[FFmpeg-devel] ABI break between 3.0 and 3.3 without symvers/SONAME changes

wm4 nfxjfg at googlemail.com
Sat Jun 3 15:12:15 EEST 2017

On Sat, 3 Jun 2017 14:07:30 +0200 (CEST)
Jan Engelhardt <jengelh at inai.de> wrote:

> On Saturday 2017-06-03 13:34, Hendrik Leppkes wrote:
> >On Sat, Jun 3, 2017 at 1:18 PM, Jan Engelhardt <jengelh at inai.de> wrote:  
> >>
> >>The layout of struct AVCodec changed. Four function pointers were
> >>inserted in the middle, shifting void (*flush) to a new address.
> >>The size of AVCodec also changed, which would have required a full
> >>MAJOR bump.  
> >
> >Our ABI is stable in one direction, not in both. [...]
> >The same applies to structs. The size of structs is not  part of the
> >ABI, and as such we are free to grow it to accomodate new fields
> >without breaking the ABI.  
> Size changes are breakers in both directions.
> You claim your ABI is stable in one direction, which means that a 
> program built with 3.0 headers should work with a 3.3 library on a 
> separate system. However, a 3.0 program which invokes 
> someAVcontext->flush(...) would, under 3.3, invoke someAVc->send_frame 
> because of the changed layout. So it's not ABI compatible in that one 
> direction that ffmpeg is supposed to be compile, either.

These callbacks are not public. A program using them is broken.

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