[mythtv-users] Solved: CC (and maybe Teletext) to DVD

[Anthony Zawacki]

faginbagin wrote:
>>> Anyway, I have come up with an alternative approach. I've tinkered with
>>> mythburn.py (the 0.20.2 version). One of the things I've done is to
>>> create chapter marks using the commercial marks mythcommflag stores in
>>> the database. As a result, you can use your DVD remote's skip buttons to
>>> bypass the commercials. I'm planning to include a patch for anyone who's
>>> interested. I skimmed the latest code in trunk, and I think there's a
>>> good chance my patch might apply cleanly to the latest mythburn.py
> 
>> Using this information, shouldn't it be possible to create the dvd in a
>> way that the default movie would then automatically skip the commercials
>> by arranging the chapter order?  You would still have the commercials on
>> the dvd in unreferenced chapters, but you would still get captions and
>> the movie would play straight through.
> 
> That's a thought, although I'm not sure it can be done with dvdauthor.
> Maybe some other tool?

Unfortunately, I don't have a direct example, but I believe that it is 
possible.  It should be able to be done using the <pre> or <post> tags 
for the <pgc>.

> Another thought I had would be to cut commercials from the "final.mpg"
> created after the CC based subtitle stream has been added. I don't know
> if a mythtv utility can do this and preserve the subtitles, but perhaps
> another tool, combined with a SQL query of the mythtv database to get
> the commercial marks?

I'm less familiar with how captions work than mpeg files in general. 
However, when I get home tonight, I will experiment with gopchop to see 
if captions survive cutting out commercials with it.  The last time I 
looked at gopchop, it didn't support EDLs (Edit Decision Lists, which is 
essentially the list of commercials to be cut) but that was quite some 
time ago.

> FWIW, the IVTV VBI data stream headers have their own time base, very
> different from the time base of the video and audio streams. I suspect
> the tools that demux and remux the video and audio streams aren't using
> the time stamps in MPEG2 stream headers. At least, they don't look like
> consistent sources of time stamps. I suspect the tools rely more on
> frame counts and fps. That's one reason why I think doing commercial
> cutting using the original recording would be tricky. So far, I've only
> figured out how to decode the stream headers, not the stream data, so I
> have no idea where frames begin and end.

My understanding, in a simplistic manner, is that MPEG has a Group Of 
Pictures (GOP) which basically is a frame that is the complete picture, 
and then a series of diffs to this first frame.  So, if you cut on a GOP 
marker, you can cut from there to the next GOP marker losslessly.  But 
how the subtitles are folded into the GOPs, I don't know.  I'm fairly 
confident that some subtitles will survive cutting a recording using 
gopchop.  I'm not confident in what the result will be as I could see 
several different possibilities, worse case the subtitles are not cut, 
and they get further and further off with each subsequent cut in the 
video stream.

Anthony