Unable to compile ffmpeg extension with NDK 23 + CMake-3.22

[goffioul]

My setup:

• ExoPlayer 2.15.1
• Android NDK 23.1.7779620
• CMake 3.22.2 (using system package from Fedora)

In order to build with this setup, I'm using the following patch:

diff --git a/extensions/ffmpeg/build.gradle b/extensions/ffmpeg/build.gradle
index a9edeaff6b..14d3bc9fbb 100644
--- a/extensions/ffmpeg/build.gradle
+++ b/extensions/ffmpeg/build.gradle
@@ -17,7 +17,8 @@ apply from: "$gradle.ext.exoplayerSettingsDir/common_library_config.gradle"
 // failures if ffmpeg hasn't been built according to the README instructions.
 if (project.file('src/main/jni/ffmpeg').exists()) {
     android.externalNativeBuild.cmake.path = 'src/main/jni/CMakeLists.txt'
-    android.externalNativeBuild.cmake.version = '3.7.1+'
+    android.externalNativeBuild.cmake.version = '3.18.0+'
+    android.ndkVersion = '23.1.7779620'
 }
 
 dependencies {
diff --git a/extensions/ffmpeg/src/main/jni/build_ffmpeg.sh b/extensions/ffmpeg/src/main/jni/build_ffmpeg.sh
index 7b2e933902..e678d2ef2e 100755
--- a/extensions/ffmpeg/src/main/jni/build_ffmpeg.sh
+++ b/extensions/ffmpeg/src/main/jni/build_ffmpeg.sh
@@ -49,10 +49,10 @@ cd "${FFMPEG_EXT_PATH}/jni/ffmpeg"
     --arch=arm \
     --cpu=armv7-a \
     --cross-prefix="${TOOLCHAIN_PREFIX}/armv7a-linux-androideabi16-" \
-    --nm="${TOOLCHAIN_PREFIX}/arm-linux-androideabi-nm" \
-    --ar="${TOOLCHAIN_PREFIX}/arm-linux-androideabi-ar" \
-    --ranlib="${TOOLCHAIN_PREFIX}/arm-linux-androideabi-ranlib" \
-    --strip="${TOOLCHAIN_PREFIX}/arm-linux-androideabi-strip" \
+    --nm="${TOOLCHAIN_PREFIX}/llvm-nm" \
+    --ar="${TOOLCHAIN_PREFIX}/llvm-ar" \
+    --ranlib="${TOOLCHAIN_PREFIX}/llvm-ranlib" \
+    --strip="${TOOLCHAIN_PREFIX}/llvm-strip" \
     --extra-cflags="-march=armv7-a -mfloat-abi=softfp" \
     --extra-ldflags="-Wl,--fix-cortex-a8" \
     ${COMMON_OPTIONS}
@@ -64,10 +64,10 @@ make clean
     --arch=aarch64 \
     --cpu=armv8-a \
     --cross-prefix="${TOOLCHAIN_PREFIX}/aarch64-linux-android21-" \
-    --nm="${TOOLCHAIN_PREFIX}/aarch64-linux-android-nm" \
-    --ar="${TOOLCHAIN_PREFIX}/aarch64-linux-android-ar" \
-    --ranlib="${TOOLCHAIN_PREFIX}/aarch64-linux-android-ranlib" \
-    --strip="${TOOLCHAIN_PREFIX}/aarch64-linux-android-strip" \
+    --nm="${TOOLCHAIN_PREFIX}/llvm-nm" \
+    --ar="${TOOLCHAIN_PREFIX}/llvm-ar" \
+    --ranlib="${TOOLCHAIN_PREFIX}/llvm-ranlib" \
+    --strip="${TOOLCHAIN_PREFIX}/llvm-strip" \
     ${COMMON_OPTIONS}
 make -j$JOBS
 make install-libs
@@ -77,10 +77,10 @@ make clean
     --arch=x86 \
     --cpu=i686 \
     --cross-prefix="${TOOLCHAIN_PREFIX}/i686-linux-android16-" \
-    --nm="${TOOLCHAIN_PREFIX}/i686-linux-android-nm" \
-    --ar="${TOOLCHAIN_PREFIX}/i686-linux-android-ar" \
-    --ranlib="${TOOLCHAIN_PREFIX}/i686-linux-android-ranlib" \
-    --strip="${TOOLCHAIN_PREFIX}/i686-linux-android-strip" \
+    --nm="${TOOLCHAIN_PREFIX}/llvm-nm" \
+    --ar="${TOOLCHAIN_PREFIX}/llvm-ar" \
+    --ranlib="${TOOLCHAIN_PREFIX}/llvm-ranlib" \
+    --strip="${TOOLCHAIN_PREFIX}/llvm-strip" \
     --disable-asm \
     ${COMMON_OPTIONS}
 make -j$JOBS
@@ -91,10 +91,10 @@ make clean
     --arch=x86_64 \
     --cpu=x86_64 \
     --cross-prefix="${TOOLCHAIN_PREFIX}/x86_64-linux-android21-" \
-    --nm="${TOOLCHAIN_PREFIX}/x86_64-linux-android-nm" \
-    --ar="${TOOLCHAIN_PREFIX}/x86_64-linux-android-ar" \
-    --ranlib="${TOOLCHAIN_PREFIX}/x86_64-linux-android-ranlib" \
-    --strip="${TOOLCHAIN_PREFIX}/x86_64-linux-android-strip" \
+    --nm="${TOOLCHAIN_PREFIX}/llvm-nm" \
+    --ar="${TOOLCHAIN_PREFIX}/llvm-ar" \
+    --ranlib="${TOOLCHAIN_PREFIX}/llvm-ranlib" \
+    --strip="${TOOLCHAIN_PREFIX}/llvm-strip" \
     --disable-asm \
     ${COMMON_OPTIONS}
 make -j$JOBS

