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-libavcodec-56avdevice-56avfilter-5avformat-56avutil-54postproc-53swresample-1swscale-3android//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;@Overrideprotected 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() {@Overridepublic void run() {playByAudio(input1.getAbsolutePath());}}.start();break;case R.id.btn_opensl:final File input2 = new File(Environment.getExternalStorageDirectory(), "input.mp3");new Thread() {@Overridepublic 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_XXXSLuint32 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 */SLresultregisterCallback(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openslSLresult 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AVFormatContextif (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 Hzswr_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 / 8out_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AVPacketif (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();
}

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