[FFmpeg-devel] [PATCHv2 1/2] avdevice/decklink_dec: add support for decoding teletext from 10bit ancillary data

[Reimar Döffinger]

On 19.07.2017, at 18:48, Marton Balint <cus at passwd.hu> wrote:

> 
> On Wed, 19 Jul 2017, John Warburton wrote:
> 
>> On Tue, Jul 18, 2017 at 6:10 PM, Marton Balint <cus at passwd.hu> wrote:
>>> On Sat, 8 Jul 2017, Marton Balint wrote:
>>> 
>>>> This also add supports for 4K DeckLink cards because they always output the
>>>> ancillary data in 10-bit.
>>>> 
>>>> v2:
>>>> - only try teletext decoding for 576i PAL mode
>>>> - some comments as requested by Aaron Levinson
>>>> 
>>>> Signed-off-by: Marton Balint <cus at passwd.hu>
>>> 
>>> Applied the series, thanks for all the comments.
>> 
>> Since this patch was applied, the mingw-w64 compiler, gcc version
>> 6.4.1, fails to link shared library avdevice-57.dll, giving the
>> following error. It is as if the const uint8_t ff_reverse[256] that is
>> found in libavutil/reverse.c somehow isn't being discovered by the
>> linker. I'm afraid my knowledge beyond this point is zero.
>> 
>> libavdevice/decklink_dec.o:decklink_dec.cpp:(.rdata$.refptr.ff_reverse[.refptr.ff_reverse]+0x0):
>> undefined reference to `ff_reverse'
>> collect2: error: ld returned 1 exit status
>> ffbuild/library.mak:101: recipe for target 'libavdevice/avdevice-57.dll' failed
>> make: *** [libavdevice/avdevice-57.dll] Error 1
>> Build failure. Please see error messages above.
> 
> Hmmm. Does adding ff_reverse to the exported symbols in libavutil/libavutil.v fix the problem? Or maybe simply renaming every instance of ff_reverse in the codebase to avpriv_reverse?

Variables/arrays cannot be reliably exported from dynamic libraries and doing so should be avoided.
Even on Linux that leads to "fun" things like copy relocations you really don't want.