I compile ffmpeg code according to build instructions:

cd extensions/ffmpeg/src/main/jni/
git clone git://source.ffmpeg.org/ffmpeg
(cd ffmpeg && \
    git checkout release/4.2)
./build_ffmpeg.sh \
    /path/to/ExoPlayer/extensions/ffmpeg/src/main \
    /path/to/android-sdk-linux/ndk/23.1.7779620 \
    linux-x86_64 \
    ac3 mp3

Finally I try to compile the demo app:

./gradlew :demo:assembleWithDecoderExtensionsDebug

Build fails at task :extension-ffmpeg:externalNativeBuildDebug. The output log at the failure is the following (there are actually a bunch of link errors, I just copied the first ones):

 [2/2] Linking CXX shared library /path/to/ExoPlayer/extensions/ffmpeg/buildout/intermediates/cmake/debug/obj/arm64-v8a/libffmpegJNI.so
  FAILED: /path/to/ExoPlayer/extensions/ffmpeg/buildout/intermediates/cmake/debug/obj/arm64-v8a/libffmpegJNI.so 
  : && /path/to/android-sdk-linux/ndk/23.1.7779620/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ --target=aarch64-none-linux-android21 --sysroot=/path/to/android-sdk-linux/ndk/23.1.7779620/toolchains/llvm/prebuilt/linux-x86_64/sysroot -fPIC -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security -fexceptions -frtti -stdlib=libc++ -g  -fno-limit-debug-info  -Wl,--build-id=sha1 -Wl,--no-rosegment -Wl,--fatal-warnings -Qunused-arguments -Wl,--no-undefined -shared -Wl,-soname,libffmpegJNI.so -o /path/to/ExoPlayer/extensions/ffmpeg/buildout/intermediates/cmake/debug/obj/arm64-v8a/libffmpegJNI.so CMakeFiles/ffmpegJNI.dir/ffmpeg_jni.cc.o  -landroid  /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libswresample.a  /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libavcodec.a  /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libavutil.a  /path/to/android-sdk-linux/ndk/23.1.7779620/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/21/liblog.so   -static-libstdc++ -latomic -lm && :
  ld: error: relocation R_AARCH64_ADR_PREL_PG_HI21 cannot be used against symbol ff_cos_32; recompile with -fPIC
  >>> defined in /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libavcodec.a(fft_float.o)
  >>> referenced by fft_neon.S:356 (libavcodec/aarch64/fft_neon.S:356)
  >>>               fft_neon.o:(fft32_neon) in archive /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libavcodec.a
  
  ld: error: can't create dynamic relocation R_AARCH64_ADD_ABS_LO12_NC against symbol: ff_cos_32 in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
  >>> defined in /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libavcodec.a(fft_float.o)
  >>> referenced by fft_neon.S:356 (libavcodec/aarch64/fft_neon.S:356)
  >>>               fft_neon.o:(fft32_neon) in archive /path/to/ExoPlayer/extensions/ffmpeg/src/main/jni/ffmpeg/android-libs/arm64-v8a/libavcodec.a

Previously, I was using Android NDK 21.0.6113669 and CMake 3.10.2.4988404 (installed with sdkmanager), which worked fine.

[goffioul]

After some research, I found these useful references:

• Building on AArch64 Linux with Clang complaining about not having fPIC briansmith/ring#1443
• https://chromium.googlesource.com/chromium/src.git/+/1ff8654cb2647b511cb32dae4ffea9f7929b1ed9

I added the following to extensions/ffmpeg/build.gradle and that fixed the link error:

android.defaultConfig.externalNativeBuild.cmake.cppFlags = [ '-Wl,-Bsymbolic' ]

[AquilesCanta]

Thanks for the report. We will only be fixing build_ffmpeg.sh, though. I don't think CMake is related to the failure, and we don't need to enforce a specific NDK version at gradle level.

A patch will appear below once this is pushed, when we'd appreciate you verify our fix satisfies your usecase.

[goffioul]

The change in CMake version as I made in extensions/ffmpeg/build.gradle is indeed not necessary (but the others in build_ffmpeg.sh and the additional link flag in extensions/ffmpeg/build.gradle are; the specific NDK version was just specific to my dev setup). However there are a few things to consider when using an older CMake version:

1. you'll see a series of warning about using an old CMake:
   https://android.googlesource.com/platform/ndk/+/refs/tags/ndk-r23b/build/cmake/android-legacy.toolchain.cmake#416
2. if you upgrade to a newer CMake, you'll run into this issue, which is the reason I changed the min CMake version:
   https://gitlab.kitware.com/cmake/cmake/-/issues/22021

[goffioul]

I see the commit doesn't include the linker flag change. Didn't run into link error when compiling? If not, what NDK version, ffmpeg version and ffmpeg codecs did you test with? (in my case, using NDK 23 and ffmpeg's ac3 + mp3, I get an error at link time)

[goffioul]

For the record, the link error is still present in 2.17.0 with NDK 23.

[AquilesCanta]

I'll take another look. I was on holiday.