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 20

int 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_flinger
    const 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.h
    input.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 AudioTrack
    mAudioTrack->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 mCblk
    void *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 memory
    mProxy = new AudioTrackClientProxy(mCblk, mCblk + 1, output.frameCount, mFrameSize);

    // 3.0 从mProxy 获取buffer,填充buffer,释放buffer
    while (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 buffer
            Proxy::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buffer
            size_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buffer
            mProxy->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

4. Android native层直接使用AudioFlinger播放pcm

一：概述

二：实现

环境

源码

结果

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