NDK--利用AudioTrack播放FFmpeg解码后的音频流

上次已经得到PCM编码的音频流，今天来实现播放PCM音频流，使用安卓提供的AudioTrack，方法很简单，在native层调用java代码

首先在java中定义相应的方法：

package com.aruba.ffmpegapplication;

import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioTrack;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;

import androidx.appcompat.app.AppCompatActivity;

import java.io.File;

public class PcmPlayActivity extends AppCompatActivity {
    static {
        System.loadLibrary("native-lib");
    }

    private AudioTrack audioTrack;

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

    /**
     * 给native层回调
     *
     * @param sampleRateInHz
     * @param channelCount
     */
    private void create(int sampleRateInHz, int channelCount) {
        int channelConfig = AudioFormat.CHANNEL_OUT_MONO; //单声道
        if (channelCount == 2) {
            channelConfig = AudioFormat.CHANNEL_OUT_STEREO;
        }

        int buffSize = AudioTrack.getMinBufferSize(sampleRateInHz, channelConfig, AudioFormat.ENCODING_PCM_16BIT);//计算最小缓冲区

//    @Deprecated
//    public AudioTrack(int streamType, int sampleRateInHz, int channelConfig, int audioFormat, int bufferSizeInBytes, int mode) throws IllegalArgumentException {
//            throw new RuntimeException("Stub!");
//        }
        audioTrack = new AudioTrack(AudioManager.STREAM_MUSIC, sampleRateInHz, channelConfig, AudioFormat.ENCODING_PCM_16BIT, buffSize, AudioTrack.MODE_STREAM);
        audioTrack.play();
    }

    /**
     * 给native层回调
     */
    private void play(byte[] bytes, int size) {
        if (audioTrack != null && audioTrack.getPlayState() == AudioTrack.PLAYSTATE_PLAYING)
            audioTrack.write(bytes, 0, size);
    }

    public void click(View view) {
        switch (view.getId()) {
            case R.id.btn_audiotrack:
                final File input1 = new File(Environment.getExternalStorageDirectory(), "input.mp3");

                new Thread() {
                    @Override
                    public void run() {
                        playByAudio(input1.getAbsolutePath());
                    }
                }.start();
                break;
        }

    }

    private native void playByAudio(String inputFilePath);
}

在native层，将上次输出到文件改为调用java方法

#include 
#include 
#include 
#include 
#include 

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"
}

#define  LOG_TAG    "aruba"
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

extern "C"
JNIEXPORT void JNICALL
Java_com_aruba_ffmpegapplication_PcmPlayActivity_playByAudio(JNIEnv *env, jobject instance,
                                                             jstring inputFilePath_) {
    const char *inputFilePath = env->GetStringUTFChars(inputFilePath_, 0);

    //注册FFmpeg中各大组件
    av_register_all();

    //打开文件
    AVFormatContext *formatContext = avformat_alloc_context();
    if (avformat_open_input(&formatContext, inputFilePath, NULL, NULL) != 0) {
        LOGE("打开失败");
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        return;
    }

    //将文件信息填充进AVFormatContext
    if (avformat_find_stream_info(formatContext, NULL) < 0) {
        LOGE("获取文件信息失败");
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        return;
    }

    //获取视频流的编解码器上下文
    AVCodecContext *codecContext = NULL;
    int audio_stream_idx = -1;
    for (int i = 0; i < formatContext->nb_streams; ++i) {
        if (formatContext->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {//如果是音频流
            codecContext = formatContext->streams[i]->codec;
            audio_stream_idx = i;
            break;
        }
    }

    if (codecContext == NULL) {
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        return;
    }

    //根据编解码器上下文的id获取视频流解码器
    AVCodec *codec = avcodec_find_decoder(codecContext->codec_id);
    //打开解码器
    if (avcodec_open2(codecContext, codec, NULL) < 0) {
        LOGE("解码失败");
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
        return;
    }

    //开始读每一帧
    //存放压缩数据
    AVPacket *pkt = (AVPacket *) (av_malloc(sizeof(AVPacket)));
    av_init_packet(pkt);

    //存放解压数据
    AVFrame *picture = av_frame_alloc();

    int picture_ptr = 0;

    //音频转码组件上下文
    SwrContext *swrContext = swr_alloc();
    //AV_CH_LAYOUT_STEREO:双声道  AV_SAMPLE_FMT_S16:量化格式 16位 codecContext->sample_rate:采样率 Hz
    swr_alloc_set_opts(swrContext, AV_CH_LAYOUT_STEREO, AV_SAMPLE_FMT_S16,
                       codecContext->sample_rate,//输出采样率和输入采样率应相同
                       codecContext->channel_layout, codecContext->sample_fmt,
                       codecContext->sample_rate, 0, NULL
    );
    swr_init(swrContext);

    //原音频通道数
    int channel_count = av_get_channel_layout_nb_channels(codecContext->channel_layout);
    //单通道最大存放转码数据 所占字节 = 采样率*量化格式 / 8
    int out_size = 44100 * 16 / 8;
    uint8_t *out = (uint8_t *) (av_malloc(out_size));

    //调用java层create方法
    jclass jclz = env->GetObjectClass(instance);
    jmethodID create_method_id = env->GetMethodID(jclz, "create", "(II)V");
    env->CallVoidMethod(instance, create_method_id, 44100, av_get_channel_layout_nb_channels(AV_CH_LAYOUT_STEREO));
    jmethodID play_method_id = env->GetMethodID(jclz, "play", "([BI)V");

    while (av_read_frame(formatContext, pkt) == 0) {//读到每一帧的压缩数据存放在AVPacket
        if (pkt->stream_index == audio_stream_idx) {
            //解码
            avcodec_decode_audio4(codecContext, picture, &picture_ptr, pkt);

            LOGE("picture_ptr %d", picture_ptr);
            if (picture_ptr > 0) {
                //转码
                swr_convert(swrContext, &out, out_size,
                            (const uint8_t **) (picture->data), picture->nb_samples);

                //缓冲区真实大小
                int size = av_samples_get_buffer_size(NULL, channel_count, picture->nb_samples,
                                                      AV_SAMPLE_FMT_S16, 1);

                jbyteArray array = env->NewByteArray(size);
                env->SetByteArrayRegion(array, 0, size, (const jbyte *) (out));
                env->CallVoidMethod(instance, play_method_id, array, size);
                env->DeleteLocalRef(array);
            }
        }
        av_free_packet(pkt);
    }

    //释放资源
    av_freep(out);
    swr_free(&swrContext);
    av_frame_free(&picture);
    avcodec_close(codecContext);
    avformat_free_context(formatContext);
    env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
}

经过测试，已经可以播放了

项目地址：https://gitee.com/aruba/FFmpegApplication.git