[vdr] Re: I-Frames and cutting

["Dr. Werner Fink" <werner@suse.de>]

On Wed, May 07, 2003 at 12:36:07PM +0200, Wiljo Heinen wrote:
> From: "Dr. Werner Fink" :
> 
> > >
> > > If a GOP is not "closed" _and_ the "broken link" is set, then decoders
> > > should not display the B- and P-frames preceding
> > > the I-frame in time.
> >
> > In other words: the references between frames are given with the relative
> > display time? No sequencial number or something similar?
> >
> 
> I think I do not understand your question :-/ What references between frames
> ?
> 
> The whole point of this closed GOP/broken link thing is that in the
> transmission/file the frames
> are not necessarily appearing in display order.
> 
> Frames are marked with a "temporal offset" value that determines the display
> order of the frames
> in a GOP.
> 
> B-frames "refer" to a preceding P/I and a following P/I. "Preceding" and
> "following" in the stream, not
> regarding to display order. So a B-frame to be displayed after an I-frame
> may occur before the
> I-frame in the stream. Actually this is what happens "normally" in
> DVB-transmissions. It makes life
> of HW-encoders easier. But that way the B-frames refer to a P that is in the
> last GOP. And it may not be
> decoded properly if the preceding GOP is missing.
> 
> Hmm.... I wonder if I made myself clear :-/

OK ... just this in mind, the idea is to convert just _one_ gop
to a sequence of JPEGs or PNMs and original audio/AC3 frames, with the
trick of using those full frames as still framesr Now we could use the DVB
card (via VDR or VDR plugin) for viewing the sequence frame by frame
and set a cut mark.

All JPEGs or PNMs frames together with the appropiate audio/AC3 frames
before the mark should go into a new composed I-frame.

Maybe the GrabImage feature could be used for fetching such a frame sequence
from a gop.

        Werner


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