[FFmpeg-devel] Bug report : build problem with "configure --disable-encoders"

Michael Niedermayer michaelni
Mon Nov 24 23:50:24 CET 2008

On Mon, Nov 24, 2008 at 05:24:40PM +0100, Diego Biurrun wrote:
> On Mon, Nov 24, 2008 at 03:08:06PM +0100, David Geldreich wrote:
> >
> > Le 24 nov. 08 ? 11:08, Michael Niedermayer a ?crit :
> >
> >> On Mon, Nov 24, 2008 at 09:56:21AM +0100, Diego Biurrun wrote:
> >>> On Sat, Nov 22, 2008 at 03:25:47PM +0100, David Geldreich wrote:
> >>>>
> >>>> As it was originally in the mpegvideo_enc.c file I thought that it
> >>>> make sense to move it to mpegvideo.c, if it is a bad idea what would
> >>>> you propose to make --disable-encoders or --disable-decoders to  
> >>>> work ?
> >>>
> >>> Michael, which file do you want?
> >>
> >> aandcttab.c/h
> >
> > Attached a patch using aandcttab.c/h to solve this --disable- 
> > encoders/--disable-decoders issue.
> >
> > As I am new to ffmpeg, I have some naming/comment/doc issue :
> >
> > 1) I copied the copyright from another file but do not know exactly what 
> > to put in it
> The way you did it is right.

> > 2) I do not exactly know what these aanscales table are for, so it is  
> > hard to put a "correct" doxygen comment for the file content
> Dunno, Michael?

the AAN (arai agui nakajima) (I)DCT tables are for AAN style dcts, these dcts
have their arithemtic operations reordered so that a bunch of multiplications
from the row and column pass can be merged together and then also merged
into the quantization / dequantization in some cases.
The big problem with these (I)DCTs is that they are nummerically not very
precisse when implemented with fixed point arithmetic ...

also about the patch ...
dependancies really are
various en/decoders [mpeg1/2/4 ...] depend on at least one idct
various encoders [mpeg1/2/4 ...] depend on at least one dct
we have many dcts and idcts (and currently no way to disable any)
if an AAN style (I)DCT is enabled then these AAN tables will be needed
thus it is not strictly correct to add these tables to all the encoders.
though the correct soluttion might need quite a bit of work

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In fact, the RIAA has been known to suggest that students drop out
of college or go to community college in order to be able to afford
settlements. -- The RIAA
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