[linux-dvb] Re: Trying to get a ``polished'' MPEG stream from DVB

[Nyk Tarr <nyk@giantx.co.uk>]

On Thu, May 13, 2004 at 04:25:46PM +0200, Marcus Metzler wrote:
> >>>>> "Måns" == Måns Rullgård <mru@pronto.tv> writes:
> 
>     Måns> Chris Chatfield <C.Chatfield@Teamphone.com> writes:
>     >>> > I can't be the only one trying to transcode DVB output. What
>     >>> does > everyone else do?
>     >>> 
>     >>> I've been playing around with DVB a bit, never had any
>     >>> problems like that.
>     >> I can't offer a solution to the original problem, but at least
>     >> I can explain briefly what's going on - DVB is transmitting
>     >> over the air, and you'd be doing very well to get 100% of the
>     >> TS packets. I suspect the OP had a moment of less than perfect
>     >> reception at that point - hence a missing packet.
> 
>     Måns> This is the reason TS uses fixed-size packets and other
>     Måns> things that make recovery easy.
> 
>     >> Transcode and other mpeg utilities generally expect a perfect
>     >> mpeg stream.  We're not able to supply one unless you convert
>     >> the TS to mpeg with a utility that can cater for unreliable
>     >> input.
>     >> 
>     >> It's worse if you demultiplex the stream into separate audio
>     >> and video streams before transcoding - a loss of a single audio
>     >> frame can play havoc with a/v synchronisation.
> 
>     Måns> Isn't that what PTS is for?
> 
> The problem is that DVD players expect an unbroken stream since a DVD
> is supposed to be mastered from a reliable source. In contrast, DVB
> decoders expect errors and are prepared to correct them.

> Would it be a good idea to insert of drop audio frames in replex to
> avoid PTS inconsitencies? I am not sure how I should fix video frames.
> Any ideas for a consistent strategy?

I think it would be a good idea - it would certainly make re-encoding
much easier. The logical 'filler' video would be to repeat the last
known frame to fill the gap - so it would look like the video had
'frozen'. Audio is more of a problem, or less - silence might be the
only option.

-- 
/__
\_|\/
   /\


-- 
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.