ffmpeg and zlib support

[velorom]

I trying to install FFmpeg on Windows 10, VS2017.
FFmpeg compiled and installed normally, but there is no zlib support.
I tried to dig config.log of FFmpeg and found these lines:

check_pkg_config zlib zlib zlib.h zlibVersion
test_pkg_config zlib zlib zlib.h zlibVersion
false --exists --print-errors zlib
check_lib zlib zlib.h zlibVersion -lz
check_func_headers zlib.h zlibVersion -lz
test_ld cc -lz
test_cc
BEGIN ./ffconf.o2M6qpqs/test.c
    1	#include <zlib.h>
    2	#include <stdint.h>
    3	long check_zlibVersion(void) { return (long) zlibVersion; }
    4	int main(void) { int ret = 0;
    5	 ret |= ((intptr_t)check_zlibVersion) & 0xFFFF;
    6	return ret; }
END ./ffconf.o2M6qpqs/test.c
cl -D_ISOC99_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_USE_MATH_DEFINES -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_WIN32_WINNT=0x0600 -nologo -DHAVE_UNISTD_H=0 -MD -c -Fo./ffconf.o2M6qpqs/test.o ./ffconf.o2M6qpqs/test.c
test.c
d:\develop\visualstudio\vcpkg\installed\x86-windows\include\zconf.h(477): fatal error C1083: Cannot open include file: 'unistd.h': No such file or directory

I found that problem is in this command option -DHAVE_UNISTD_H=0.
zlib checks for this definition present and not for its value.

[velorom]

OK. In addition to the above. From the official documentation of FFmpeg:

If you wish to build with zlib support, you will have to grab a compatible zlib binary from somewhere, with an MSVC import lib, or if you wish to link statically, you can follow the instructions below to build a compatible zlib.lib with MSVC. Regardless of which method you use, you must still follow step 3, or compilation will fail.

1. Grab the zlib sources.
2. Edit win32/Makefile.msc so that it uses -MT instead of -MD, since this is how FFmpeg is built as well.
3. Edit zconf.h and remove its inclusion of unistd.h. This gets erroneously included when building FFmpeg.

[velorom]

Another addition. It looks that FFmpeg is searching for zlib.lib library name for debug version (not zlibd.lib)

[zeFresk]

Same problem using VS2019 when trying to install ffmpeg[ffmpeg,ffserver,ffplay,ffprobe,openssl,lzma,bzip2,vpx,x264,opencl,nonfree,gpl] with almost all the .lib
But the log show that release builds are fine somehow.

[LilyWangL]

@Sibras Could you please submit a Pull Request to commit your changes?
Thanks.

[Sibras]

A PR has been waiting for a while #11277