4. Android native层直接使用AudioFlinger播放pcm

＜Android音频＞Android native层使用TrackPlayer播放pcm_王二の黄金时代的博客-CSDN博客

＜Android音频＞Android native层直接使用AudioFlinger播放pcm_王二の黄金时代的博客-CSDN博客

目录

一：概述   一个c语言demo可执行程序，直接使用AudioFlinger 播放pcm.

二：实现

环境  ubuntu22.04 编译 aosp11 源码

源码  main()

结果

一：概述

这是一个c语言demo程序，android源码环境，编译得到 bin文件，push到设备上在shell环境运行,播放pcm数据。如果是app java开发，没有系统源码，就不建议往下看了。

用于研究AudioFlinger源码，这是一个demo，在源码层面编译，直接获取AuduioFlinger服务，使用AudioFlinger的 public方法来播放一个demo.  原创，分析源码参考AudioTrack(native层)编写而来。 

二：实现

上demo:（github**暂未上传）

环境

• ubuntu22.04 编译 aosp11 源码，得到emulator 运行。 
• 编译本demo 得到  out/target/product/generic_x86_64/system/bin/AFdemo 可执行程序，push到 emulator上运行。
• 程序需要一个 48K，16bit, 双通道立体声的pcm 数据文件作为源，（可使用ffmpeg制作）

