Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries

[Andreas Cadhalpun]

Hi Guillem,

On 29.06.2015 18:01, Guillem Jover wrote:
> [ First of all, thanks for providing a ffmpeg version of the package,
>   there's quite some media that does not play correctly with libav. ]

Credits for that go to Alessandro.
(We plan to transition all packages from Libav to FFmpeg soon, see [1].)

> The mpv program emits the following warning on startup:
> 
> ,---
> Warning: mpv was compiled against a different version of ffmpeg than the shared
> library it is linked against. This can expose subtle ABI compatibility issues
> and can lead to misbehavior and crashes.
> `---

I guess this warning is meant as sanity check for those compiling mpv themselves.
(The ffmpeg binary also checks for matching compile-time and run-time libraries.)
These warnings aren't very useful in a distribution, where package dependencies
ensure ABI compatibility.

> Which, to me points out there's a problem somewhere. Either:
> 
>  * the warning is bogus, and
>    - mpv should be silenced in common/av_log.c:print_libav_versions, or

If the warning bothers you, this would be the way to go.

>    - ffmpeg should not be exposing the minor versions in its macros
>      and *_version() functions, so that such warnings do not trigger, or

The minor versions are used to e.g. indicate new features, so that programs
can do exact compile-time checks. Not exposing them would break that.

>  * the warning is valid, and
>    - mpv needs a strict versioned dependency, or

The dependencies are calculated by the symbols mechanism. No stricter
dependencies should be necessary.

>    - mpv very unfortunately needs to statically link against ffmpeg, or

Not that, please!

>  * something else?
> 
> I'm filing it here, because it's not clear to me where the real
> problem lies. Please reassign as appropriate if need be.

I think you were right to file this bug against mpv.

Best regards,
Andreas


1: https://wiki.debian.org/Debate/libav-provider/ffmpeg