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Transcoding and DVB Closed Captioning

 

 

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Niels at Dybdahl

May 23, 2006, 12:05 AM

Post #1 of 9 (3538 views)
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Transcoding and DVB Closed Captioning

Hi,

I have just added a Nova-T to my system (I already have a PVR-250).
Now I have realized that transcoding will remove the closed captioning
DVB-subtitles.
Is there any way to circumvent this?
I am thinking about solutions like:
- "Burning" the subtitles into the video before transcoding
- Splitting the DVB-subtitles (ProjectX?) from the video before transcoding
and somehow merging them afterwards. But maybe the .NUV format does not
support closed captioning subtitles. Could the user jobs be used for this?

HDTV in Europe is based on DVB and MPEG4, so it should be possible to have
MPEG4 and closed captioning subtitles in the same stream.
Has anyone thoughts about this?

Best regards
Niels Dybdahl


robthebob at gmail

May 23, 2006, 5:40 AM

Post #2 of 9 (3463 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

> I am thinking about solutions like:
> - "Burning" the subtitles into the video before transcoding
> - Splitting the DVB-subtitles (ProjectX?) from the video before transcoding
> and somehow merging them afterwards. But maybe the .NUV format does not
> support closed captioning subtitles. Could the user jobs be used for this?

I have been playing around with this and it seems that ProjectX is the
only tool capable of performing this extraction. It's a shame, because
it's really clunky, but I can't find any other way. Once the .sup file
has been output, I am then unable to actually do anything with it -
can't find the tools for that either.

Robin
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Niels at Dybdahl

May 23, 2006, 6:47 AM

Post #3 of 9 (3469 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

On 5/23/06, Robin Neatherway <robthebob [at] gmail> wrote:
>
> > I am thinking about solutions like:
> > - "Burning" the subtitles into the video before transcoding
> > - Splitting the DVB-subtitles (ProjectX?) from the video before
> transcoding
> > and somehow merging them afterwards. But maybe the .NUV format does not
> > support closed captioning subtitles. Could the user jobs be used for
> this?
>
> I have been playing around with this and it seems that ProjectX is the
> only tool capable of performing this extraction. It's a shame, because
> it's really clunky, but I can't find any other way. Once the .sup file
> has been output, I am then unable to actually do anything with it -
> can't find the tools for that either.


So I guess that the closed captioning are lost with MythBurn too, as
MythBurn first demultiplexes and remultiplexes the recording. I wonder if
MythArchive will do it better.
A tool that could "burn" the subtitles into the video would solve the
problems.

Niels Dybdahl


robthebob at gmail

May 23, 2006, 7:39 AM

Post #4 of 9 (3451 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

> A tool that could "burn" the subtitles into the video would solve the
> problems.

If you mean making the subtitles actually part of the video stream,
that wouldn't be a very good solution in the general case surely, as
you dont always want the subtitles. For foreign language with native
subtitles this would be acceptable, but they are often already part of
the video. Or am I misunderstanding your intentions?

Robin
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Niels at Dybdahl

May 23, 2006, 8:13 AM

Post #5 of 9 (3476 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

On 5/23/06, Robin Neatherway <robthebob [at] gmail> wrote:
>
> > A tool that could "burn" the subtitles into the video would solve the
> > problems.
>
> If you mean making the subtitles actually part of the video stream,
> that wouldn't be a very good solution in the general case surely, as
> you dont always want the subtitles. For foreign language with native
> subtitles this would be acceptable, but they are often already part of
> the video. Or am I misunderstanding your intentions?


Foreign movies sent via DVB-T in Denmark only have subtitles via a separate
DVB-stream.
So making the subtitles part of the video stream would definitely make it
easier for me: MythBurn would still work, Transcoding would still work.
But I have not found any tools capable of burning the subtitles into the
videostream.
There are tools that can demultiplex (ProjectX) the subtitles into a .sup
format which some dvd-authoring applications can accept, and maybe
MythArchive will handle converting to DVD-format, but transcoding is still a
problem.
I was looking forward to DVB-T because I thought it would make transcoding
better (less noise). But now I can only use transcoding for native shows.
Actually I have started to force foreign shows to my analog card, so that I
still can transcode them.

Best regards
Niels Dybdahl


mythtv at dsl

May 23, 2006, 8:16 AM

Post #6 of 9 (3475 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

Niels Dybdahl wrote:
> On 5/23/06, *Robin Neatherway* <robthebob [at] gmail
> <mailto:robthebob [at] gmail>> wrote:
>
> > I am thinking about solutions like:
> > - "Burning" the subtitles into the video before transcoding
> > - Splitting the DVB-subtitles (ProjectX?) from the video before
> transcoding
> > and somehow merging them afterwards. But maybe the .NUV format
> does not
> > support closed captioning subtitles. Could the user jobs be used
> for this?
>
> I have been playing around with this and it seems that ProjectX is the
> only tool capable of performing this extraction. It's a shame,
> because
> it's really clunky, but I can't find any other way. Once the .sup file
> has been output, I am then unable to actually do anything with it -
> can't find the tools for that either.
>
>
> So I guess that the closed captioning are lost with MythBurn too, as
> MythBurn first demultiplexes and remultiplexes the recording. I wonder
> if MythArchive will do it better.
> A tool that could "burn" the subtitles into the video would solve the
> problems.
>
> Niels Dybdahl
>
Have you had a look at spumux which is part of dvdauthor? It can create
the subtitle stream needed when creating a DVD. It can use both text
based subtitles as well as image based. I'd love to add subtitle support
to MythArchive but there is quite a lot of work involved in getting that
to work and isn't something I need myself so isn't a high priority. If
someone wants to take a look I may be able to provide some assistance.
The difficult bit is getting the subtitles into a form that can be used
by spumux.

