Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Control: tags -1 fixed-upstream On Mon, Jun 29, 2015 at 06:01:04pm +0200, Guillem Jover wrote: Package: mpv Version: 0.9.2-1+ffmpeg Severity: normal Hi! [ First of all, thanks for providing a ffmpeg version of the package, there's quite some media that does not play correctly with libav. ] 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. `--- 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 Upstream removed the warning now, see [0]. Cheers [0] https://github.com/mpv-player/mpv/commit/5594379b27f3c19a475b83a001a1cd96946c signature.asc Description: Digital signature
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Control: forwarded -1 https://github.com/mpv-player/mpv/issues/2110 Sorry for the delay. On mer, lug 01, 2015 at 10:35:13 +0200, Andreas Cadhalpun wrote: Hi Guillem, On 30.06.2015 23:14, Andreas Cadhalpun wrote: On 30.06.2015 21:40, Guillem Jover wrote: Perhaps, but the comment at http://sources.debian.net/src/mpv/0.9.2-1%2Bffmpeg/common/av_log.c/#L229 was not very soothing, so that was one additional reason for the bug. :) Hmm, this comment is indeed a bit worrisome. But I'm not sure I understand the reasoning given there. As far as I know the accessor functions are only necessary for API that is not present in Libav (in order to be ABI compatible after Libav merges, as the comment says). So whether or not one uses the accessors shouldn't make a difference for compatibility with Libav. I've investigated this a bit more and it seems that the only potentially problematic FFmpeg-only API used by mpv is AVFrame-metadata, which mpv accesses via av_frame_get_metadata. [1] Thus I think the comment is just wrong and the warning should be removed. If I understand the comment correctly, the problem isn't so much ffmpeg-only APIs like -metadata, but the fact that mpv doesn't use accessor functions for struct fields provided by ffmpeg to maintain ABI compatibility because libav doesn't have those functions (but it still has the structs). IMO the warning can be removed in the Debian packages because it's fairly annoying and mostly useless (it's not like Debian users can do anything about it besides recompiling the package), but maybe we should better investigate this alleged ABI compatibility problem in ffmpeg. For example the upstream-tracker thingy shows several ABI changes introduced in ffmpeg 2.5 (e.g. new fields in the middle of structs) without a SONAME bump: http://upstream.rosalinux.ru/versions/ffmpeg.html The mpv Debian package could also start using the accessors that ffmpeg provides but only when built with ffmpeg (which should hopefully become the default soonish), but tracking down where these accessors should be used is probably going to be a bit of a pain. Cheers signature.asc Description: Digital signature
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Hi Alessandro, On 07.07.2015 17:26, Alessandro Ghedini wrote: On mer, lug 01, 2015 at 10:35:13 +0200, Andreas Cadhalpun wrote: I've investigated this a bit more and it seems that the only potentially problematic FFmpeg-only API used by mpv is AVFrame-metadata, which mpv accesses via av_frame_get_metadata. [1] Thus I think the comment is just wrong and the warning should be removed. If I understand the comment correctly, the problem isn't so much ffmpeg-only APIs like -metadata, but the fact that mpv doesn't use accessor functions for struct fields provided by ffmpeg to maintain ABI compatibility because libav doesn't have those functions (but it still has the structs). That wouldn't make much sense. If it is safe to access a struct member in Libav, it is also safe to access it in FFmpeg. In that case there is no need for accessor functions. These are either also necessary (and present) in Libav, or it is an FFmpeg-only API like AVFrame-metadata. IMO the warning can be removed in the Debian packages because it's fairly annoying and mostly useless (it's not like Debian users can do anything about it besides recompiling the package), but maybe we should better investigate this alleged ABI compatibility problem in ffmpeg. These changes in private ABI are well-known and caused by merges from Libav: In FFmpeg some structs have more members than in Libav. If there is a new member added at the end of the struct in Libav, it is inserted in the middle of the struct in FFmpeg. Thus all FFmpeg-only struct members must never be accessed directly. (This is documented very clearly.) For example the upstream-tracker thingy shows several ABI changes introduced in ffmpeg 2.5 (e.g. new fields in the middle of structs) without a SONAME bump: http://upstream.rosalinux.ru/versions/ffmpeg.html Yes, e.g. the framerate and initial_padding members were added to the end of AVCodecContext in Libav and merged into FFmpeg between 2.4 and 2.5. The mpv Debian package could also start using the accessors that ffmpeg provides but only when built with ffmpeg It already does exactly that! ;) (which should hopefully become the default soonish), but tracking down where these accessors should be used is probably going to be a bit of a pain. Since this only affects FFmpeg-only struct members and mpv is also compatible with Libav, thus using ifdeffery for FFmpeg-only functionality, finding the potentially problematic case(s) is not that hard. There is only AVFrame-metadata, which is accessed correctly. Best regards, Andreas -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Hi Guillem, On 30.06.2015 23:14, Andreas Cadhalpun wrote: On 30.06.2015 21:40, Guillem Jover wrote: Perhaps, but the comment at http://sources.debian.net/src/mpv/0.9.2-1%2Bffmpeg/common/av_log.c/#L229 was not very soothing, so that was