源码

main.cpp

/*
*   author:cnaok 20220630
*   aosp 11 http://aospxref.com/android-11.0.0_r21/
*   直接使用 AudioFlinger接口，播放pcm数据
*   参照源码中 AudioTrack.cpp 和AudioFlinger的交互
*/
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <media/AudioSystem.h>
#include <media/IAudioFlinger.h>
#include <binder/IPCThreadState.h>
#include <private/media/AudioTrackShared.h> // for audio_track_cblk_t
using namespace android;
// namespace android
// {// 以每20ms的数据量，读一次文件
#define WRITE_TIME_MS 20int track_demo()
{// 初始化下源数据FILE *fp_in = fopen("yk_48000_2_16.pcm", "r");if (fp_in == NULL){printf("[canok]erro to open file\n");return -1;}int chanles = 2; // static inline uint32_t audio_channel_count_from_out_mask(audio_channel_mask_t channel)int samplerate = 48000;int bits = 16;size_t mFrameSize = chanles * bits / 8; // channelCount * audio_bytes_per_sample(format);size_t mFrames = samplerate * WRITE_TIME_MS / 1000;int buf_size = mFrames * mFrameSize;void *buf = malloc(buf_size);if (buf == NULL){printf("[canok]malloc erro\n");return -1;}// get_audio_flingerconst sp<IAudioFlinger> &audioFlinger = AudioSystem::get_audio_flinger();if (audioFlinger == 0){std::cout << "err to get audio_flinger" << std::endl;}IAudioFlinger::CreateTrackInput input;IAudioFlinger::CreateTrackOutput output;input.speed = 1.0;input.attr = AUDIO_ATTRIBUTES_INITIALIZER;input.frameCount = samplerate * WRITE_TIME_MS / 1000;input.config = AUDIO_CONFIG_INITIALIZER;input.config.sample_rate = samplerate;input.config.channel_mask = AUDIO_CHANNEL_OUT_STEREO; // 0x1u // system/media/audio/include/system/audio-base.hinput.config.format = AUDIO_FORMAT_PCM_16_BIT;        // AUDIO_FORMAT_PCM | AUDIO_FORMAT_PCM_16_BIT; // system/media/audio/include/system/audio-base.h// input.config.offload_info = mOffloadInfoCopy;input.clientInfo.clientTid = -1;input.sessionId = AUDIO_SESSION_ALLOCATE;input.clientInfo.clientPid = IPCThreadState::self()->getCallingPid();input.clientInfo.clientUid = IPCThreadState::self()->getCallingPid();status_t status = NO_ERROR;// 1.1 Audioflinger 请求创建mAudioTrack (Audioflinger内部会根据请求input的配置,从AudioPolicy获取合适的输出设备，打开)sp<IAudioTrack> mAudioTrack = audioFlinger->createTrack(input,output,&status);std::cout << "status:" << status << std::endl;std::cout << "creatTrack_ output:" << std::endl<< "      flags " << output.flags << std::endl<< "      frameCount " << output.frameCount << std::endl<< "      notificationFrameCount " << output.notificationFrameCount << std::endl<< "      selectedDeviceId " << output.selectedDeviceId << std::endl<< "      sessionId " << output.sessionId << std::endl<< "      afFrameCount " << output.afFrameCount << std::endl<< "      afSampleRate " << output.afSampleRate << std::endl<< "      afLatencyMs " << output.afLatencyMs << std::endl<< "      outputId " << output.outputId << std::endl<< "      portId " << output.portId << std::endl;if (mAudioTrack == nullptr){printf("[canok]create audioTrack err\n");return -1;}// 1.2 start AudioTrackmAudioTrack->start();// 2.0 mCblkMemory 从AudioTrack获取mCblkMemory，用于后续 “共享内存” 操作对象sp<IMemory> mCblkMemory = mAudioTrack->getCblk();if (mCblkMemory == 0){printf("[canok]%s: Could not get control block", __func__);}// 2.1 mCblkvoid *iMemPointer = mCblkMemory->unsecurePointer();if (iMemPointer == NULL){printf("[canok]%s: Could not get control block pointer", __func__);status = NO_INIT;}audio_track_cblk_t *mCblk = static_cast<audio_track_cblk_t *>(iMemPointer);// 2.2 mProxy//创建一个 audio_track_cblk 的辅助操作对象，后续就通过这个对象，来往audioflinger放数据。sp<AudioTrackClientProxy> mProxy; // primary owner of the memorymProxy = new AudioTrackClientProxy(mCblk, mCblk + 1, output.frameCount, mFrameSize);// 3.0 从mProxy 获取buffer,填充buffer,释放bufferwhile (fread(buf, 1, buf_size, fp_in) > 0){int count = mFrames;uint8_t *bufsrc = (uint8_t *)buf;while (count > 0){printf("[canok]track: to obtainBuffer<<<<<<<<<[%s%d] count %d \n", __FUNCTION__, __LINE__, count);/* code */// 3.1获取一个 bufferProxy::Buffer audioBuffer;audioBuffer.mFrameCount = count;                           //希望获取的frame 数量。const struct timespec *requested = &ClientProxy::kForever; // 无限超时status = mProxy->obtainBuffer(&audioBuffer, requested, NULL); // elapsed 为Null, elaped是一个输出参数，他会告诉你这个调用阻塞了多少时间，如果不需要这个数，给null// 获取的audioBuffer ， mFrameCount中是实际获取到的帧数。std::cout << "obtainBufffer:" << std::endl<< "      status: " << status << std::endl<< "      mFrameCount: " << audioBuffer.mFrameCount << std::endl;if (status != NO_ERROR){printf("[canok][%s%d] erro to obtainBuffer :%d \n", __FUNCTION__, __LINE__, status);}// 3.2 填充这个buffersize_t toWrite = audioBuffer.mFrameCount * mFrameSize;printf("[canok]track:[%s%d] toWrite:%zu  srcPostion: %ld , srcLeaveSize: %ld \n", __FUNCTION__, __LINE__, toWrite, bufsrc - (uint8_t *)buf, buf_size - (bufsrc - (uint8_t *)buf));memcpy(audioBuffer.mRaw, bufsrc, toWrite);// 3.3 释放这个buffermProxy->releaseBuffer(&audioBuffer);count -= audioBuffer.mFrameCount;bufsrc += toWrite;}}free(buf);fclose(fp_in);return 0;
}
int main(int argc, const char *argv[])
{track_demo();return 0;
}
// }

Android.bp

cc_binary {name: "AFdemo",srcs: ["main.cpp",],shared_libs: ["libaudioclient","libaudioutils","libutils","libbinder",],header_libs: ["libmedia_headers",],include_dirs: [// "frameworks/av/media/libavextensions","frameworks/av/media/libnbaio/include_mono/",],cflags: ["-Wall","-Werror","-Wno-error=deprecated-declarations","-Wno-unused-parameter","-Wno-unused-variable",],
}

结果

可执行程序，push到设备上可以直接 shell环境运行，能播放声音。

参照AudioTrack源码