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

[Stefan Gehrer]

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?

Stefan