[FFmpeg-devel] [PATCH] reduce global data in lavc

[Michael Niedermayer]

On Wed, Jun 25, 2008 at 01:13:19PM +0200, Stefan Gehrer wrote:
> Michael Niedermayer wrote:
> > On Wed, Jun 25, 2008 at 09:17:44AM +0200, Stefan Gehrer wrote:
> >> Michael Niedermayer wrote:
> >>> On Tue, Jun 24, 2008 at 10:52:34PM +0200, Stefan Gehrer wrote:
> >>>> Stefan Gehrer wrote:
> >>>>> Hi,
> >>>>> After this patch, there are still global variables around
> >>>>> which I would categorize as the following:
> >>>>> 1. run-length tables that I think can be avoided by using
> >>>>>   INIT_VLC_STATIC, but I haven't looked closely.
> >>>>>   These can be found in the following files:
> >>>>>   msmpeg4data.o (rl_table, mv_tables, wmv2_inter_table)
> >>>>>   mpeg12data.o  (ff_rl_mpeg1, ff_rl_mpeg2)
> >>>>>   h263.o        (rl_inter, rl_intra_aic, rl_intra,
> >>>>>                  rvlc_rl_inter, rvlc_rl_intra)
> >>>>>   h261dec.o     (h261_rl_tcoeff)
> >>>>> 2. temporary space for compound literals in many files
> >>>>> 3. ModeAlphabet in vp3.c, which is written to and thus
> >>>>>   should be moved to the context
> >>>> attached patch fixes point 3.
> >>> does that really need to be in the context, isnt the stack enough?
> >> That depends on whether the custom mode alphabet stays
> >> valid only for one frame.
> >>
> >> http://multimedia.cx/vp3-format.txt says:
> >>
> >> " The MB coding mode information is encoded using one of 8 alphabets.
> >> The first 3 bits of the MB coding mode stream indicate which of the
> >> 8 alphabets, 0..7, to use to decode the MB coding information in this
> >> frame."
> >>
> >> The "this frame" sounds like so, but the safe method would be to put
> >> in a test for reusing the custom alphabet in following frames and
> >> run it over the samples we have. Do you think this is necessary, or
> >> can maybe some VP3-pro confirm that the custom alphabet stays valid
> >> only for one frame?
> > 
> > RTFS and tell me how on earth the custom modes of a previous frame could
> > ever be used.
> 
>          if (scheme == 0) {
>              debug_modes("    custom mode alphabet ahead:\n");
>              for (i = 0; i < 8; i++)
>                  s->custom_mode_alphabet[get_bits(gb, 3)] = i;
>          }
> 
> It depends on the bitstream which values of the alphabet are
> overwritten and which are not, or am I missing something?

yes, that the only place using it will only if scheme == 0
and nothing writes to scheme between

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

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