[linux-dvb] Re: AW: Re: AC3 works with Pro7 and PW (was ...towards AC3sound)

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Andreas Vitting wrote:
> 
> The header is wrong !! See at DIGITAL AUDIO COMPRESSION (AC-3) ATSC
> STANDARD. The frames has a exact framesize, starting with a sync sequence.
> Ac3dec works because of his "resync" capability. He does ist for every frame
> again (much work for nothing). Other ac3 decoders only search the first
> sync, check the parameters(framesize, rate and so on) and then playing and
> playing and ....  ;-)
> Ok, i think at the first step you can cut the header away (but the better
> place would be the driver)

I don't think that the driver should strip the PES header, because that's
what VDR needs in order to handle the packets. It's easy for VDR to strip
that header at replay time, and that's what I'm going to do.

Klaus

> 
> Andreas
> 
> -----Ursprüngliche Nachricht-----
> Von: kls@cadsoft.de [mailto:kls@cadsoft.de]Im Auftrag von Klaus
> Schmidinger
> Gesendet: Dienstag, 26. Juni 2001 09:29
> An: linux-dvb@linuxtv.org
> Betreff: [linux-dvb] Re: AC3 works with Pro7 and PW (was ...towards
> AC3sound)
> 
> Stefan.Hagendorn@lindy.cc wrote:
> >
> > Hi all,
> >
> > after applying the patch to strip the header, it is now possible to replay
> > ac3data from Pro7 and from Premiere World. Strangely the header strip is
> > not necessary at Pro7 .. here it works with and without header ... on PW
> > the header must be striped for ac3dec.
> 
> Well, then I guess generally stripping the header in VDR is the way to go.
> I'll change it that way.
> 
> > I'm not an expert regarding mpeg2 .. but striping the PTS should be no
> > problem at all because the external programm cannot sync with the video.
> > Maybe vdr should check the PTS before striping it to get the most possible
> > sync before the stream leaves VDR ?!?!
> >
> > Something like:
> >
> > -analyze pts
> > -sync via pts to video
> > -strip header
> > -send to external pipe
> 
> The data that comes from the driver should already be in sync, so I don't
> know if/how VDR could improve that.
> 
> >From what I've seen so far it looks as if the Dolby Digital data arrives
> somewhere in the area of 1/25 seconds before the video and "normal" audio
> data. However, the test reports here on the list so far have shown that
> the Dolby Digital sound is somewhat "behind" the video. Maybe some of you
> can look further into this and observe whether there is always a constant
> offset (in which direction?) or whether the offset grows/shrinks over time.
> 
> Klaus
-- 
_______________________________________________________________

Klaus Schmidinger                       Phone: +49-8635-6989-10
CadSoft Computer GmbH                   Fax:   +49-8635-6989-40
Hofmark 2                               Email:   kls@cadsoft.de
D-84568 Pleiskirchen, Germany           URL:     www.cadsoft.de
_______________________________________________________________


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