audio_policy.conf說明（翻譯）

轉載自：http://www.cnblogs.com/albert1017/p/3940010.html

作者寫的很不錯，記錄下來供以後溫故。

#
# Audio policy configuration for generic device builds (goldfish audio HAL - emulator)
#這是模擬器的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


#全域性配置部分：列出了裝置上總是存在的輸入輸出裝置，它也是系統預設選擇的輸出裝置
#這裡的輸入輸出裝置必須是audio.h中列出的列舉型別


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：包含了對裝置上的所有的audio hw modules的descriptors，每一個hw module節點
#的名字都與相應的so庫名稱相對應，例如："primary"對應audio.primary.<device>.so。其中"primary"module是
#必須的，而且它必須包含一個含AUDIO_OUTPUT_FLAG_PRIMARY標誌的output，每一個module的descriptor必須至少
#包含一個output配置descriptor和大於等於0個的input配置descriptor，每一個配置都描述了輸入輸出流型別支援
#的引數，其中的 "channel_masks"、"formats"、"devices"和"flags"必須為audio.h、audio_policy.h中定義的枚
#舉值，它們可以通過|連線，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
      }
    }
  }
}

 另外，儲存各個audio_hw_module的結構體如下：

class HwModule {
        public:
                    HwModule(const char *name);
                    ~HwModule();


            void dump(int fd);


            const char *const mName; // base name of the audio HW module (primary, a2dp ...)
            audio_module_handle_t mHandle;
            Vector <IOProfile *> mOutputProfiles; // output profiles exposed by this module
            Vector <IOProfile *> mInputProfiles;  // input profiles exposed by this module
        };


        // the IOProfile class describes the capabilities of an output or input stream.
        // It is currently assumed that all combination of listed parameters are supported.
        // It is used by the policy manager to determine if an output or input is suitable for
        // a given use case,  open/close it accordingly and connect/disconnect audio tracks
        // to/from it.
        class IOProfile
        {
        public:
            IOProfile(HwModule *module);
            ~IOProfile();


            bool isCompatibleProfile(audio_devices_t device,
                                     uint32_t samplingRate,
                                     uint32_t format,
                                     uint32_t channelMask,
                                     audio_output_flags_t flags) const;


            void dump(int fd);


            // by convention, "0' in the first entry in mSamplingRates, mChannelMasks or mFormats
            // indicates the supported parameters should be read from the output stream
            // after it is opened for the first time
            Vector <uint32_t> mSamplingRates; // supported sampling rates
            Vector <audio_channel_mask_t> mChannelMasks; // supported channel masks
            Vector <audio_format_t> mFormats; // supported audio formats
            audio_devices_t mSupportedDevices; // supported devices (devices this output can be
                                               // routed to)
            audio_output_flags_t mFlags; // attribute flags (e.g primary output,
                                                // direct output...). For outputs only.
            HwModule *mModule;                     // audio HW module exposing this I/O stream
        };

在AudioPolicyManagerBase類物件的mHwModules中儲存了這些讀取的配置。