[vdr] Re: vdr cuts recordings with ugly artifacts at cutting-points

[Sergei Haller <Sergei.Haller@math.uni-giessen.de>]

On Wed, 16 Apr 2003, Stefan Huelswitt (SH) wrote:

SH> On 16 Apr 2003 Sergei Haller <Sergei.Haller@math.uni-giessen.de> wrote:
SH> > On Wed, 16 Apr 2003, Stefan Huelswitt (SH) wrote:
SH> >
SH> > SH> The topic "broken link" only applies to video packets and tells
SH> > SH> the decoder to skip some frames.
SH> > SH> This totaly different from the audio packet problem.
SH> >
SH> > consider following stream:
SH> >
SH> >   video:   123456789
SH> >   audio:     123456789
SH> >
SH> > if  you just mark the frames 5,6,7 as "broken", (without removing anything
SH> > from the stream) what exactly will be dropped?
SH>
SH> It's a bit different (AFAIK).
SH>
SH> What you are refering as 5,6,7 in the video stream are not
SH> frames, these are packets, which each contains a GOP (group of
SH> pictures). Every GOP consists of several video frames (I,B,P),
SH> usually 12. You can mark a GOP as broken, but not packets or
SH> individual frames

Well. I just simplified the thing a bit. What I was referring to by frames
5,6,7 was a whole GOP.

Well.  Let  me  formulate  my  question  in  a  different way: Imagine the
following  stream,  where p1, ..., p9 are packets, each of them containing
one GOP and several audio frames. Is it correct so far?

stream:   .... p1 p2 p3 p4 p5 p6 p7 p8 p9 .....

the length of the video frames of one GOP is 12/25 = 0.48s = 480ms right?

The audio is delayed by about 400ms (I read this in other postings).

This  means that the audio frames, which belong to the video frames in GOP
of  the  packet p5, are partially in the packet p5 and partially in p6. Is
it correct so far?

So  now  I  want  to  cut  the stream and to keep all the video until (and
including) the GOP of the package p5 and of course the corresponding audio
frames:
 -  I  could  just  throw away all packages starting with p6. But then, of
    course,  some  of  the  audio  frames are missed. So that's, where the
    problem begins.

 -  Now I want to try a different approach:  I  throw away all the packets
    beginning with p7 --- then I have all audio frames  I need, But I have
    one GOP of video, which I don't need.

 -  Now I mark the GOP of the package p6 as "broken".
    Thus I have the video stream until (and including) the GOP of package
    p5. And I have all the Audio frames which correspond to the frames of
    the GOP of p5.
                       --- or did I miss something here? ---

c ya
        Sergei
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