audio_policy.conf说明（翻译）

#
# Audio policy configuration for generic device builds (goldfish audio HAL - emulator)
#这是模拟器的Audio policy配置
#

# Global configuration section: lists input and output devices always present on the device
# as well as the output device selected by default.
# Devices are designated by a string that corresponds to the enum in audio.h

#全局配置部分：列出了设备上总是存在的输入输出设备，它也是系统默认选择的输出设备
#这里的输入输出设备必须是audio.h中列出的枚举类型

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_DEVICE_IN_REMOTE_SUBMIX
}

# audio hardware module section: contains descriptors for all audio hw modules present on the
# device. Each hw module node is named after the corresponding hw module library base name.
# For instance, "primary" corresponds to audio.primary.<device>.so.
# The "primary" module is mandatory and must include at least one output with
# AUDIO_OUTPUT_FLAG_PRIMARY flag.
# Each module descriptor contains one or more output profile descriptors and zero or more
# input profile descriptors. Each profile lists all the parameters supported by a given output
# or input stream category.
# The "channel_masks", "formats", "devices" and "flags" are specified using strings corresponding
# to enums in audio.h and audio_policy.h. They are concatenated by use of "|" without space or "\n".

#audio hardware module部分：包含了对设备上的所有的audio hw modules的descriptors，每一个hw module节点
#的名字都与相应的so库名称相对应，例如："primary"对应audio.primary.<device>.so。其中"primary"module是
#必须的，而且它必须包含一个含AUDIO_OUTPUT_FLAG_PRIMARY标志的output，每一个module的descriptor必须至少
#包含一个output配置descriptor和大于等于0个的input配置descriptor，每一个配置都描述了输入输出流类型支持
#的参数，其中的 "channel_masks"、"formats"、"devices"和"flags"必须为audio.h、audio_policy.h中定义的枚
#举值，它们可以通过|连接，但不能包含空格和"\n"。
audio_hw_modules {
  primary {
    outputs {
      primary {
        sampling_rates 44100
        channel_masks AUDIO_CHANNEL_OUT_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_OUT_SPEAKER
        flags AUDIO_OUTPUT_FLAG_PRIMARY
      }
    }
    inputs {
      primary {
        sampling_rates 8000|16000
        channel_masks AUDIO_CHANNEL_IN_MONO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_IN_BUILTIN_MIC
      }
    }
  }
  r_submix {
    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
      }
    }
  }
}