[FFmpeg-devel] [PATCH] configure: improve logic and checks for nvenc

[Timo Rothenpieler]

>> +        echo 'NV_ENCODE_API_FUNCTION_LIST flist;'
>> +        echo 'void f(void) { struct { const GUID guid; } s[] = { { NV_ENC_PRESET_HQ_GUID } }; }'
> 
> This will most likely prevent nvenc from being enabled for msvc 2012, but not old
> mingw32, which is failing with the error:
> 
> src/libavcodec/nvenc.c:115:52: error: 'ENOBUFS' undeclared here (not in a function)
>      { NV_ENC_ERR_NOT_ENOUGH_BUFFER,        AVERROR(ENOBUFS), "not enough buffer"        },
> 
> I think the easiest solution would be using AVERROR_BUFFER_TOO_SMALL if ENOBUFS is
> not defined.

Yes, if that's all that's failing, I'll just do that.

> That or just disable nvenc if using mingw32 toolchains by checking "enabled
> libc_mingw32", since disabling for target-os == mingw32 would also affect mingw-w64.

> gcc-asan fails with
> 
> /usr/bin/ld: libavcodec/libavcodec.a(nvenc.o): undefined reference to symbol 'dlsym@@GLIBC_2.2.5'
> /usr/lib/../lib/libdl.so.2: error adding symbols: DSO missing from command line
> collect2: error: ld returned 1 exit status
> 
> I have no idea how to deal with this.

When and how are you seeing that error?
That usually means a wrong order of libraries/object-files on linker
command line.

>> +        echo 'int main(void) { f(); return 0; }'
>> +    } | check_cc -I$source_path
>> +    nvenc_check_res=$?
>> +
>> +    if [ $nvenc_check_res != 0 ] && enabled nvenc; then
>> +        die "NVENC enabled but test-compile failed"
>> +    fi
>> +
>> +    case $target_os in
>> +        mingw32*|mingw64*|win32|win64|linux|cygwin*)
>> +            [ $nvenc_check_res = 0 ] && enable nvenc
>> +            ;;
>> +        *)
>> +            enabled nvenc && die "NVENC is only supported on Windows and Linux"
>> +            disable nvenc
>> +            ;;
>> +    esac
>> +
>> +    unset nvenc_check_res
> 
> This test is different from other automatically detected features, and also
> unnecessarily complex.
> You should force enable nvenc earlier in the script like with other similar
> features (including hardware codecs and accelerators), then disable it on
> unsupported platforms and old/broken compilers with the corresponding checks
> and tests.
> 
> Something like this:
> [...]

Ah, so even if calling enable nvenc, --disable-nvenc on the command line
will still override it, and the "disabled nvenc" check will still work?
I wasn't aware of that, so yes, that makes it a lot simpler.

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