一.认识OpenSL ES
OpenSL ES的全称是Open Sound Library For Embedded Systems,即应用于嵌入式系统的开源音频库。Android从2.3版本起就开始支持OpenSL ES标准了,并且通过NDK提供相应的API开发接口。OpenSL ES有以下特性:
- 提供c语言接口,兼容c++,需要在NDK下开发,可以更好地集成于native应用
- 运行于native层,需要自己管理资源的申请和释放,没有Dalvik虚拟机垃圾回收机制
- 支持pcm数据的采集和播放
- 支持播放的音频数据来源广泛,res、assets、sdcard、在线网络音频以及代码中定义的音频二进制数据
和Android提供的AudioRecord和AudioTrack相比,OpenSL ES提供了更高的性能,更快的速度。因为AudioRecord和AudioTrack都是Android提供的Java API,无论是采集还是播放音频,都需要将音频数据从java层拷贝到native层,或从native层拷贝到java层,这无疑是十分消耗资源的。如果希望减少拷贝,开发更加高效的Android音频应用,则建议使用Android NDK提供的OpenSL ES API接口,它支持在native层直接处理音频数据。
二.使用OpenSL ES播放pcm音频数据的步骤
开发步骤如下:
- 创建引擎对象和接口
- 创建混音器对象和接口
- 创建播放器对象和接口
- 创建缓冲队列接口并给缓冲队列注册回调函数
- 设置播放状态,手动调用回调函数
下面给出代码:
//opensles.cpp
#include<cstdint>
#include<iostream>
#include<jni.h>
extern "C"{
#include<SLES/OpenSLES.h>
#include<android/log.h>
#include<SLES/OpenSLES_Android.h>
}
#define TAG "jni" // 这个是自定义的LOG的标识
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__) // 定义LOGD类型
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO,TAG ,__VA_ARGS__) // 定义LOGI类型
#define LOGW(...) __android_log_print(ANDROID_LOG_WARN,TAG ,__VA_ARGS__) // 定义LOGW类型
#define LOGE(...) __android_log_print(ANDROID_LOG_ERROR,TAG ,__VA_ARGS__) // 定义LOGE类型
#define LOGF(...) __android_log_print(ANDROID_LOG_FATAL,TAG ,__VA_ARGS__) // 定义LOGF类型
using namespace std;
//engine interface
static SLObjectItf engineObject= nullptr;
static SLEngineItf engineEngine= nullptr;
//output mix interfaces
static SLObjectItf outputMixObject= nullptr;
static SLEnvironmentalReverbItf outputMixEnvironmentalReverb= nullptr;
//player interface
static SLObjectItf pcmPlayerObject= nullptr;
static SLPlayItf pcmPlayerplay= nullptr;
//buffer queue
static SLAndroidSimpleBufferQueueItf pcmBufferQueue= nullptr;
//pcm file
FILE *pcmFile= nullptr;
void *buffer= nullptr;
uint8_t *out_buffer= nullptr;
static const SLEnvironmentalReverbSettings reverbSettings=SL_I3DL2_ENVIRONMENT_PRESET_STONECORRIDOR;
//播放回调
void playerCallback(SLAndroidSimpleBufferQueueItf bufferQueueItf,void *context){
if(bufferQueueItf!=pcmBufferQueue){
LOGI("SLAndroidSimpleBufferQueueItf is not equal");
return;
}
while(!feof(pcmFile)){
size_t size=fread(out_buffer,44100*2*4,1,pcmFile);
if(out_buffer== nullptr||size==0){
LOGI("read end %ld",size);
}else{
LOGI("reading %ld",size);
}
buffer=out_buffer;
break;
}
if(buffer){
LOGI("buffer is not null");
SLresult result=(*pcmBufferQueue)->Enqueue(pcmBufferQueue,buffer,44100*2*4);
if(result!=SL_RESULT_SUCCESS){
LOGI("pcmBufferQueue error %ld",result);
}
}
}
jint playPcmBySL(JNIEnv *env,jobject thiz,jstring pcm_path){
const char *pcmPath=env->GetStringUTFChars(pcm_path, nullptr);
pcmFile=fopen(pcmPath,"r");
env->ReleaseStringUTFChars(pcm_path,pcmPath);
if(pcmFile== nullptr){
LOGI("open pcmFile error");
return -1;
}
out_buffer=(uint8_t *)malloc(44100*2*4);
//创建引擎对象
SLresult result=slCreateEngine(&engineObject,0,nullptr,0,nullptr,nullptr);
if(result!=SL_RESULT_SUCCESS){
LOGI("slCreateEngine failed %ld",result);
return -1;
}
//实例化引擎
result=(*engineObject)->Realize(engineObject,SL_BOOLEAN_FALSE);
if(result!=SL_RESULT_SUCCESS){
LOGI("engine realize failed %ld",result);
return -1;
}
//获取引擎接口SLEngineItf
result=(*engineObject)->GetInterface(engineObject,SL_IID_ENGINE,&engineEngine);
if(result!=SL_RESULT_SUCCESS){
LOGI("GetInterface SLEngineItf failed %ld",result);
return -1;
}
//创建输出混音器