one additional reason for the bug. :) Hmm, this comment is indeed a bit worrisome. But I'm not sure I understand the reasoning given there. As far as I know the accessor functions are only necessary for API that is not present in Libav (in order to be ABI compatible after Libav merges, as the comment says). So whether or not one uses the accessors shouldn't make a difference for compatibility with Libav. I've investigated this a bit more and it seems that the only potentially problematic FFmpeg-only API used by mpv is AVFrame-metadata, which mpv accesses via av_frame_get_metadata. [1] Thus I think the comment is just wrong and the warning should be removed. Best regards, Andreas 1: https://sources.debian.net/src/mpv/0.9.2-1%2Bffmpeg/video/filter/vf_lavfi.c/#L309 -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Hey! On Mon, 2015-06-29 at 21:45:26 +0200, Andreas Cadhalpun wrote: (We plan to transition all packages from Libav to FFmpeg soon, see [1].) Yeah, I'm aware, eagerly waiting it! On 29.06.2015 18:01, Guillem Jover wrote: 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. Perhaps, but the comment at http://sources.debian.net/src/mpv/0.9.2-1%2Bffmpeg/common/av_log.c/#L229 was not very soothing, so that was one additional reason for the bug. :) 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. It's not so much that it bothers me; as I've mentioned, either the warning is valid and there's a potential ABI problem, or it is not and then emitting an alarming message that the user can hardly fix on each invocation might be slightly taxing, it is at least a sure way to train users to ignore valid ones. :) - 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. How does the libav project handle this? I don't remember seeing such warning with an mpv compiled against that. * the warning is valid, and - mpv needs a strict versioned dependency, or The dependencies are calculated by the symbols mechanism. Sure. No stricter dependencies should be necessary. In principle, but I was going by the comment on that source file. Sorry, I should have provided a direct link initially. - mpv very unfortunately needs to statically link against ffmpeg, or Not that, please! Well, I abhor such kind of solutions with a passion, but if there's no better option… Thanks, Guillem -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Hi Guillem, On 30.06.2015 21:40, Guillem Jover wrote: On Mon, 2015-06-29 at 21:45:26 +0200, Andreas Cadhalpun wrote: (We plan to transition all packages from Libav to FFmpeg soon, see [1].) Yeah, I'm aware, eagerly waiting it! :) On 29.06.2015 18:01, Guillem Jover wrote: 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. Perhaps, but the comment at http://sources.debian.net/src/mpv/0.9.2-1%2Bffmpeg/common/av_log.c/#L229 was not very soothing, so that was one additional reason for the bug. :) Hmm, this comment is indeed a bit worrisome. But I'm not sure I understand the reasoning given there. As far as I know the accessor functions are only necessary for API that is not present in Libav (in order to be ABI compatible after Libav merges, as the comment says). So whether or not one uses the accessors shouldn't make a difference for compatibility with Libav. 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. It's not so much that it bothers me; as I've mentioned, either the warning is valid and there's a potential ABI problem, or it is not and then emitting an alarming message that the user can hardly fix on each invocation might be slightly taxing, it is at least a sure way to train users to ignore valid ones. :) Indeed. In this case clarifying with upstream what this warning means, i.e. which accessors are not used, would be good. - 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. How does the libav project handle this? Identically. I don't remember seeing such warning with an mpv compiled against that. The Libav project has only made new releases about once a year, usually with a SONAME bump, so that mpv got recompiled. A binNMU would make the warning go away. * the warning is valid, and - mpv needs a strict versioned dependency, or The dependencies are calculated by the symbols mechanism. Sure. No stricter dependencies should be necessary. In principle, but I was going by the comment on that source file. Sorry, I should have provided a direct link initially. Yes, that comment is important. - mpv very unfortunately needs to statically link against ffmpeg, or Not that, please! Well, I abhor such kind of solutions with a passion, but if there's no better option… The better solution would be to use the API as documented, i.e. with the accessor functions. In particular because I don't see a reason not to do that. Best regards, Andreas -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
Package: mpv Version: 0.9.2-1+ffmpeg Severity: normal Hi! [ First of all, thanks for providing a ffmpeg version of the package, there's quite some media that does not play correctly with libav. ] 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. `--- 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 - ffmpeg should not be exposing the minor versions in its macros and *_version() functions, so that such warnings do not trigger, or * the warning is valid, and - mpv needs a strict versioned dependency, or - mpv very unfortunately needs to statically link against ffmpeg, or * 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. Thanks, Guillem -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Bug#790446: mpv: Warning about mismatch between build and run-time ffmpeg libraries
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 -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
