Re: [libdv-dev] Possible bug encoding interlaced material?

[Stefan L. <st...@lu...>]

On Mittwoch, 6. April 2005 06:10, Jonathan Woithe wrote:
> Hi Stefan

> > To my opinion there are to issues:
> > 1. block artefacts in luma space. If noticed them too, even after first
> >    recoding of the same frame with libdv.
> > 2. shadows of the other field. This may be related to color handling of
> >    other decoders too. As you encode with fps=25 I think you are
> >    operating in PAL mode. You converted dv to png with mplayer who
> >    uses ffmpeg to my knowledge as default decoder.
> >    DV-PAL has different needs when 4:2:0 is decoded as color subsampling
> >    is field based and not frame based.
> 
> Yes, I am in PAL land (Australia to be precise).  I can also confirm that
> the default decoder in mplayer is ffmpeg.
> 
> I did some further tests overnight which might be interesting.  These
> involved using ffmpeg's encoder to see what it did.  The updated results
> are at the bottom of
> 
>   http://www.atrad.com.au/~jwoithe/mpeg/pantest/
> 
> Essentially I tested ffmpeg's encoder both with a CGI frame and a "real
> world" frame.  The upshot was that with the real world frame ffmpeg's encoder
> appears to do a good job, while with the CGI input it's better than libdv but
> there are still issues.  Note though that these issues might be associated
> with the limits of DV's quality - I don't know and can't test this.
> 
> Getting back to your comment about there being possibly two issues, I'm not
> sure I understand what you're suggesting.  In (1) are you saying that libdv
> is having trouble keeping luma information block-free and that this has been
> noticed at other times?  My understanding of (2) is that perhaps libdv's PAL
> encoder (and maybe its decoder as well) is not as well tested as the NTSC
> side of things and that it might still have gremlins lurking in it, and that
> these problems might affect ffmpeg's decoder as well?

to (1): Yes, I tried to fix that, but I _failed_.  So it is still on the TODO list.
to (2): There was a big thread on this list. It started on 2003-11-01,
          subject: "libdv produces strange interlaced frames".
          Mails from Roman's and me (2003-11-06/07) show the handling
          of field based chroma information. This is implemented in libdv's
          decoder for YUV2 output (not encoding part).

-- 
Stefan Lucke