NDK--利用OpenSL ES实现播放FFmpeg解码后的音频

作者: aruba | 来源:发表于2020-07-09 23:12 被阅读0次

OpenSL ES全称为Open Sound Library for Embedded Systems。OpenSL ES是无授权费、跨平台、针对嵌入式系统精心优化的硬件音频加速API。当然安卓也使用了它，AudioTrack、MediaPlayer的音频播放，底层都是利用OpenSL。和AudioTrack相同，它只接受流，不支持音频数据的编解码，所以需要结合第三方库来使用。

为什么要使用OpenSL？一般应用使用安卓SDK提供的API就足够满足使用，但对于专门音频播放的APP，系统提供的方法就有点力不从心了，比如：AudioTrack利用native层调用OpenSL，必不可免的要进行java层流数据转化为native层流数据，这就会造成一定延迟，而对于音频播放APP而言，这是不可接受的。

前面我们使用了FFmpeg解码音频流，并使用了java层的AudioTrack进行播放，今天来实现在native层直接使用OpenSL播放。

由于OpenSL系统底层本身就集成，我们只需要在CMakeLists中导入系统动态库就可以了。

target_link_libraries(
        native-lib
        avcodec-56
        avdevice-56
        avfilter-5
        avformat-56
        avutil-54
        postproc-53
        swresample-1
        swscale-3

        android
        //openSL库
        OpenSLES
        ${log-lib})

Opensl的套路如下：

1、创建引擎接口对象
2、创建混音器
3、创建播放器（录音器）
4、设置缓冲队列和回调函数
5、设置播放状态
6、启动回调函数

这边现在java中编写对应native中的方法

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;
            case R.id.btn_opensl:
                final File input2 = new File(Environment.getExternalStorageDirectory(), "input.mp3");

                new Thread() {
                    @Override
                    public void run() {
                        playByOpenSL(input2.getAbsolutePath());
                    }
                }.start();
                break;
            case R.id.btn_opensl_stop:
                stopByOpenSL();
                break;
        }

    }

    private native void playByAudio(String inputFilePath);

    private native void playByOpenSL(String inputFilePath);

    private native void stopByOpenSL();
}

在native层将opensl封装成一个类

_opensl_helper.h

//
// Created by aruba on 2020/7/6.
//

#ifndef FFMPEGAPPLICATION_OPENSL_HELPER_H
#define FFMPEGAPPLICATION_OPENSL_HELPER_H

#include <SLES/OpenSLES.h>
#include <SLES/OpenSLES_Android.h>

class OpenslHelper {
public:
    //返回结果
    SLresult result;
    //opensl引擎
    SLObjectItf engine;
    //引擎接口
    SLEngineItf engineInterface;
    //混音器
    SLObjectItf mix;
    //环境混响混音器接口
    SLEnvironmentalReverbItf environmentalReverbItf;
    //环境混响混音器环境
    const SLEnvironmentalReverbSettings settings = SL_I3DL2_ENVIRONMENT_PRESET_DEFAULT;
    //播放器
    SLObjectItf player;
    //播放接口
    SLPlayItf playInterface;
    //缓冲区
    SLAndroidSimpleBufferQueueItf bufferQueueItf;
    //音量
    SLVolumeItf volumeItf;
    //播放状态 SL_PLAYSTATE_XXX
    SLuint32 playState;

    /**
     * 创建opensl引擎接口
     * @return SLresult
     */
    SLresult createEngine();

    /**
     * 是否成功
     * @param result 
     * @return 
     */
    bool isSuccess(SLresult &result);

    /**
     * 创建混音器
     * @return SLresult
     */
    SLresult createMix();

    /**
     * 创建播放器
     * @param numChannels   声道数
     * @param samplesRate   采样率 SL_SAMPLINGRATE_XX
     * @param bitsPerSample 采样位数（量化格式） SL_PCMSAMPLEFORMAT_FIXED_XX
     * @param channelMask   立体声掩码 SL_SPEAKER_XX | SL_SPEAKER_XX
     * @return SLresult
     */
    SLresult createPlayer(int numChannels, long samplesRate, int bitsPerSample, int channelMask);

    //播放
    SLresult play();

    //暂停
    SLresult pause();

