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Re: [mythtv-commits] Ticket #2468: Mythtranscode removing audio and subtitles and audio tracks swapping places.
On 10/17/06 05:15, MythTV wrote:

>#2468: Mythtranscode removing audio and subtitles and audio tracks swapping
>places.
>
>Comment (by anonymous):
>
> Replying to [comment:6 ghaushe]:
> > 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

Mike

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Re: [mythtv-commits] Ticket #2468: Mythtranscode removing audio and subtitles and audio tracks swapping places. [ In reply to ]
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.
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Re: [mythtv-commits] Ticket #2468: Mythtranscode removing audio and subtitles and audio tracks swapping places. [ In reply to ]
On Wed, 2006-10-18 at 18:48 -0700, Geoffrey Hausheer wrote:
> 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.

Don't forget the ivtv (PVR-250) driver, which uses it's own format
for embedding EIA-608 captions.

> 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.
Actually, the DVB teletext, DVB VBI, ATSC EIA-708, and ivtv formats
could be embedded in the video stream as user data. The DVB-SUB and
DVD Subtitles can't really be handled that way (you could emboss one
set of subtitles in the video permanently, but this would be ugly.)

> 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.
Yep.

For instance, enabling transcode to a TS format instead of a PS
format is a much more important enhancement and would make
implementing captions and additional language streams much more
doable. Not only could you bring over the captions, subtitles and
additional audio streams, they would also be in a standard format;
this means that it would require no changes in the MythTV video
playback code and they wouldn't require additional ffmpeg hooks.

-- Daniel

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Re: [mythtv-commits] Ticket #2468: Mythtranscode removing audio and subtitles and audio tracks swapping places. [ In reply to ]
On 10/18/06, Daniel Kristjansson wrote:
> Don't forget the ivtv (PVR-250) driver, which uses it's own format
> for embedding EIA-608 captions.
eww..didn't realize that. I'll need to dig up specs on that I guess.

> > 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.
> Actually, the DVB teletext, DVB VBI, ATSC EIA-708, and ivtv formats
> could be embedded in the video stream as user data. The DVB-SUB and
> DVD Subtitles can't really be handled that way (you could emboss one
> set of subtitles in the video permanently, but this would be ugly.)
ATSC can't actually be embedded that way (as it is part of the picture
data and not a seperate stream) well, not in any way that it would be
usable afterward without some post-processing. Embossing isn't really
an option either as the whole point of the lossless transcoder is to
not reencode frames. But yes, all of the text-based streams could be
dealt with in some manner. I was assuming the need for a compliant
format though, which makes it much more work.

> For instance, enabling transcode to a TS format instead of a PS
> format is a much more important enhancement and would make
> implementing captions and additional language streams much more
> doable. Not only could you bring over the captions, subtitles and
> additional audio streams, they would also be in a standard format;
> this means that it would require no changes in the MythTV video
> playback code and they wouldn't require additional ffmpeg hooks.
Yes...This has been near the top of my list for a while. It requires
a sizable amount of change to libreplex though. Once done, it should
be possible to preserve subtitles in whatever format they come down
the stream in (though of course you'll lose them if trying to make a
DVD complaint stream)
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