[XviD-devel] Display Aspect Ratio -> Pixel Aspect ratio solution

Michael Militzer michael at xvid.org
Sat Dec 13 17:10:41 CET 2003


while I'm not at all familiar how aspect ratios are signaled in the
bitstream, I think it should be possible to scale the output image
within xvidcore without too much overhead: When postprocessing is
switched on, we currently do the following:

1) Copy the internal decoder picture to a seperate buffer
2) Apply postprocessing onto the copied image
3) Do colorspace conversions of the copy and provide the result to
the external app.

Now I think it should be possible to modify step 1 to not only simply
copy the decoder image, but also scale it depending on the AspectRatio.


Quoting Dirk Knop <dknop at stud.uni-goettingen.de>:

> Hi again,
> Christoph Lampert schrieb:
> >Why exactly do you consider this an "abuse"?  I thought that was what PAR
> >is for. 
> >  
> >
> I've done this with a "Display aspect ratio" dropdown listbox now.
> Default is "1:1 (Default)", other options are "4:3 (Anamorph)" and "16:9
> (Anamorph)". This now gets used to calculate the appropiate pixel aspect
> ratio. If this gets accepted by the windows users we can add propietary
> DARs - and maybe even PARs (which will lead to much confusion - as it
> did amongst us as well I think...).
> >I guess it's very often that users who decode and user who encode aren't
> >the same users (What??? How could this happen?), and people playing with
> >broken decoders will of course complain.
> >  
> >
> Yupp. That's a problem i see as well, and why I write now. Now that I
> have that stuff working properly (thanks to Edouard and Radek), we need
> to adopt the DShow filter to read those par, par_width and par_height
> values (or better: let the decoder in core do that) and set the
> according output size (again I think it's more suitable in core).
> What do you think about this?
> >And of course most users don't know what AspectRatio is, even less the 
> >difference between PAR and DAR. 
> >  
> >
> I vote for not letting the user set PAR from VfW. DAR is nearly too much
> already, but then there are some people shouting out for anamorph encoding.
> >Both could be GUI option. Arbitrary values, hm, better hide that very very
> >well.
> >  
> >
> I really would hate to see that as users will find it, no matter how
> well you hide things ;)
> Ok, bottom line: can we add the proper scaling to the core decoder? If
> it would immediatly report the scaled size we wouldn't have to fight
> with problems amongst windows users - i.e. my sample doesn't play
> correctly (here: scaled) with all dshow based players. Don't know what
> this would imply on the *NIX/linux side though.
> Regards
> Koepi
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