    //停止
    SLresult stop();

    /**
    * 播放器会不断调用此函数，我们需要在此回调中不断给缓冲区填充数据
    * @param bufferQueueItf 
    * @param pContext 
    */
    SLresult
    registerCallback(slAndroidSimpleBufferQueueCallback callback);

    ~OpenslHelper();
};


#endif //FFMPEGAPPLICATION_OPENSL_HELPER_H

_opensl_helper.cpp

//
// Created by aruba on 2020/7/6.
//

#include "_opensl_helper.h"

/**
 * 是否成功
 * @param result 
 * @return 
 */
bool OpenslHelper::isSuccess(SLresult &result) {
    if (result == SL_RESULT_SUCCESS) {
        return true;
    }

    return false;
}

/**
 * 创建opensl引擎接口
 * @return SLresult
 */
SLresult OpenslHelper::createEngine() {
    //创建引擎
    result = slCreateEngine(&engine, 0, NULL, 0, NULL, NULL);
    if (!isSuccess(result)) {
        return result;
    }

    //实例化引擎,第二个参数为：是否异步
    result = (*engine)->Realize(engine, SL_BOOLEAN_FALSE);
    if (!isSuccess(result)) {
        return result;
    }

    //获取引擎接口
    result = (*engine)->GetInterface(engine, SL_IID_ENGINE, &engineInterface);
    if (!isSuccess(result)) {
        return result;
    }

    return result;
}

/**
 * 创建混音器
 * @return SLresult
 */
SLresult OpenslHelper::createMix() {
    //获取混音器
    result = (*engineInterface)->CreateOutputMix(engineInterface, &mix, 0,
                                                 0, 0);
    if (!isSuccess(result)) {
        return result;
    }

    //实例化混音器
    result = (*mix)->Realize(mix, SL_BOOLEAN_FALSE);
    if (!isSuccess(result)) {
        return result;
    }

    //获取环境混响混音器接口
    SLresult environmentalResult = (*mix)->GetInterface(mix, SL_IID_ENVIRONMENTALREVERB,
                                                        &environmentalReverbItf);
    if (isSuccess(environmentalResult)) {
        //给混音器设置环境
        (*environmentalReverbItf)->SetEnvironmentalReverbProperties(environmentalReverbItf,
                                                                    &settings);
    }

    return result;
}

/**
 * 创建播放器
 * @param numChannels   声道数
 * @param samplesRate   采样率 SL_SAMPLINGRATE_XX
 * @param bitsPerSample 采样位数（量化格式） SL_PCMSAMPLEFORMAT_FIXED_XX
 * @param channelMask   立体声掩码 SL_SPEAKER_XX | SL_SPEAKER_XX
 * @return SLresult
 */
SLresult OpenslHelper::createPlayer(int numChannels, long samplesRate, int bitsPerSample,
                                    int channelMask) {
    //1.关联音频流缓冲区  设为2是防止延迟 可以在播放另一个缓冲区时填充新数据
    SLDataLocator_AndroidSimpleBufferQueue buffQueque = {SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,
                                                         2};

    //缓冲区格式
//    typedef struct SLDataFormat_PCM_ {
//        SLuint32      formatType;    //格式pcm
//        SLuint32      numChannels;   //声道数
//        SLuint32      samplesPerSec; //采样率
//        SLuint32      bitsPerSample; //采样位数（量化格式）
//        SLuint32      containerSize; //包含位数
//        SLuint32      channelMask;   //立体声
//        SLuint32      endianness;    //结束标志位
//    } SLDataFormat_PCM;
    SLDataFormat_PCM dataFormat_pcm = {SL_DATAFORMAT_PCM, numChannels, samplesRate, bitsPerSample,
                                       bitsPerSample, channelMask,
                                       SL_BYTEORDER_LITTLEENDIAN};

    //存放缓冲区地址和格式地址的结构体
//    typedef struct SLDataSource_ {
//        void *pLocator;//缓冲区
//        void *pFormat;//格式
//    } SLDataSource;
    SLDataSource audioSrc = {&buffQueque, &dataFormat_pcm};

