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As some of
you might know, most digital European television broadcasts use the Digital
Video Broadcast standard (DVB), this includes cable TV (DVB-C), satellite TV
(DVB-S) and terrestrial TV (DVB-T).
In the good
old days of analog broadcasts, subtitles (in those countries where they are
used) where transmitted as part of the video image (and hence there was of
course no way to turn them off, or allow multiple languages). Such subtitles
are called ‘embedded’ or ‘burned-in’ subtitles.
DVB offers
3 additional ways to provide subtitles to the viewer:
The first
is bitmap subtitles. In this case a separate image is transmitted for each
subtitle language, allowing the viewer to select which (if any) subtitles to
overlay on the video image.
The second
is teletext subtitles (these are also sometimes available on analogue
broadcasts). In this case some teletext pages are marked as containing
subtitles, containing the subtitle text to be rendered.
The third
is code-based subtitles, which are text subtitles similar to the teletext
subtitles, but without the dependence on the old teletext standard.
Bitmap
subtitles are not supported by all old set-top boxes, and therefore it is
mostly used on broadcasts where people are buying new boxes anyway (High
definition channels and DVB-T).
For most
other channels either teletext subtitles or embedded subtitles are used. We are
not aware of code-based subtitles being in use.
MediaPortal
currently has some limited support for teletext subtitles by way of using the
Teletext module found in MyTV and no support for bitmap subtitles (embedded
subtitles are of course supported as they don’t actually need any support :)
However, thanks to tourettes we are now on our
way to having a DVB subtitle DirectShow filter, which when it is finished will
support both bitmap subtitles and teletext subtitles. We aim to create it in such a way
that the user won’t have to worry about the difference between the two types of
subtitles, and it will additionally automatically select the correct subtitle
stream based on language preference. Subtitles will be available for both live
and recorded TV. The recording format must be Transport Stream in order to
preserve subtitles in recordings and timeshift buffer. As you might have
guessed the filter is therefore only available with TVE3.
You can
track the current status of the work-in-progress as well as find information on
how to help test the filter in this thread :
The
developers involved on this are tourettes who have been doing most of the work,
and me (Ziphnor) working on the teletext part (and a bit on the rendering
part).
Users' Comments (12) 
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