Select provider of libav* libraries

[Andreas Cadhalpun]

Hi Reinhard,

On 06.06.2015 20:30, Reinhard Tartler wrote:
> On Sat, Jun 6, 2015 at 1:51 PM, Bálint Réczey <balint at balintreczey.hu> wrote:
>>> The problem is that Debian users must be allowed to redistribute it,
>>> but as far as I understand it, it is not allowed to distribute e.g.
>>> a live DVD with hedgewars and libavcodec-extra installed.
>>> I also pointed this out in the previous discussion [1].
>> I'm not absolutely sure, but IMO yes, such Live DVD-s would not be
>> allowed, but it is a problem of live DVD makers to care about. Package
>> maintainers can't and should not prevent this usage.
> 
> Why would you think that distributing the packages libavcodec-extra
> and hedgewars on the same Live media would create a derived work that
> must fulfill all licenses?
> 
> I fail to spot the problem here.

The problem I see is run-time linking a GPLv2-only program with a GPLv3+
library. I think this makes such a Live DVD undistributable, because the
licenses are not compatible.

> If you want to be extra careful, just install the regular GPLv2+
> libavcodec package, which according to the dependencies of the
> hedgewars package should work just fine.

This wouldn't work if you also want to install devede, which depends
on libavcodec-extra. (This dependency should probably be a recommends 
at most, anyway.)

>>>> Since the hassle makes more work for active ffmpeg maintainers and
>>>> while I sponsored a few uploads I don't consider myself one I should
>>>> not make the call, but it would be really nice to provide the AMR
>>>> encoder as well in Debian and also keeping hedgewars in the archive.
>>>>
>>>> Maybe there is a way of providing libavcodec-extra and having modern
>>>> packaging scripts. Maybe patching the build could help, but I have not
>>>> checked this idea.
>>>
>>> The AMR encoder is anyway just a wrapper around libopencore/libvo.
>>> Gstreamer also has similar wrappers and since they are plugins, the
>>> license is less of a problem.
>>> Thus anyone really wanting to encode AMR can use gstreamer.
> 
> Except those that want or need to use the "avconv" or "ffmpeg"
> command-line utilities.

How many would that be?

>> I'm OK with disabling AMR encoder in ffmpeg and stay GPLv2 compatible
>> with the packages since I have no packages requiring it nor use-cases
>> as a user requiring it, but I prefer the choice provided by by current
>> libav packaging.
> 
> Thanks for the support!
> 
>> Would it be hard to patch the build system?
> 
> To do what exactly?

To implement this in a dh7-style debian/rules file.

> The current libav packaging already implements
> this in a way that the user can choose what packages to install.
> 
> On a personal note: The libav packaging can surely be improved and
> simplified. But throwing away years of work just because, and knowing
> about the regressions for the sake of simplicity feels wrong.

The main modernization would be a rewrite of the debian/rules file
in dh7-style. This naturally replaces the previous one.
The rest of the packaging is mainly declarative and can't be varied
that much anyway.

Not having the libavcodec-extra flavor is not only a regression
(having no AMR encoder), but also an improvement (simpler debian/rules,
no license incompatibility to worry about, faster build, ...).
I happen to think the improvement factor is bigger than the regression
factor, but others may disagree.

Best regards,
Andreas