〖Android〗/system/etc/audio_policy.conf

原文件注释说明：

# 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".

其中文翻译大致如下(不太精确，勿见怪～～)：

音频设备模块部分：描述设备中包含所有音频设备模块。
每个音频设备节点有着相应的设备模块库基本名称；
例如：primary 对应着audio.primary.<devices>.so。
其中，"primary"是必须要有的，而且必须包含至少一个输出 AUDIO_OUTPUT_FLAG_PRIMARY 标志。
每个模块描述元包含一个或多个输出配置描述元和一或多个输入配置描述元。
每个配置通过给定的输出或输入流种类，列出所有支持的参数。
其中"channel_masks"、"formats"、"devices"和"flags"是由audio.h和audio_policy.h中相应的字符串指定的。
它们通过没有空格的"|"或"\n"联系起来。

其他博客的讲解：[Form: http://www.tuicool.com/articles/7J73ae]

不同的Android产品在音频的设计上通常是有差异的，利用配置文件的形式(audio_policy.conf)可以使厂商方便地描述其产品中所包含的音频设备，这个文件的存放路径有两处：

#define AUDIO_POLICY_VENDOR_CONFIG_FILE  "/vendor/etc/audio_policy.conf"

#define AUDIO_POLICY_CONFIG_FILE"/system/etc/audio_policy.conf"

联想K860手机例子：

# 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

global_configuration {
  attached_output_devices AUDIO_DEVICE_OUT_EARPIECE|AUDIO_DEVICE_OUT_SPEAKER
  default_output_device AUDIO_DEVICE_OUT_SPEAKER
  attached_input_devices AUDIO_DEVICE_IN_BUILTIN_MIC|AUDIO_DEVICE_IN_BACK_MIC
}

# 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_hw_modules {
  primary {
    outputs {
      primary {
        sampling_rates 48000
        channel_masks AUDIO_CHANNEL_OUT_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_OUT_EARPIECE|AUDIO_DEVICE_OUT_SPEAKER|AUDIO_DEVICE_OUT_WIRED_HEADSET|AUDIO_DEVICE_OUT_WIRED_HEADPHONE|AUDIO_DEVICE_OUT_ALL_SCO|AUDIO_DEVICE_OUT_LINEOUT1|AUDIO_DEVICE_OUT_LINEOUT2|AUDIO_DEVICE_OUT_FM
        flags AUDIO_OUTPUT_FLAG_PRIMARY
      }
    }
    inputs {
      primary {
        sampling_rates 8000|11025|12000|16000|22050|24000|32000|44100|48000
        channel_masks AUDIO_CHANNEL_IN_MONO|AUDIO_CHANNEL_IN_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_IN_BUILTIN_MIC|AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET|AUDIO_DEVICE_IN_WIRED_HEADSET|AUDIO_DEVICE_IN_BACK_MIC|AUDIO_DEVICE_IN_LINEIN1|AUDIO_DEVICE_IN_LINEIN2
      }
    }
  }
a2dp {
    outputs {
      a2dp {
        sampling_rates 44100
        channel_masks AUDIO_CHANNEL_OUT_STEREO
        formats AUDIO_FORMAT_PCM_16_BIT
        devices AUDIO_DEVICE_OUT_ALL_A2DP
      }
    }
  }
}