[mythtv] MPEG2-MPEG2 transcoding: Illegal video stream

Geoffrey Hausheer mythtv0368 at phracturedblue.com
Fri Mar 3 15:49:41 UTC 2006


On 3/3/06, Thomas Börkel wrote:
> About that --ostream dvd option: IMHO, this should be the default. I
> think, many people cut the video to archive it on DVD. And if not, those
> DVD nav packets would not hurt much, right?
Sure, that is fine for you, but I use mythtranscode for a completely
different purpose, and don't want the NAV packets.  They are not at
all useful for cleaning up ATSC streams.  I'm also going to be adding
code to write out TS/ATSC streams instead of just PS, and the user
will need to select what he wants to do, so this will remain an
option.

> > those look fine.  you need to use --starttime and --chanid instead of
> > --infile if you want to pull the cutlist from the database.
>
> I tried. Still it ignored my cutlist in 0.19.
I can't explain that to you, it works fine here on 0.19, and has since
I released it.  If it works from within mythbackend, it will work from
the command line too.

> I have 3 use-cases besides just watching/deleting the recordings. This
> is how I did before Myth 0.19 (now I can cut with Myth instead of avidemux).
>
> 1.
> A friend missed the show and I want to give it to him. So I just burn it
> to DVD with no cutting. Today I use mpeg2desc, mplex -f 8, dvdauthor,
> growisofs in an automatic script.
This is a case I'd like to be able to support entirely within
mythtranscode at some point.  But again, you are thinking about cases
where you encode the stream yourself.  I want to be able to support
this for DVB/firewire cases too, which makes the problem significantly
more challenging.

>
> 2.
> I want to archive the show and it fits on one DVD. So, I cut it with
> avidemux, save video/audio seperately, convert audio to ac3 with ffmpeg,
> mplex -f 8, dvdauthor/TMPGEnc DVD Author and growisofs. Besides
> avidemux, this is a script.
This will be harder to achieve entirely within mythtranscode, but it
may be doable.  the problem is that mp2 and ac3 use different packet
sizes, so it requires a lot of care to handle properly.  It would also
involve building PES headers for the audio stream, something I don't
do today.  Just for the record, I am not interested in any method that
splits the streams into elementary streams then muxes them together
after processing, it does not work in the general case.  Any solution
to any problem listed has to be able to work within the frame-by-frame
processing that is done by mythtranscode.

>
> 3.
> I want to archive the show, but it is too big. So, I cut it with
> avidemux, save video/audio seperately, tcrequant video, convert audio to
> ac3 with ffmpeg, mplex -f 8, dvdauthor and growisofs. Besides avidemux,
> this is a script.
The audio has the same issue as above, but (depending on how it works)
there is no reason that we couldn't apply something like tcrequant to
the individual frames.  Ths is probably significantly easier than the
audio conversion.

>
> So, since ffmpeg and transcode are already present on Myth boxes,
> mythtranscode could use them.
Transcode isn't present on my myth box (or wasn't until I put it there
to test your case).  ffmpeg isn't normally there either though myth
includes the libav code, so we can perform the same operations ffmpeg
does with some work.

> For my use-cases, it would be perfect, if mythtranscode could convert
> the audio and optionally requant the video. And, as I said above, the
> result should always be DVD compliant.
Again, these could all be options, but there is no 'should always' about it.

>
> Next step would be some DVD mastering code like VDR has, but this is not
> as good as TMPGEnc DVD Author for example, so it is not that necessary
> for me.
Again, it has been discussed, just need someone to do the work.

Basically, there is a whole lot of work needed to implement the above
in mythtranscode, and I don't have sufficient motivation to do it all
(I use mythtranscode primarily to clean up broken streams, and remove
commercials, and have never burned anything I record to DVD).  So I'll
be happy to accept patches, but don't expect massive new features to
just appear out of the blue.

.Geoff


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