    //2.关联混音器
//    typedef struct SLDataLocator_OutputMix {
//        SLuint32      locatorType;
//        SLObjectItf       outputMix;
//    } SLDataLocator_OutputMix;
    SLDataLocator_OutputMix dataLocator_outputMix = {SL_DATALOCATOR_OUTPUTMIX, mix};

    //混音器快捷方式 
//    typedef struct SLDataSink_ {
//        void *pLocator;
//        void *pFormat;
//    } SLDataSink;
    SLDataSink audioSnk = {&dataLocator_outputMix, NULL};

    //3.通过引擎接口创建播放器
//    SLresult (*CreateAudioPlayer) (
//            SLEngineItf self,
//            SLObjectItf * pPlayer,
//            SLDataSource *pAudioSrc,
//            SLDataSink *pAudioSnk,
//            SLuint32 numInterfaces,
//            const SLInterfaceID * pInterfaceIds,
//            const SLboolean * pInterfaceRequired
//    );
    SLInterfaceID ids[3] = {SL_IID_BUFFERQUEUE, SL_IID_EFFECTSEND, SL_IID_VOLUME};
    SLboolean required[3] = {SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE, SL_BOOLEAN_TRUE};
    result = (*engineInterface)->CreateAudioPlayer(engineInterface, &player, &audioSrc, &audioSnk,
                                                   3, ids,
                                                   required);
    if (!isSuccess(result)) {
        return result;
    }

    //播放器实例化
    result = (*player)->Realize(player, SL_BOOLEAN_FALSE);
    if (!isSuccess(result)) {
        return result;
    }

    //获取播放接口
    result = (*player)->GetInterface(player, SL_IID_PLAY, &playInterface);
    if (!isSuccess(result)) {
        return result;
    }

    result = (*player)->GetInterface(player, SL_IID_VOLUME, &volumeItf);
    if (!isSuccess(result)) {
        return result;
    }

    //注册缓冲区
    result = (*player)->GetInterface(player, SL_IID_BUFFERQUEUE, &bufferQueueItf);
    if (!isSuccess(result)) {
        return result;
    }

    return result;
}

/**
 * 设置回调接口
 * @return SLresult
 */
SLresult OpenslHelper::registerCallback(slAndroidSimpleBufferQueueCallback callback) {
    //设置回调接口
    result = (*bufferQueueItf)->RegisterCallback(bufferQueueItf, callback, NULL);
    return result;
}

//播放
SLresult OpenslHelper::play() {
    playState = SL_PLAYSTATE_PLAYING;
    result = (*playInterface)->SetPlayState(playInterface, SL_PLAYSTATE_PLAYING);

    return result;
}

//暂停
SLresult OpenslHelper::pause() {
    playState = SL_PLAYSTATE_PAUSED;
    result = (*playInterface)->SetPlayState(playInterface, SL_PLAYSTATE_PAUSED);

    return result;
}

//停止
SLresult OpenslHelper::stop() {
    playState = SL_PLAYSTATE_STOPPED;
    result = (*playInterface)->SetPlayState(playInterface, SL_PLAYSTATE_STOPPED);

    return result;
}

//析构
OpenslHelper::~OpenslHelper() {
    //播放器
    if (player != NULL) {
        (*player)->Destroy(player);
        player = NULL;
        //播放接口
        playInterface = NULL;
        //缓冲区
        bufferQueueItf = NULL;
        //音量
        volumeItf = NULL;
    }

    //混音器
    if (mix != NULL) {
        (*mix)->Destroy(mix);
        mix = NULL;
        //环境混响混音器接口
        environmentalReverbItf = NULL;
    }

    //opensl引擎
    if (engine != NULL) {
        (*engine)->Destroy(engine);
        engine = NULL;
        //引擎接口
        engineInterface = NULL;
    }

    result = NULL;
}

运用我们之前的ffmpeg代码，调用opensl进行播放

#include <jni.h>
#include <string>
#include <android/log.h>
#include <android/native_window_jni.h>
#include <unistd.h>
#include <pthread.h>
#include <stdio.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 "_opensl_helper.h"
}

OpenslHelper helper;
uint8_t *out;
int buff_size;
//char *filePath;
AVFormatContext *formatContext;
AVCodecContext *codecContext;
int audio_stream_idx;
AVPacket *pkt;
AVFrame *picture;
SwrContext *swrContext;
int channel_count;
int out_size;

void playerCallback(SLAndroidSimpleBufferQueueItf bq, void *pContext);

