音频处理和前几篇视频处理大同小异，只不过用的转换方法不太一样（swr_convert）。

一、代码

1、java 部分;

public class MyPlayer {
    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;

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

MainActivity :

public class MainActivity extends AppCompatActivity {

    String input;
    String output;
    MyPlayer player;

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

        input = new File(Environment.getExternalStorageDirectory(), "input.mp3").getAbsolutePath();
        output = new File(Environment.getExternalStorageDirectory(), "output.pcm").getAbsolutePath();
        player = new MyPlayer();

    }

    public void play(View view) {

        player.sound(input, output);
    }

}

2、c代码：

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

extern "C" {
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswresample/swresample.h"
#include "libswscale/swscale.h"
#include <android/native_window_jni.h>
#include <unistd.h>
}
#define LOGE(FORMAT, ...) __android_log_print(ANDROID_LOG_ERROR,"keke",FORMAT,##__VA_ARGS__);
extern "C"
JNIEXPORT void

JNICALL
Java_com_example_ffmpegaudio_MyPlayer_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 *pFormatContext = avformat_alloc_context();
    if (avformat_open_input(&pFormatContext, input, NULL, NULL) != 0) {
        LOGE("打开输入文件失败");
    }

    if (avformat_find_stream_info(pFormatContext, NULL) < 0) {
        LOGE("获取信息失败");
    }

    int audio_stream_index = -1;

    for (int i = 0; i < pFormatContext->nb_streams; ++i) {
        if (pFormatContext->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
            audio_stream_index = i;
            break;
        }
    }

    AVCodecContext *pCodecCtx = pFormatContext->streams[audio_stream_index]->codec;

    AVCodec *pCodec = avcodec_find_decoder(pCodecCtx->codec_id);

    if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0) {

    }

    AVPacket *packet = (AVPacket *) av_malloc(sizeof(AVPacket));

    AVFrame *frame;
    frame = av_frame_alloc();

    SwrContext *swrContext = swr_alloc();

    int got_frame;

    uint8_t *out_buffer = (uint8_t *) av_malloc(44100 * 2);

    uint64_t out_ch_layout = AV_CH_LAYOUT_STEREO;

    enum AVSampleFormat out_format = AV_SAMPLE_FMT_S16;

    int out_sample_rate = pCodecCtx->sample_rate;

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

    swr_init(swrContext);


    int out_channals_nb = av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO);
    jclass my_player = env->GetObjectClass(instance);

    jmethodID createAudio = env->GetMethodID(my_player, "createAudio", "(II)V");

    env->CallVoidMethod(instance,createAudio,44100,out_channals_nb);

    jmethodID playTrack = env->GetMethodID(my_player, "playTrack", "([BI)V");


    while (av_read_frame(pFormatContext, packet)>=0) {
        if (packet->stream_index == audio_stream_index) {

            avcodec_decode_audio4(pCodecCtx,frame,&got_frame,packet);

            if (got_frame) {
                LOGE("解码");

                swr_convert(swrContext, &out_buffer, 44100 * 2, (const uint8_t **) frame->data, frame->nb_samples);

                int size = av_samples_get_buffer_size(NULL, out_channals_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,playTrack,audio_sample_array,size);
                env->DeleteLocalRef(audio_sample_array);

            }
        }

    }

    av_frame_free(&frame);
    swr_free(&swrContext);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatContext);

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

}