dec_audio, ad_lavc: change license to LGPL

All relevant authors of the current code have agreed.

As always, there are the usual historical artifacts that could be
mentioned. For example, there used to be a large number of decoders
by various authors who were not asked, but whose code was all 100%
removed. (Mostly due to FFmpeg providing all codecs.)

One point of contention is that Nick Kurshev might have refactored the
old audio decoder code in 2001. Basically, there are hints that it might
have been done by him, such as Arpi's commit message stating that the
code was imported from MPlayerXP (Nick's fork), or all the files having
his name in the "maintainer" field. On the other hand, the murky history
of ad.h weakens this - it could be that Arpi started this work, and Nick
took it (and possibly finished it).

In any case, Nick could not be reached, so there is no agreement for
LGPL relicensing from him. We're changing the license anyway, and assume
that his change in itself is not copyrightable. He only moved code, and
in addition used the equivalent video decoder framework (done by Arpi,
who agreed) as template. For example, ad_functions_s was basically
vd_functions_s, which the signature of the decode callback changed to
the same as audio_decode(). ad_functions_s also had a comment that said
it interfaces with "video decoder drivers" (I'm fixing this comment in
this commit).

I verified that no additional code was added that is copyright-relevant,
still in today's code, and not copied from the existing code at the time
(either from the previous audio decoder code or the video framework
code). What apparently matters here is that none of the old code was not
written by Nick, and the authors of the old code have given his
agreement, and (probably) that Nick didn't add actual new code (none
that would have survived), that was not trivially based on the old one
(i.e. no new copyrightable "work").

A copyright expert told me that this kind of change can be considered
not relevant for copyright, so here we go.

Rewriting this would end with the same code anyway, and the naming
conventions can't be copyrighted.

1 files changed, 2 insertions, 2 deletions

diff --git a/Copyright b/Copyright
index 297d37e92c..ce45560154 100644
--- a/Copyright
+++ b/Copyright
@@ -58,9 +58,9 @@ or removed. All new contributions to these files are implied to be LGPLv2.1+.
 LGPL relicensing status:
 
     audio/decode/ad.h               LGPL
-    audio/decode/ad_lavc.c          very hard (nick's changes)
+    audio/decode/ad_lavc.c          LGPL
     audio/decode/ad_spdif.c         LGPL
-    audio/decode/dec_audio.*        very hard (nick's changes)
+    audio/decode/dec_audio.*        LGPL
     audio/filter/af.*               must be killed (main author disagreed)
     audio/filter/af_channel.c       must be killed (main author disagreed)
     audio/filter/af_equalizer.c     must be killed (main author disagreed)