Select provider of libav* libraries

[Andreas Cadhalpun]

Hi Reinhard,

On 28.06.2015 21:56, Reinhard Tartler wrote:
> It seems that you have now reimplemented the flavors logic in the ffmpeg package.

Yes.

> Nice.

Well, I'd call it a necessary evil, needed until runtime cpu detection works for
altivec and FFmpeg has a native nb/wb AMR encoder.

> The only thing that I spotted so far is the issue with "libavcodec-extra".

That should be fixed in the current experimental branch by providing a transitional
libavcodec-extra package. Or is there something else?

> I'm not sure if I understand that wiki correctly, but it seems to be that you plan
> on keep on using the package names "libavXXX-ffmpegNN".

Yes, until the next SOVERSION bump or after the next release, whichever comes first.

> That seems unnecessary to me, why wouldn't you want to co stright to libavXXXNN?

I'd want to use those names very much, but I think that wouldn't work well.

> I guess the reason is because that matches the actual soname, that is, libavcodec
> is currently installed with the SONAME "libavcodec-ffmpeg.so".

Yes, the package name should reflect the SONAME, as recommended by policy.

> This is to ensure co-installability with "libav", but do we really need to keep this?

It's also to ensure that packages keep working. See below.

> I think everyone is rather in favor of not having to have both around.

So you think we shouldn't rename the -dev libraries from src:libav/src:libpostproc,
but rather remove these packages after the transition?

> Unless there is a good reason (such as making the transition significantly easier,
> I'd rather avoid those names.

Building a program against the Libav libraries and using it with the FFmpeg libraries
is practically never done, so we'd be the ones to find out how well it works for
most programs.
(Building against FFmpeg and using with these libraries is done by a lot of people
in other distributions, so I'm reasonably sure it works well.)

Actually deb-multimedia.org builds the FFmpeg libraries with the same names as the
Libav ones in the archive and I have seen bug reports that things break.
For example, bug #785650 [1] shows that mpv refuses to work in such a situation:
"mpv was compiled and linked against a mixture of Libav and FFmpeg versions.
This won't work and will most likely crash at some point. Exiting."

Thus we have to treat the FFmpeg libraries as ABI-incompatible to the Libav ones.

Best regards,
Andreas


1: https://bugs.debian.org/785650