AudioTrack是不能直接来播放mp3文件的，它接收的是原始音频数据(pcm),所以必须先将mp3文件解码为pcm，然后将解码后的数据传递个AudioTrack

MediaPlayer与AudioTrack

对于Android应用开发人员来讲，音频回放最熟悉的莫过于MediaPlayer，而AudioTrack相信用的人相对会少很多。这是因为MediaPlayer提供了更完整的封装和状态控制，使得我们用很少的代码就可以实现一个简单的音乐播放器。而相比MediaPlayer，AudioTrack更为精练、高效，实际上MediaPlayerService的内部实现就是使用了AudioTrack。
AudioTrack被用于PCM音频流的回放

MediaPlayer在framework层还是会创建AudioTrack，把解码后的PCM数流传递给AudioTrack，AudioTrack再传递给AudioFlinger进行混音，然后才传递给硬件播放。
所以是MediaPlayer包含了AudioTRack
native-lib.cpp

#include <jni.h>
#include <string>
#include <android/log.h>

extern "C" {
//编码
#include "libavcodec/avcodec.h"
//封装格式处理
#include "libavformat/avformat.h"
#include "libswresample/swresample.h"
//像素处理
#include "libswscale/swscale.h"
#include <android/native_window_jni.h>
#include <unistd.h>
}
#define LOGI(FORMAT, ...) __android_log_print(ANDROID_LOG_INFO,"jason",FORMAT,##__VA_ARGS__);
#define LOGE(FORMAT, ...) __android_log_print(ANDROID_LOG_ERROR,"jason",FORMAT,##__VA_ARGS__);
extern "C"
JNIEXPORT void JNICALL
Java_com_dongnao_ffmpegmusic_DavidPlayer_sound(JNIEnv *env, jobject instance, jstring input_,
                                               jstring output_) {
    const char *input = env->GetStringUTFChars(input_, 0);
    const char *output = env->GetStringUTFChars(output_, 0);
    av_register_all();

    AVFormatContext *pFormatCtx = avformat_alloc_context();
    //第四个参数是 可以传一个 字典   是一个入参出参对象
    if (avformat_open_input(&pFormatCtx, input, NULL, NULL) != 0) {
        LOGE("%s", "打开输入视频文件失败");
    }
    //3.获取视频信息
    if (avformat_find_stream_info(pFormatCtx, NULL) < 0) {
        LOGE("%s", "获取视频信息失败");
        return;
    }


    int audio_stream_idx = -1;
    for (int i = 0; i < pFormatCtx->nb_streams; ++i) {
        if (pFormatCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
            LOGE("  找到音频id %d", pFormatCtx->streams[i]->codec->codec_type);
            audio_stream_idx = i;
            break;
        }
    }

    // 获取音频编解码器
    AVCodecContext *pCodecCtx = pFormatCtx->streams[audio_stream_idx]->codec;
    LOGE("获取视频编码器上下文 %p  ", pCodecCtx);

    AVCodec *pCodex = avcodec_find_decoder(pCodecCtx->codec_id);
    LOGE("获取视频编码 %p", pCodex);
    if (avcodec_open2(pCodecCtx, pCodex, NULL) < 0) {
    }
    //mp3音频数据
    AVPacket *packet = (AVPacket *) av_malloc(sizeof(AVPacket));
    //pcm音频数据
    AVFrame *frame;
    frame = av_frame_alloc();

    SwrContext *swrContext = swr_alloc();

    int got_frame;

    uint8_t *out_buffer = (uint8_t *) av_malloc(44100 * 2);
    /**
     * struct SwrContext *swr_alloc_set_opts(struct SwrContext *s,
          int64_t out_ch_layout, enum AVSampleFormat out_sample_fmt, int out_sample_rate,
          int64_t  in_ch_layout, enum AVSampleFormat  in_sample_fmt, int  in_sample_rate,
          int log_offset, void *log_ctx);
          7.1
     */
    uint64_t out_ch_layout = AV_CH_LAYOUT_STEREO;
    //输出采样位数  16位
    enum AVSampleFormat out_formart = AV_SAMPLE_FMT_S16;
   //输出的采样率必须与输入相同
    int out_sample_rate = pCodecCtx->sample_rate;


    swr_alloc_set_opts(swrContext, out_ch_layout, out_formart, out_sample_rate,
                       pCodecCtx->channel_layout, pCodecCtx->sample_fmt, pCodecCtx->sample_rate, 0,
                       NULL);