http://dvdauthor.sourceforge.net/doc/spumux.html

Paul H.


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Niels at Dybdahl

May 23, 2006, 9:09 AM

Post #7 of 9 (3453 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

>
> Have you had a look at spumux which is part of dvdauthor? It can create
> the subtitle stream needed when creating a DVD. It can use both text
> based subtitles as well as image based. I'd love to add subtitle support
> to MythArchive but there is quite a lot of work involved in getting that
> to work and isn't something I need myself so isn't a high priority. If
> someone wants to take a look I may be able to provide some assistance.
> The difficult bit is getting the subtitles into a form that can be used
> by spumux.
> http://dvdauthor.sourceforge.net/doc/spumux.html


Thanks for the tip. I have looked at it and done some surfing.
There are existing scripts like:

http://www.guru-group.fi/~too/sw/m2vmp2cut/pxsup2dast.py

which can create an xml file for dvdauthor from a .sup file (subtitles
stream file) created by ProjectX. So it seems straightforward to build this
into MythBurn.
I have read from other sources that there might be problems with the colors
of the subtitles, but that can be handled by editing the associated .ifo
file.

Best regards
Niels Dybdahl


robthebob at gmail

May 24, 2006, 6:41 AM

Post #8 of 9 (3439 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

On 5/23/06, Niels Dybdahl <Niels [at] dybdahl> wrote:
> Thanks for the tip. I have looked at it and done some surfing.
> There are existing scripts like:
>
> http://www.guru-group.fi/~too/sw/m2vmp2cut/pxsup2dast.py
>
> which can create an xml file for dvdauthor from a .sup file (subtitles
> stream file) created by ProjectX. So it seems straightforward to build this
> into MythBurn.

Do you want to keep the subtitles graphical, or convert them to text?
I think I have a conversion process worked out to get them to text
which I am going to try some more later on today:

DVB-->(ProjectX)-->.SUP-->(pxsup2dast)-->pngs+spuxml-->(convert)-->pgms+spuxml-->(pgm2txt/gocr+convert
spuxml to .srtx)-->.txts+.srtx-->(srttool)-->.srt

Bit wacky, but I think it'll work. Going to vobsub would probably be
preferable, so if you see how that could happen, please say.

Robin
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Niels at Dybdahl

May 24, 2006, 7:10 AM

Post #9 of 9 (3460 views)
Permalink
Re: Transcoding and DVB Closed Captioning [In reply to]

>
> Do you want to keep the subtitles graphical, or convert them to text?


As long as I can view the subtitles I do not care if they are stored
graphical or as text.
But I guess storing them graphical will be easiest in the long run as they
are graphical in the DVB and DVD formats and MythTV is already able of
displaying graphical subtitles

I think I have a conversion process worked out to get them to text
> which I am going to try some more later on today:
>
>
> DVB-->(ProjectX)-->.SUP-->(pxsup2dast)-->pngs+spuxml-->(convert)-->pgms+spuxml-->(pgm2txt/gocr+convert
> spuxml to .srtx)-->.txts+.srtx-->(srttool)-->.srt


I also found a OCR script for converting to .srt. But apparently it require
some training of the OCR part.

Bit wacky, but I think it'll work. Going to vobsub would probably be
> preferable, so if you see how that could happen, please say.


vobsub seems to accept .srt files, so I guess your workflow above should
work.
For burning DVD, the following workflow should work:

MythBurn:
MPG --->(ProjectX)---> M2V, MP2, SUP,IFO --->(mplex)---->MPG, SUP,IFO--->
(pxsup2dast.py <http://www.guru-group.fi/%7Etoo/sw/m2vmp2cut/pxsup2dast.py>
)--->MPG,XML,PNG--->(dvdauthor)---->VOB,IFO

For transcoding, it would probably be easiest to cut the SUP,IFO files out
of the MPEG2s (might be doable with ProjectX as a user job) and either keep
them as separate files or somehow merge them with the transcoded MPEG4 file
(The "Nero Digital" format is a MPEG4 format that can contain subtitles), so
there is no doubt that it can be done, but it might be easier to keep them
as separate files (as the thumbnails already are).
If the MPEG2 and MPEG4 decoders for the internal player share a lot of code,
it might not be too difficult as the MPEG2 decoder already can handle a
subtitle stream.

Best regards
Niels Dybdahl

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