Failed to build on my Apple M3. Since I am a noob....

[IntelSgt]

ChatGPT:

The root cause of the failure is in the libjxl component’s C++ build: its APNG decoder (apng.cc) is picking up the system (Mono-framework) png.h instead of the static libpng you just built, and the API signatures have changed, so you get “no matching function” errors.

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What went wrong
1. CXXFLAGS isn’t set
Your script exports

CFLAGS="-I$HOME/ffmpeg-build/workspace/include …"
CXXFLAGS=""

so C compilations see your workspace include tree (and pick up your libpng 1.6 headers), but C++ compilations do not — they fall back to /Library/Frameworks/Mono.framework/Headers/png.h (and friends), where the signatures for

png_set_keep_unknown_chunks(png_structp, int, png_bytep, int)
png_get_iCCP(png_const_structp, png_const_infop, png_charpp, …)

no longer match what apng.cc is calling.

2.	API mismatch

Even if you had the right headers, the libjxl version you’re building expects an older libpng API. In particular it wants to pass a const unsigned char* to a function that now takes a mutable png_bytep, and it passes an unsigned char** where libpng wants a char**.

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Two ways to fix it

1. Make your workspace headers visible to C++

Before building libjxl, export your include directory into CXXFLAGS (so that -I…/workspace/include comes first):

export CXXFLAGS="-I$HOME/ffmpeg-build/workspace/include"

(you can also carry over whatever flags you need, e.g. -Wno-int-conversion)

cd ffmpeg-build/packages/libjxl-0.11.1
./deps.sh
cmake
-DBUILD_SHARED_LIBS=OFF
-DCMAKE_C_FLAGS="$CFLAGS"
-DCMAKE_CXX_FLAGS="$CXXFLAGS"
-DCMAKE_INSTALL_PREFIX="$HOME/ffmpeg-build/workspace"
-DCMAKE_INSTALL_LIBDIR=lib
-DCONFIG_RUNTIME_CPU_DETECT=0
.
make -j8
make install

If you’re driving everything from your top-level script, just insert:

export CXXFLAGS="$CFLAGS"

immediately before the libjxl cmake invocation.

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2. Patch apng.cc for the new libpng API

If for some reason you can’t change your include paths, you can locally adjust the calls in lib/extras/dec/apng.cc:

--- a/lib/extras/dec/apng.cc
+++ b/lib/extras/dec/apng.cc
@@ -578,7 +578,7 @@

• png_set_keep_unknown_chunks(png_ptr, 1, kIgnoredChunks.data(),

• png_set_keep_unknown_chunks(png_ptr, 1,

•    const_cast<png_bytep>(kIgnoredChunks.data()),
     (int)kIgnoredChunks.size());
  

@@ -1094,7 +1094,7 @@

•        png_get_iCCP(ctx.png_ptr, ctx.info_ptr, &name, &compression_type,
  

•        png_get_iCCP(ctx.png_ptr, ctx.info_ptr,
  

•            reinterpret_cast<png_charpp>(&name),
             &compression_type,
             &profile, &proflen);
  

That’ll satisfy the current signatures, but it’s really just a workaround for an upstream–downstream mismatch.

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Summary
• Why it failed: C++ compile saw the wrong (Mono) png.h -> API signature mismatches in apng.cc.
• Best fix: Export your workspace include into CXXFLAGS (e.g. export CXXFLAGS="$CFLAGS") so libjxl builds against the correct libpng headers.
• Alternative: Patch the libjxl source to cast away const and match the new libpng prototypes.