[mythtv] [mythtv-commits] Ticket #2468: Mythtranscode removing audio and subtitles and audio tracks swapping places.

[Geoffrey Hausheer]

On 10/17/06, Michael T. Dean wrote:
> > > It is expected that you'll loose your subtitles.  There is no way to
> > convert subtitles from a TS to a PS stream (without a huge amount of
> > work).
> >
> > Please elaborate. I think this is a needed feature ... Should the lack of subtitles be a separate ticket.
> >
> >
> http://mythtv.org/wiki/index.php/Feature_Wishlist
>
I will close all tickets out of hand as won't fix, so no it probably
shouldn't be a ticket.
As far as what is needed....
DVB uses one of:
ETSI EM 300 472 teletext (commonly DVB-TXT) which defines text in
terms of text on a given line number (5 allowed).  This should be easy
to convert into raw text
DVB-VBI (sorry don't have full specs on this, but it is basically what
is used in analog broadcasts, and also text based)  probably not used
much if at all.
ETSI EM 300 743 (commonly DVB-SUB) which can be transmitted as both
text and images, in multiple color depths, and postioned arbitrarily
on the screen.  The streams are tempral based and independant of
audio/video.

DVD Subtitles are bitmap images sent through a seperate stream.  The
images are conditionally overlayed on the original image.  The images
can only have 4 colors (one of which must be the transparent one)

ATSC uses EIA-708 which is text-based, with downloadable fonts.  the
data is stored in the picture rather than in a seperate stream.

So it is a mess.  Converting to DVD standard would be possible for all
of these formats, but requires creating new bitmap images, and quality
would be hit-and-miss.  DVB-SUB would be easier to convert to, but is
not compatible with MPEG2-PS containers in general.  Converting to any
other format would be futile as it would require OCR.

In any case, this is a huge amount of work.  If someone is really
interested, I'd be happy to point them at the relevant specs where I
know them, but there are many more interesting tasks to takle in the
lossless transcoder, so this one isn't on my plate.