[FFmpeg-user] ffmpeg cross compile error

[Moritz Barsnick]

On Wed, Jul 24, 2019 at 15:28:04 +0200, Thomas Schmiedl wrote:
> Hello,
>
> I try to cross compile ffmpeg (git) using this toolchain
> https://freetz.github.io/ for a MIPS-based router. My goal is to extract
> a single image from this mjpeg-webcam-stream
> http://gwm.ccshpraha.cz:8087/. Attached are the make output and
> config.log (contains the configure parameters)
[...]
> CC	libavdevice/alldevices.o
> In file included from /home/user/freetz/toolchain/build/mips_gcc-5.5.0_uClibc-1.0.14-nptl_kernel-3.10/mips-linux-uclibc/include/stdlib.h:32:0,
>                  from /home/user/freetz/toolchain/build/mips_gcc-5.5.0_uClibc-1.0.14-nptl_kernel-3.10/mips-linux-uclibc/include/bits/sched.h:116,
>                  from /home/user/freetz/toolchain/build/mips_gcc-5.5.0_uClibc-1.0.14-nptl_kernel-3.10/mips-linux-uclibc/include/sched.h:34,
>                  from /home/user/freetz/toolchain/build/mips_gcc-5.5.0_uClibc-1.0.14-nptl_kernel-3.10/mips-linux-uclibc/include/pthread.h:24,
>                  from ./libavutil/thread.h:30,
>                  from libavdevice/alldevices.c:22:
> ./config.h:17:19: error: expected identifier or '(' before 'void'
>  #define getenv(x) NULL
>                    ^
> ./config.h:17:19: error: expected ')' before numeric constant
>  #define getenv(x) NULL
>                    ^
> In file included from ./libavutil/internal.h:176:0,
>                  from ./libavutil/common.h:491,
>                  from ./libavutil/avutil.h:296,
>                  from ./libavutil/samplefmt.h:24,
>                  from ./libavcodec/avcodec.h:31,
>                  from ./libavformat/avformat.h:317,
>                  from ./libavformat/internal.h:27,
>                  from libavdevice/alldevices.c:23:
> ./libavutil/libm.h:54:32: error: static declaration of 'cbrt' follows non-static declaration
>  static av_always_inline double cbrt(double x)
>                                 ^

This looks like this:
https://github.com/openwrt/packages/issues/6735

and the workaround seems to be adding "--cpu=<something>". See
https://github.com/openwrt/packages/pull/6743/commits/8067051bfc99f48d02aec52265fc9b78f8e60dee

I don't know if there's a real bug in ffmpeg's source here. This here:

> ./config.h:17:19: error: expected identifier or '(' before 'void'
>  #define getenv(x) NULL

indicates that the NULL macro is different on MIPS, and ffmpeg's macro
might have to be:

>  #define getenv(x) (NULL)

just in case??

Moritz