Add Android FFmpeg build

- Use Android NDK preinstalled in GHA
- Target ARMv7-A, ARMv8-A and (mostly for emulators) x86, x86_64
- Target API level 21 (Android 5+)
- Always enable NEON (requirement for API level 21)
- Collect binaries in osu.Framework.Android so they're bundled
  into the AAR/APK

.github/workflows/build-ffmpeg.yml

@@ -126,6 +126,32 @@ jobs:
           name: linux-x64
           path: linux-x64
 
+  build-android:
+    name: Build Android
+    runs-on: ubuntu-22.04
+    strategy:
+      matrix:
+        arch:
+          - armeabi-v7a
+          - arm64-v8a
+          - x86
+          - x86_64
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Build
+        run: osu.Framework.NativeLibs/scripts/ffmpeg/build-android.sh
+        env:
+          arch: ${{ matrix.arch }}
+
+      - name: Upload
+        uses: actions/upload-artifact@v4
+        with:
+          name: android-${{ matrix.arch }}
+          path: android-${{ matrix.arch }}
+
   make-pr:
     name: Create pull request
     runs-on: ubuntu-22.04
@@ -134,6 +160,7 @@ jobs:
       - build-win
       - build-win-arm64
       - build-linux
+      - build-android
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -158,6 +185,22 @@ jobs:
         with:
           name: win-x86
           path: osu.Framework.NativeLibs/runtimes/win-x86/native
+      - uses: actions/download-artifact@v4
+        with:
+          name: android-armeabi-v7a
+          path: osu.Framework.Android/armeabi-v7a
+      - uses: actions/download-artifact@v4
+        with:
+          name: android-arm64-v8a
+          path: osu.Framework.Android/arm64-v8a
+      - uses: actions/download-artifact@v4
+        with:
+          name: android-x86
+          path: osu.Framework.Android/x86
+      - uses: actions/download-artifact@v4
+        with:
+          name: android-x86_64
+          path: osu.Framework.Android/x86_64
 
       - uses: peter-evans/create-pull-request@v6
         with:

osu.Framework.NativeLibs/scripts/ffmpeg/build-android.sh

@@ -0,0 +1,96 @@
+#!/bin/bash
+set -eu
+
+# Android ABI level to target. 21 is the minimum supported by the NDK
+# See https://apilevels.com for info on what the API level means
+API_LEVEL="21"
+
+if [ -z "${ANDROID_NDK_ROOT:-}" ]; then
+  echo "ANDROID_NDK_ROOT must be set"
+  exit 1
+fi
+
+pushd "$(dirname "$0")" > /dev/null
+SCRIPT_PATH=$(pwd)
+popd > /dev/null
+source "$SCRIPT_PATH/common.sh"
+
+if [ -z "${arch-}" ]; then
+    PS3='Build for which arch? '
+    select arch in "armeabi-v7a" "arm64-v8a" "x86" "x86_64"; do
+        if [ -z "$arch" ]; then
+            echo "invalid option"
+        else
+            break
+        fi
+    done
+fi
+
+cpu=''
+cross_arch=''
+cc=''
+cflags=''
+asm_options=''
+
+case $arch in
+    armeabi-v7a)
+        cpu='armv7-a'
+        cross_arch='armv7-a'
+        cc="armv7a-linux-androideabi${API_LEVEL}-clang"
+        cflags='-mfpu=neon -mfloat-abi=softfp'
+        asm_options='--enable-neon --enable-asm --enable-inline-asm'
+        ;;
+
+    arm64-v8a)
+        cpu='armv8-a'
+        cross_arch='aarch64'
+        cc="aarch64-linux-android${API_LEVEL}-clang"
+        asm_options='--enable-neon --enable-asm --enable-inline-asm'
+        ;;
+
+    x86)
+        cpu='i686'
+        cross_arch='i686'
+        cc="i686-linux-android${API_LEVEL}-clang"
+        # ASM has text relocations
+        asm_options='--disable-asm'
+        ;;
+
+    x86_64)
+        cpu='x86-64'
+        cross_arch='x86_64'
+        cc="x86_64-linux-android${API_LEVEL}-clang"
+        asm_options='--enable-asm --enable-inline-asm'
+        ;;
+esac
+
+toolchain_path="$ANDROID_NDK_ROOT/toolchains/llvm/prebuilt/linux-x86_64"
+bin_path="$toolchain_path/bin"
+
+FFMPEG_FLAGS+=(
+    --enable-jni
+
+    --enable-cross-compile
+    --target-os=android
+    --cpu=$cpu
+    --arch=$cross_arch
+    --sysroot="$toolchain_path/sysroot"
+    --cc="$bin_path/$cc"
+    --cxx="$bin_path/$cc++"
+    --ld="$bin_path/$cc"
+    --ar="$bin_path/llvm-ar"
+    --as="$bin_path/$cc"
+    --nm="$bin_path/llvm-nm"
+    --ranlib="$bin_path/llvm-ranlib"
+    --strip="$bin_path/llvm-strip"
+    --x86asmexe="$bin_path/yasm"
+    --extra-cflags="-fstrict-aliasing -fPIC -DANDROID -D__ANDROID__ $cflags"
+
+    $asm_options
+)
+
+pushd . > /dev/null
+prep_ffmpeg "android-$arch"
+build_ffmpeg
+popd > /dev/null
+