const SLInterfaceID ids[1]={SL_IID_ENVIRONMENTALREVERB};
const SLboolean req[1]={SL_BOOLEAN_FALSE};
result=(*engineEngine)->CreateOutputMix(engineEngine,&outputMixObject,1,ids,req);
if(result!=SL_RESULT_SUCCESS){
LOGI("CreateOutputMix failed %ld",result);
return -1;
}
//实例化混音器
result=(*outputMixObject)->Realize(outputMixObject,SL_BOOLEAN_FALSE);
if(result!=SL_RESULT_SUCCESS){
LOGI("Realize outputMixObject failed %ld",result);
return -1;
}
//获取混音器接口SLEnvironmentalReverbItf
result=(*outputMixObject)->GetInterface(outputMixObject,SL_IID_ENVIRONMENTALREVERB,&outputMixEnvironmentalReverb);
if(result!=SL_RESULT_SUCCESS){
LOGI("GetInterface SLEnvironmentalReverbItf failed %ld",result);
return -1;
}
//给混音器设置环境混响属性
(*outputMixEnvironmentalReverb)->SetEnvironmentalReverbProperties(outputMixEnvironmentalReverb,&reverbSettings);
//设置输入 SLDataSource
SLDataLocator_AndroidSimpleBufferQueue loc_bufq={SL_DATALOCATOR_ANDROIDSIMPLEBUFFERQUEUE,2};
SLDataFormat_PCM formatPcm={
SL_DATAFORMAT_PCM,
2,
SL_SAMPLINGRATE_44_1,
SL_PCMSAMPLEFORMAT_FIXED_32,
SL_PCMSAMPLEFORMAT_FIXED_32,
SL_SPEAKER_FRONT_LEFT|SL_SPEAKER_FRONT_RIGHT,
SL_BYTEORDER_LITTLEENDIAN
};
SLDataSource slDataSource={&loc_bufq,&formatPcm};
//设置输出SLDataSink
SLDataLocator_OutputMix loc_outmix={SL_DATALOCATOR_OUTPUTMIX,outputMixObject};
SLDataSink audioSnk={&loc_outmix, nullptr};
//创建音频播放器对象
const SLInterfaceID ids2[1] = {SL_IID_BUFFERQUEUE};
const SLboolean req2[1] = {SL_BOOLEAN_TRUE};
result=(*engineEngine)->CreateAudioPlayer(engineEngine,&pcmPlayerObject,&slDataSource,&audioSnk,1,ids2,req2);
if(result!=SL_RESULT_SUCCESS){
LOGI("CreateAudioPlayer failed %ld",result);
return -1;
}
//实例化音频播放器对象
result=(*pcmPlayerObject)->Realize(pcmPlayerObject,SL_BOOLEAN_FALSE);
if(result!=SL_RESULT_SUCCESS){
LOGI("Realize pcmPlayerObject failed %ld",result);
return -1;
}
//获取音频播放器接口pcmPlayerplay
result=(*pcmPlayerObject)->GetInterface(pcmPlayerObject,SL_IID_PLAY,&pcmPlayerplay);
if(result!=SL_RESULT_SUCCESS){
LOGI("GetInterface pcmPlayerplay failed %ld",result);
return -1;
}
//获取音频播放的buffer接口SLAndroidSimpleBufferQueueItf
result=(*pcmPlayerObject)->GetInterface(pcmPlayerObject,SL_IID_BUFFERQUEUE,&pcmBufferQueue);
if(result!=SL_RESULT_SUCCESS){
LOGI("GetInterface pcmBufferQueue failed %ld",result);
return -1;
}
//注册回调RegisterCallback
result=(*pcmBufferQueue)->RegisterCallback(pcmBufferQueue,playerCallback, nullptr);
if(result!=SL_RESULT_SUCCESS){
LOGI("RegisterCallback failed %ld",result);
return -1;
}
//设置播放状态为playing
result=(*pcmPlayerplay)->SetPlayState(pcmPlayerplay,SL_PLAYSTATE_PLAYING);
if(result!=SL_RESULT_SUCCESS){
LOGI("SetPlayState failed %ld",result);
return -1;
}
//触发回调
playerCallback(pcmBufferQueue, nullptr);
return 0;
}
CMakeLists.txt文件:
cmake_minimum_required(VERSION 3.22.1)
project("mediaplayer")
add_library(${CMAKE_PROJECT_NAME} SHARED
# 将自己写的cpp源文件编译成动态库
opensles.cpp)
target_link_libraries(${CMAKE_PROJECT_NAME}
# List libraries link to the target library
android
log
OpenSLES
)
在java层只需获取到要播放的pcm文件的位置,然后传入native层即可,代码如下:
val pcmPath=getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS)?.absolutePath+File.separator+"input.pcm"
playPcmBySL(pcmPath)
需要注意的是,pcm文件可以通过使用ffmpeg解码mp3文件得到,但是在解码的时候需要注意的是:解码时位深别用32位浮点型,播放出来会有很大的噪音,最好用有符号的32位整型。原因尚未找到,可能是opensl es不支持32位浮点型位深吧。
可以用以下命令解码得到pcm文件:ffmpeg -i input.mp3 -acodec pcm_s32le -f s32le -ac 2 -ar 44100 -y output.pcm