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

Michael Niedermayer michaelni
Wed Jun 25 12:54:01 CEST 2008

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.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Old school: Use the lowest level language in which you can solve the problem
New school: Use the highest level language in which the latest supercomputer
            can solve the problem without the user falling asleep waiting.
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