/**
 * 音频解码PCM，OpenSL播放
 */
extern "C"
JNIEXPORT void JNICALL
Java_com_aruba_ffmpegapplication_PcmPlayActivity_playByOpenSL(JNIEnv *env, jobject instance,
                                                              jstring inputFilePath_) {
    //初始化opensl
    SLresult result = helper.createEngine();
    if (!helper.isSuccess(result)) {
        LOGE("createEngine失败");
        return;
    }
    result = helper.createMix();
    if (!helper.isSuccess(result)) {
        LOGE("createMix失败");
        return;
    }

    const char *inputFilePath = env->GetStringUTFChars(inputFilePath_, 0);
//    const int size = sizeof(inputFilePath);
//    filePath = static_cast<char *>(malloc(size));
//    memcpy(filePath, inputFilePath, size);

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

    //打开文件
    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
    codecContext = NULL;
    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
    pkt = (AVPacket *) (av_malloc(sizeof(AVPacket)));
    av_init_packet(pkt);

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

    //音频转码组件上下文
    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
    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
    out_size = 44100 * 16 / 8;
    out = (uint8_t *) (av_malloc(out_size));

    //开始播放
    result = helper.createPlayer(2, SL_SAMPLINGRATE_44_1, SL_PCMSAMPLEFORMAT_FIXED_16,
                                 SL_SPEAKER_FRONT_LEFT | SL_SPEAKER_FRONT_RIGHT);
    if (!helper.isSuccess(result)) {
        LOGE("createPlayer失败");
        //释放资源
        av_free(out);
        out = NULL;
        swr_free(&swrContext);
        av_frame_free(&picture);
        avcodec_close(codecContext);
        avformat_free_context(formatContext);
        env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);

        return;
    }

    helper.registerCallback(playerCallback);
    helper.play();
    playerCallback(helper.bufferQueueItf, NULL);

    env->ReleaseStringUTFChars(inputFilePath_, inputFilePath);
}

void release() {
    //释放资源
    av_free_packet(pkt);
    av_freep(out);
    out = NULL;
    swr_free(&swrContext);
    av_frame_free(&picture);
    avcodec_close(codecContext);
    avformat_free_context(formatContext);
}

void getData(uint8_t **out, int *buff_size) {
    if (out == NULL || buff_size == NULL) {
        return;
    }
    int picture_ptr = 0;

    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
                *buff_size = av_samples_get_buffer_size(NULL, channel_count, picture->nb_samples,
                                                        AV_SAMPLE_FMT_S16, 1);
                break;
            }
        }
    }

    av_free_packet(pkt);
}

/**
   * 播放器会不断调用此函数，我们需要在此回调中不断给缓冲区填充数据
   * @param bufferQueueItf 
   * @param pContext 
   */
void playerCallback(SLAndroidSimpleBufferQueueItf bq, void *pContext) {
    if (helper.playState == SL_PLAYSTATE_PLAYING) {
        getData(&out, &buff_size);
        if (out != NULL && buff_size != 0) {
            (*bq)->Enqueue(bq, out, (SLuint32) (buff_size));
        }
    } else if(helper.playState == SL_PLAYSTATE_STOPPED){
        release();
        helper.~SLresult();
        helper = NULL;
    }
}

extern "C"
JNIEXPORT void JNICALL
Java_com_aruba_ffmpegapplication_PcmPlayActivity_stopByOpenSL(JNIEnv *env, jobject instance) {
    helper.stop();
}

NDK--利用OpenSL ES实现播放FFmpeg解码后的音频

前面我们使用了FFmpeg解码音频流，并使用了java层的AudioTrack进行播放，今天来实现在native层直接使用OpenSL播放。

由于OpenSL系统底层本身就集成，我们只需要在CMakeLists中导入系统动态库就可以了。

Opensl的套路如下：

这边现在java中编写对应native中的方法

在native层将opensl封装成一个类

运用我们之前的ffmpeg代码，调用opensl进行播放

最后不要忘了在cmake中添加刚刚的_opensl_helper类文件

经测试后，可以播放音频流了

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

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