Simplify Flac extension build process

Removed `Android.mk` and `Application.mk`, allowing `CMake` to run directly from the build.gradle file. Users no longer need to check out `NDK` or depend on it, simplifying the usage of the Flac extension.

Also fixed a copy-pasted comment in `CMakeLists.txt` of Opus and IAMF.

PiperOrigin-RevId: 684769561

libraries/decoder_flac/README.md

@@ -17,7 +17,7 @@ To use the module you need to clone this GitHub project and depend on its
 modules locally. Instructions for doing this can be found in the
 [top level README][].
 
-In addition, it's necessary to build the module's native components as follows:
+In addition, it's necessary to fetch libflac as follows:
 
 * Set the following environment variables:
 
@@ -26,30 +26,24 @@ cd "<path to project checkout>"
 FLAC_MODULE_PATH="$(pwd)/libraries/decoder_flac/src/main"
 ```
 
-* Download the [Android NDK][] and set its location in an environment variable.
-  This build configuration has been tested on NDK r21.
-
-```
-NDK_PATH="<path to Android NDK>"
-```
-
-* Download and extract flac-1.3.2 as "${FLAC_MODULE_PATH}/jni/flac" folder:
+* Fetch libflac:
 
 ```
 cd "${FLAC_MODULE_PATH}/jni" && \
-curl https://ftp.osuosl.org/pub/xiph/releases/flac/flac-1.3.2.tar.xz | tar xJ && \
-mv flac-1.3.2 flac
+git clone https://github.com/xiph/flac.git libflac
 ```
 
-* Build the JNI native libraries from the command line:
+* [Install CMake][]
 
-```
-cd "${FLAC_MODULE_PATH}"/jni && \
-${NDK_PATH}/ndk-build APP_ABI=all -j4
-```
+Having followed these steps, gradle will build the module automatically when run
+on the command line or via Android Studio, using [CMake][] and [Ninja][] to
+configure and build libflac and the module's [JNI wrapper library][].
 
 [top level README]: ../../README.md
-[Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html
+[Install CMake]: https://developer.android.com/studio/projects/install-ndk
+[CMake]: https://cmake.org/
+[Ninja]: https://ninja-build.org
+[JNI wrapper library]: src/main/jni/flac_jni.cc
 
 ## Build instructions (Windows)
 

libraries/decoder_flac/build.gradle

@@ -17,13 +17,19 @@ android {
     namespace 'androidx.media3.decoder.flac'
 
     sourceSets {
-        main {
-            jniLibs.srcDir 'src/main/libs'
-            jni.srcDirs = [] // Disable the automatic ndk-build call by Android Studio.
-        }
         androidTest.assets.srcDir '../test_data/src/test/assets'
     }
 
+    defaultConfig {
+        externalNativeBuild {
+            cmake {
+                arguments "-DWITH_OGG=OFF"
+                arguments "-DINSTALL_MANPAGES=OFF"
+                targets "flacJNI"
+            }
+        }
+    }
+
     // TODO(Internal: b/372449691): Remove packagingOptions once AGP is updated
     // to version 8.5.1 or higher.
     packagingOptions {
@@ -33,6 +39,22 @@ android {
     }
 }
 
+// Configure the native build only if libflac is present to avoid gradle sync
+// failures if libflac hasn't been built according to the README instructions.
+if (project.file('src/main/jni/libflac').exists()) {
+    android.externalNativeBuild.cmake {
+        path = 'src/main/jni/CMakeLists.txt'
+        version = '3.21.0+'
+        if (project.hasProperty('externalNativeBuildDir')) {
+            if (!new File(externalNativeBuildDir).isAbsolute()) {
+                ext.externalNativeBuildDir =
+                        new File(rootDir, it.externalNativeBuildDir)
+            }
+            buildStagingDirectory = "${externalNativeBuildDir}/${project.name}"
+        }
+    }
+}
+
 dependencies {
     implementation project(modulePrefix + 'lib-decoder')
     // TODO(b/203752526): Remove this dependency.

libraries/decoder_flac/src/main/jni/CMakeLists.txt

@@ -0,0 +1,51 @@
+#
+# Copyright 2024 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+cmake_minimum_required(VERSION 3.21.0 FATAL_ERROR)
+
+# Enable C++11 features.
+set(CMAKE_CXX_STANDARD 11)
+
+# Define project name for your JNI module
+project(libflacJNI C CXX)
+
+set(libflac_jni_root "${CMAKE_CURRENT_SOURCE_DIR}")
+
+# Build libflac.
+add_subdirectory("${libflac_jni_root}/libflac"
+                 EXCLUDE_FROM_ALL)
+
+# Build libflacJNI.
+add_library(flacJNI
+            SHARED
+            flac_jni.cc
+            flac_parser.cc)
+
+# Add the include directory from libflac.
+include_directories("${libflac_jni_root}/libflac/include")
+
+# Locate NDK log library.
+find_library(android_log_lib log)
+
+# Link libflacJNI against used libraries.
+target_link_libraries(flacJNI
+                      PRIVATE android
+                      PRIVATE FLAC
+                      PRIVATE ${android_log_lib})
+
+# Enable 16 KB ELF alignment.
+target_link_options(flacJNI
+                    PRIVATE "-Wl,-z,max-page-size=16384")

libraries/decoder_flac/src/main/jni/include/flac_parser.h

@@ -19,15 +19,15 @@
 
 #include <stdint.h>
 
+// libFLAC parser
+#include <FLAC/stream_decoder.h>
+
 #include <array>
 #include <cstdlib>
 #include <string>
 #include <vector>
 
-// libFLAC parser
-#include "FLAC/stream_decoder.h"
-
-#include "include/data_source.h"
+#include "../include/data_source.h"
 
 typedef int status_t;
 

libraries/decoder_iamf/src/main/jni/CMakeLists.txt

@@ -39,7 +39,7 @@ add_library(iamfJNI
 # Locate NDK log library.
 find_library(android_log_lib log)
 
-# Link libgav1JNI against used libraries.
+# Link libiamfJNI against used libraries.
 target_link_libraries(iamfJNI
                       PRIVATE android
                       PRIVATE iamf

libraries/decoder_opus/src/main/jni/CMakeLists.txt

@@ -39,7 +39,7 @@ add_library(opusV2JNI
 # Locate NDK log library.
 find_library(android_log_lib log)
 
-# Link libgav1JNI against used libraries.
+# Link libopusJNI against used libraries.
 target_link_libraries(opusV2JNI
                       PRIVATE android
                       PRIVATE opus