    swr_init(swrContext);
    //  获取通道数  2
    int out_channer_nb = av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO);
    //    反射得到Class类型
    jclass david_player = env->GetObjectClass(instance);
    //    反射得到createAudio方法
    jmethodID createAudio = env->GetMethodID(david_player, "createAudio", "(II)V");
    //    反射调用createAudio
    env->CallVoidMethod(instance, createAudio, 44100, out_channer_nb);
    jmethodID audio_write = env->GetMethodID(david_player, "playTrack", "([BI)V");
    //    输出文件
    //    FILE *pcm_file = fopen(output, "wb");
    int frameCount = 0;
    while (av_read_frame(pFormatCtx, packet) >= 0) {
        if (packet->stream_index == audio_stream_idx) {
            // 解码  mp3   编码格式frame----pcm   frame
            avcodec_decode_audio4(pCodecCtx, frame, &got_frame, packet);
            if (got_frame) {
                LOGE("解码");
                /**
                 * int swr_convert(struct SwrContext *s, uint8_t **out, int out_count,
                                const uint8_t **in , int in_count);
                 */
                swr_convert(swrContext, &out_buffer, 44100 * 2, (const uint8_t **) frame->data,
                            frame->nb_samples);
                // 缓冲区的大小
                int size = av_samples_get_buffer_size(NULL, out_channer_nb, frame->nb_samples,
                                                      AV_SAMPLE_FMT_S16, 1);
                jbyteArray audio_sample_array = env->NewByteArray(size);
                env->SetByteArrayRegion(audio_sample_array, 0, size, (const jbyte *) out_buffer);
                env->CallVoidMethod(instance, audio_write, audio_sample_array, size);
                env->DeleteLocalRef(audio_sample_array);
                // fwrite(out_buffer,1,size,pcm_file);
            }
        }
    }

    // fclose(pcm_file);
    av_frame_free(&frame);
    swr_free(&swrContext);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);


    env->ReleaseStringUTFChars(input_, input);
    env->ReleaseStringUTFChars(output_, output);
}

DavidPlayer.java

package com.dongnao.ffmpegmusic;

import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioTrack;

/**
 * Created by david on 2017/9/20.
 */

public class DavidPlayer {
    static{
        System.loadLibrary("avcodec-56");
        System.loadLibrary("avdevice-56");
        System.loadLibrary("avfilter-5");
        System.loadLibrary("avformat-56");
        System.loadLibrary("avutil-54");
        System.loadLibrary("postproc-53");
        System.loadLibrary("swresample-1");
        System.loadLibrary("swscale-3");
        System.loadLibrary("native-lib");
    }
    public native void sound(String input, String output);

    private AudioTrack audioTrack;
    /**
     * 这个方法  是C进行调用  通道数
     * @param sampleRateInHz
     * @param nb_channals
     */
    public void createAudio(int sampleRateInHz,int nb_channals) {

        int channaleConfig;
        if (nb_channals == 1) {
            channaleConfig = AudioFormat.CHANNEL_OUT_MONO;
        } else if (nb_channals == 2) {
            channaleConfig = AudioFormat.CHANNEL_OUT_STEREO;
        }else {
            channaleConfig = AudioFormat.CHANNEL_OUT_MONO;
        }
        int buffersize=AudioTrack.getMinBufferSize(sampleRateInHz,
                channaleConfig, AudioFormat.ENCODING_PCM_16BIT);

        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC,sampleRateInHz,channaleConfig,
                AudioFormat.ENCODING_PCM_16BIT,buffersize,AudioTrack.MODE_STREAM);
        audioTrack.play();
    }

    /**
     * C传入音频数据
     * @param buffer
     * @param lenth
     */
    public synchronized  void playTrack(byte[] buffer, int lenth) {
        if (audioTrack != null && audioTrack.getPlayState() == AudioTrack.PLAYSTATE_PLAYING) {
            audioTrack.write(buffer, 0, lenth);
        }
    }
}

MainActivity.java

package com.dongnao.ffmpegmusic;

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

import java.io.File;

public class MainActivity extends AppCompatActivity {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }


    public void player(View view) {
        String input = new File(Environment.getExternalStorageDirectory(),"ffmpeg.mp3").getAbsolutePath();
        String output = new File(Environment.getExternalStorageDirectory(),"ffmpeg.pcm").getAbsolutePath();
        DavidPlayer davidPlayer = new DavidPlayer();
        davidPlayer.sound(input,output);
    }
}