解析audio_policy.conf(android_audio)

最新推荐文章于 2025-09-17 03:11:14 发布

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本文详细介绍了Android系统中音频策略配置文件`audio_policy.conf`的结构和内容，包括设备类型、采样率、通道配置等关键参数，并展示了加载配置的源码流程，涉及`ConfigParsingUtils`类的使用，对于理解Android音频系统的内部工作原理具有指导意义。

参考文章 https://blog.youkuaiyun.com/qq_33750826/article/details/82455026

/vendor/etc/audio_policy.conf 加载或者 /system/etc/audio_policy.conf

audio_hw_modules {
  primary {    //一个module对应厂家提供的一个so文件
    global_configuration {
      attached_output_devices AUDIO_DEVICE_OUT_SPEAKER
      default_output_device AUDIO_DEVICE_OUT_SPEAKER
      attached_input_devices AUDIO_DEVICE_IN_BUILTIN_MIC
      audio_hal_version 3.0
    }
    devices {
      speaker {
        type AUDIO_DEVICE_OUT_SPEAKER
        gains {
          gain_1 {
            mode AUDIO_GAIN_MODE_JOINT
            min_value_mB -8400
            max_value_mB 4000
            default_value_mB 0
            step_value_mB 100
          }
        }
      }
    }
    outputs {     //一个module里面可以有多个outputs
      primary {   //一个output里，表明参数
        sampling_rates 48000
        channel_masks AUDIO_CHANNEL_OUT_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices speaker                      //设备  喇叭
        flags AUDIO_OUTPUT_FLAG_PRIMARY      //这个代表是默认设备
      }
    }
    inputs {      //一个module里面可以有多个inputs
      primary {
        sampling_rates 8000|16000
        channel_masks AUDIO_CHANNEL_IN_MONO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_IN_BUILTIN_MIC   //设备  麦克
      }
    }
  }
  r_submix {
    global_configuration {
      attached_input_devices AUDIO_DEVICE_IN_REMOTE_SUBMIX
      audio_hal_version 2.0
    }
    outputs {
      submix {
        sampling_rates 48000
        channel_masks AUDIO_CHANNEL_OUT_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_OUT_REMOTE_SUBMIX
      }
    }
    inputs {
      submix {
        sampling_rates 48000
        channel_masks AUDIO_CHANNEL_IN_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_IN_REMOTE_SUBMIX
      }
    }
  }
}

frameworks/av/services/audiopolicy/common/managerdefinitions/src/ConfigParsingUtils.cpp

cnode节点在 system/core/include/cutils/config_utils.h

typedef struct cnode cnode;


struct cnode
{
    cnode *next;
    cnode *first_child;
    cnode *last_child;
    const char *name;
    const char *value;
};

//static
status_t ConfigParsingUtils::loadConfig(const char *path, AudioPolicyConfig &config)
{
    cnode *root;
    char *data;

    data = (char *)load_file(path, NULL);
    if (data == NULL) {
        return -ENODEV;
    }
    root = config_node("", "");
    config_load(root, data);

    HwModuleCollection hwModules;
    loadHwModules(root, hwModules, config);

    // legacy audio_policy.conf files have one global_configuration section, attached to primary.
    loadGlobalConfig(root, config, hwModules.getModuleFromName(AUDIO_HARDWARE_MODULE_ID_PRIMARY));

    config.setHwModules(hwModules);

    config_free(root);
    free(root);
    free(data);

    ALOGI("loadAudioPolicyConfig() loaded %s\n", path);

    return NO_ERROR;
}