cavena STU,
interfacing the OTT platform.
Because teletext is limited to European
languages, it cannot handle Asian
languages. Cavena has developed a
proprietary format used in packet
31 generic data transmission in EBU
teletext to carry Asian languages
as well as features not available
in teletext such as more exact
positioning, more than 37 characters
per row, frame accurate pretransmission etc. The Cavena subtitle
format is transmitted in the P31
generic data transmission of teletext
and thus works with any signals and
systems handing teletext, including
SD-SDI, HD-SDI (OP-47/SMPTE-2031)
and DVB Teletext.
Use of this format in an OTT platform
means it can now handle Asian
languages and any other language in
the world not supported by teletext.
Support for this format is added
to the OTT platform to be able to
interpret the data and convert it to the
transmission formats like WebVTT etc.
If the incoming video is a DVB TS
containing DVB bitmap subtitles (ETSI
300 743), it is harder to convert to OTT
formats as the bitmaps have to be OCR
read. Cavena provides solutions to OCR
and transcode DVB bitmap subtitles
to all available transmission formats,
including EBU Teletext, DVB teletext
and the Cavena P31 format.
OCR reading is not 100% correct at
all times and requires "training" to
work well with each individual font
coming in. OCR reading works for any
language, any font. Note that nonLatin characters can only be supplied
to the OTT platform with Cavena P31.
Cavena's OTT subtitle solution