[FFmpeg-devel] swscale / ac3 decoding and lgpl

[Justin Ruggles]

Diego Biurrun wrote:
> On Wed, Feb 25, 2009 at 04:19:04PM -0500, Ronald S. Bultje wrote:
>> from README...
>>
>> * libpostproc and libswscale are distributed under the GNU General Public
>>   License, see the file COPYING.GPL for details. Their compilation and use
>>   in FFmpeg is optional.
>>
>> libswscale is LGPL now, no? Can the README be updated?
> 
> I assume you missed the last round of changes to the README?  I suggest
> you go and read the thread on -cvslog, it contains the answers.
> 
>> Also...
>>
>> * The file libavcodec/ac3dec.c is distributed under the GNU General Public
>>   License.  In order for (E-)AC-3 decoding to work you need to enable GPL
>>   components.
>>
>> What's left to do? Is this documented somewhere? Would be nice to have
>> AC-3 / LGPL decoding.
> 
> Something was said about Walken giving his OK to relicense as LGPL once
> E-AC-3 decoding was supported.  Unfortunately Walken responded at first
> to enquires from Justin and myself but then simply ignored us...

Trying to relicense on our own is a tricky situation, but our AC-3
decoder is significantly different from liba52 now.  The one function
that, to me, looks the same is ac3_decode_transform_coeffs_ch(), which
originally came from liba52/parse.c:coeff_get().

About 4 years ago I wrote an AC-3 frame analyzer that I never released.
I have thought about taking that mantissa decoding function and cleaning
it up, but really the whole thing looks quite awful and slow to me
now...  I can't think of a better or different way to implement the
function cleanly and efficiently other than the one we have currently.

-Justin