Android开发学习之路--Android Studio cmake编译ffmpeg

??最新的android studio2.2引入了cmake可以很好地实现ndk的编写。

ffmpeg编译

??进入正题，既然是ffmpeg的移植编译，那么就先下载ffmpeg，https://ffmpeg.org/download.html。这里下载的是3.0.3版本。
??新建ffmpeg文件夹，然后新建脚本用来编译ffmpeg，命名为build.sh，脚本如下：

??主要是实现了四个button，分别是protocol，format，codec和filter。如下图所示：

??
??修改jni部分的代码，也就是native-lib.cpp的代码如下：

#include 
#include 

extern "C"
{
#include 
#include 
#include 

jstring
Java_com_jared_helloffmpeg_MainActivity_stringFromJNI(
        JNIEnv *env, jobject) {
    std::string hello = "Hello from C++";
    return env->NewStringUTF(hello.c_str());
}

jstring
Java_com_jared_helloffmpeg_MainActivity_urlprotocolinfo(
        JNIEnv *env, jobject) {
    char info[40000] = {0};
    av_register_all();

    struct URLProtocol *pup = NULL;

    struct URLProtocol **p_temp = &pup;
    avio_enum_protocols((void **) p_temp, 0);

    while ((*p_temp) != NULL) {
        sprintf(info, "%sInput: %s\n", info, avio_enum_protocols((void **) p_temp, 0));
    }
    pup = NULL;
    avio_enum_protocols((void **) p_temp, 1);
    while ((*p_temp) != NULL) {
        sprintf(info, "%sInput: %s\n", info, avio_enum_protocols((void **) p_temp, 1));
    }
    return env->NewStringUTF(info);
}

jstring
Java_com_jared_helloffmpeg_MainActivity_avformatinfo(
        JNIEnv *env, jobject) {
    char info[40000] = {0};

    av_register_all();

    AVInputFormat *if_temp = av_iformat_next(NULL);
    AVOutputFormat *of_temp = av_oformat_next(NULL);
    while (if_temp != NULL) {
        sprintf(info, "%sInput: %s\n", info, if_temp->name);
        if_temp = if_temp->next;
    }
    while (of_temp != NULL) {
        sprintf(info, "%sOutput: %s\n", info, of_temp->name);
        of_temp = of_temp->next;
    }
    return env->NewStringUTF(info);
}

jstring
Java_com_jared_helloffmpeg_MainActivity_avcodecinfo(
        JNIEnv *env, jobject) {
    char info[40000] = {0};

    av_register_all();

    AVCodec *c_temp = av_codec_next(NULL);

    while (c_temp != NULL) {
        if (c_temp->decode != NULL) {
            sprintf(info, "%sdecode:", info);
        } else {
            sprintf(info, "%sencode:", info);
        }
        switch (c_temp->type) {
            case AVMEDIA_TYPE_VIDEO:
                sprintf(info, "%s(video):", info);
                break;
            case AVMEDIA_TYPE_AUDIO:
                sprintf(info, "%s(audio):", info);
                break;
            default:
                sprintf(info, "%s(other):", info);
                break;
        }
        sprintf(info, "%s[%10s]\n", info, c_temp->name);
        c_temp = c_temp->next;
    }

    return env->NewStringUTF(info);
}

jstring
Java_com_jared_helloffmpeg_MainActivity_avfilterinfo(
        JNIEnv *env, jobject) {
    char info[40000] = {0};
    avfilter_register_all();

    AVFilter *f_temp = (AVFilter *)avfilter_next(NULL);
    while(f_temp != NULL) {
        sprintf(info, "%s%s\n", info, f_temp->name);
        f_temp = f_temp->next;
    }
    return env->NewStringUTF(info);
}
}

??这里要特别注意ffmpeg的头文件已经调用的代码要extern “C”里面，要不然会报错误的。

??最后就是java调用代码了。如下所示：

package com.jared.helloffmpeg;

import android.databinding.DataBindingUtil;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;

import com.jared.helloffmpeg.databinding.MainBinding;

import static java.lang.System.loadLibrary;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private MainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);
        binding = DataBindingUtil.setContentView(this, R.layout.activity_main);
        binding.btnProtocol.setOnClickListener(this);
        binding.btnCodec.setOnClickListener(this);
        binding.btnFilter.setOnClickListener(this);
        binding.btnFormat.setOnClickListener(this);
        // Example of a call to a native method
        //TextView tv = (TextView) findViewById(R.id.sample_text);
        //tv.setText(avformatinfo());
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn_protocol:
                binding.tvInfo.setText(urlprotocolinfo());
                break;
            case R.id.btn_format:
                binding.tvInfo.setText(avformatinfo());
                break;
            case R.id.btn_codec:
                binding.tvInfo.setText(avcodecinfo());
                break;
            case R.id.btn_filter:
                binding.tvInfo.setText(avfilterinfo());
                break;
            default:
                break;
        }
    }

    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();

    public native String urlprotocolinfo();
    public native String avformatinfo();
    public native String avcodecinfo();
    public native String avfilterinfo();

    // Used to load the 'native-lib' library on application startup.
    static {
        loadLibrary("native-lib");
    }
}

??都准备好了，那么就继续运行看看结果了：

??基本上Android Studio下的cmake编译ffmpeg就到此结束了，那么接下去就可以在android手机上使用ffmpeg来做一些音视频相关的东西了。