[XviD-devel] Buggy Divx5?

[Michael Militzer]

Hi,

> On Sat, 2 Nov 2002, Michael Militzer wrote:
>
> > Hi,
> >
> > ----- Original Message -----
> > From: "Christoph Lampert" <chl@math.uni-bonn.de>
> > To: <xvid-devel@xvid.org>
> > Sent: Saturday, November 02, 2002 3:10 PM
> > Subject: [XviD-devel] Buggy Divx5?
> >
> >
> > > Hi,
> > >
> > > my GMC works now, but I have a problem with the combination
> > >
> > > quarterpel+inter4v+GMC when decoding with DivX5(divx4linux-20020418)
> > >
> > > It seems that inter4v blocks are positions incorrectly (just a guess).
> > >
> > > All other combinations work, and decoding with ffmpeg works, too.
> > > Do you know if this is a DivX5-bug?
> >
> > yes, it is imho. qpel+inter4v does not work with DivX5 (but perfectly
with
> > ffmpeg and ms-fdam)
>
> You are right, I forgot to check without GMC. So it's just qpel+inter4v,
> I should have noticed earlier.
>
> Btw. do you know what causes it (what the bug is)? Then we might add a
> "workaround" mode. I think compatability to DivX5 (even if that is
> buggy) is still important to many users.

I don't really know why DivX5 cannot correctly decode INTER4V+qpel vids, but
anyway it makes no sense at all to imitate DivX bugs (and generate
non-compliant videos then) just to make XVID output playable with DivX (and
I hope you weren't really considering this option). Simple solution is to
not use 4MV mode, but those videos still won't play correctly with DivX5
because of DivX's wrong chroma rounding...

So you see it's not that easy (nor reasonable) to try to introduce special
"compatibility modes" into the XVID encoder. It's true that surely a lot of
people would like to play their XVID videos with DivX as well, but if DivX
isn't really MPEG-4 compliant (and therefore cannot play XVID videos) that's
not our fault. I'd vote to not care about DivX compatibility, our goal
should be plain and simple: standard compliance. Sure, XVID encoded material
might not play correctly with DivX then, but I'm sure that the DivX guys
will fix their decoder bugs sooner or later (and I'd bet that a bugfixed
DivX will be released quicker if we don't implement a DivX compatibility
mode).

bye,
Michael