[FFmpeg-devel] [PATCH 1/2] pixdesc: mark AV_PIX_FMT_PAL8 as having alpha

[Michael Niedermayer]

On Tue, Feb 10, 2015 at 12:20:01PM +0100, wm4 wrote:
> On Mon, 9 Feb 2015 23:49:00 +0100
> Michael Niedermayer <michaelni at gmx.at> wrote:
> 
> > On Mon, Feb 09, 2015 at 10:33:53PM +0100, wm4 wrote:
> > > Otherwise, you could lose the alpha when handling pixel formats in an
> > > opaque manner (i.e. when you don't special-case PAL8).
> > > 
> > > The special case for av_get_pix_fmt_loss()/av_find_best_pix_fmt_of_2()
> > > is now redundant and can be removed.
> > > ---
> > > Fate still passes.
> > 
> > fate fails here
> > make V=2 fate-ac3-2.0
> > TEST    ac3-2.0
> > [...]
> > Assertion (d->nb_components==4 || d->nb_components==2) == !!(d->flags & (1 << 7)) failed at libavutil/pixdesc.c:2097
> > Aborted (core dumped)
> > make: *** [fate-ac3-2.0] Error 134
> > 
> > [...]
> 
> It doesn't fail here, even with the same command.

indeed, re reading the code the call is under
#if defined(ASSERT_LEVEL) && ASSERT_LEVEL > 0


> 
> Anyway, patch dropped, too many problems and inconsistencies. (There's
> probably a lot of code that checks for the number of components
> explicitly. Although the AVPixFmtDescriptor.comp doxygen is completely
> inconsistent with PAL8. Well, whatever.)

I think as is, the best would be to check if any of the 256 entries
has a non 0xFF alpha to find out if theres alpha

If thats insufficient, we could add a 2nd PAL8 pixel format with set
alpha flag to distingish pal8 from transparent pal8

this additional information could be usefull in selecting the
pixel formats in convertion like if RGB24 or RGBA is the optimal
format for a PAL8 source when PAL8 itself cannot be used

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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