Problems encountered by Android Studio in the Mp3Encoder in the Advanced Guide to Audio and Video Development

Increase the problems encountered in calling Native code in java in C++

Main error:

In the directory of the corresponding class file, execute the following command to generate the JNI interface file

javah -jni com.phuket.tour.studio.Mp3Encoder

Javah has been abolished in the higher version of java, and it can be replaced by javac at present, using the following code to achieve

javac -h 保存的位置 ./Mp3Encoder.java
// ./Mp3Encoder.java是指在当前文件夹内的Mp3Encoder.java，如果不在当前文件夹内自行添加前面的文件名称

Execute the ndk-build command to compile the dynamic so library.
The problem here is huge. There are mainly 3 errors, which are all listed below. Starting from point 7, I have been looking for information for a long time to solve it.

My flow chart for each step:

First you need to install the packages you want to use

ndk, there are a lot of information on the Internet, you can find it yourself
Android API
Android SDK PT 和 B U
cmake

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1. Create a new project

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2. The first and second steps in the book are to create a Java file and write a local method.

#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG, __VA_ARGS__)
        Java_com_phuket_tour_mp3encoder_MpeEncoder_encode(JNIEnv * env, jobject obj) {
    
    
    LOGI("encoder encode");
}

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3. Create the jni folder

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If there is no such option, create a file called jni directly in main, and tell build.gradle that this is in Android.

4. Generate JNI interface file

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5. Create a cpp file in the cpp folder

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6. Create the Android.mk file

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_SRC_FILES = ./Mp3Encoder.cpp
LOCAL_LDLIBS :=-L$(SYSROOT)/usr/lib -llog
LOCAL_MODULE := jni
include $(BUILD_SHARED_LIBRARY)

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An error will be reported later, and I will tell you one by one how to correct the error. First, let’s see what error is reported:

7. Three Questions

Android NDK: APP_PLATFORM not set. Defaulting to minimum supported version android-16

Solution:
This requires us to set up an Application.mk and set APP_PLATFORM

APP_STL := c++_static
APP_CPPFLAGS := -frtti -fexceptions -std=c++0x
APP_ABI := armeabi-v7a
APP_PLATFORM := android-16

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This error will not be reported after running ndk-build once.

Android NDK: WARNING: APP_PLATFORM android-16 is higher than android:minSdkVersion 1 in D:/Android_app/mp3encoder2/app/src/main/AndroidManifest.xml. NDK binaries will not be compatible with devices older than android-16.

Solution:
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This solves it, run it once
Source of the second solution: https://blog.csdn.net/jiao_mrswang/article/details/79820228

make: *** No rule to make target ‘D:/Android_app/mp3encoder2/app/src/main/jni/./Mp3Encoder.cpp’, needed by ‘D:/Android_app/mp3encoder2/app/src/main/obj/local/armeabi-v7a/objs/jni/./Mp3
Encoder.o’. Stop.

This problem is caused by the LOCAL_SRC_FILES = ./Mp3Encoder.cpp in this Android.mk
No rule to make target: the translation means that there is no rule to create a target, that is, this LOCAL_SRC_FILES is wrong. See the error and know it, Mp3Encoder. The address of cpp is wrong. In fact, it is in cpp, not in jni. I still don't know how to correct the error by modifying the value. I can only determine the target file of Android.mk by other methods:
first delete LOCAL_SRC_FILES = ./Mp3Encoder.cpp, and then as shown below:
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Then run: