Android audio设备的定义
Audio设备的定义位于framework中，分为C++层和Java层的定义。Java层的定义对第三方应用不可见，即通过标准API无法使用。
1.C++中audio设备的定义
audio设备的定义在2.3.7及之前是位于frameworks/base/include/media目录下的AudioSystem.h文件中。
在ics4.0及以后是移到了hardware/libhardware_legacy/include/hardware_legacy目录下的AudioSystemLegacy.h文件中，
但此定义在4.2中已经废弃，需要使用/system/core/include/system/audio.h中的定义。audio.h中音频设备定义如下：
enum {
AUDIO_DEVICE_NONE = 0x0,
/* reserved bits */
AUDIO_DEVICE_BIT_IN = 0x80000000,
AUDIO_DEVICE_BIT_DEFAULT = 0x40000000,
/* output devices */
AUDIO_DEVICE_OUT_EARPIECE = 0x1, // 听筒
AUDIO_DEVICE_OUT_SPEAKER = 0x2, // 扬声器
AUDIO_DEVICE_OUT_WIRED_HEADSET = 0x4, // 线控耳机，可以通过耳机控制远端播放、暂停、音量调节等功能的耳机
AUDIO_DEVICE_OUT_WIRED_HEADPHONE = 0x8, // 普通耳机，只能听，不能操控播放
AUDIO_DEVICE_OUT_BLUETOOTH_SCO = 0x10, // 单声道蓝牙耳机，十进制32
AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET = 0x20, // 车载免提蓝牙设备，十进制64
AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT = 0x40, // 立体声蓝牙耳机
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP = 0x80, // 十进制128
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES = 0x100, // 十进制256
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER = 0x200, // 十进制512
AUDIO_DEVICE_OUT_AUX_DIGITAL = 0x400, // 十进制1024
AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET = 0x800, // 十进制2048
AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET = 0x1000, // 十进制4096
AUDIO_DEVICE_OUT_USB_ACCESSORY = 0x2000,
AUDIO_DEVICE_OUT_USB_DEVICE = 0x4000,
AUDIO_DEVICE_OUT_REMOTE_SUBMIX = 0x8000,
AUDIO_DEVICE_OUT_DEFAULT = AUDIO_DEVICE_BIT_DEFAULT,
AUDIO_DEVICE_OUT_ALL = (AUDIO_DEVICE_OUT_EARPIECE |
AUDIO_DEVICE_OUT_SPEAKER |
AUDIO_DEVICE_OUT_WIRED_HEADSET |
AUDIO_DEVICE_OUT_WIRED_HEADPHONE |
AUDIO_DEVICE_OUT_BLUETOOTH_SCO |
AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET |
AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT |
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP |
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER |
AUDIO_DEVICE_OUT_AUX_DIGITAL |
AUDIO_DEVICE_OUT_ANLG_DOCK_HEADSET |
AUDIO_DEVICE_OUT_DGTL_DOCK_HEADSET |
AUDIO_DEVICE_OUT_USB_ACCESSORY |
AUDIO_DEVICE_OUT_USB_DEVICE |
AUDIO_DEVICE_OUT_REMOTE_SUBMIX |
AUDIO_DEVICE_OUT_DEFAULT),
AUDIO_DEVICE_OUT_ALL_A2DP = (AUDIO_DEVICE_OUT_BLUETOOTH_A2DP |
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES |
AUDIO_DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER),
AUDIO_DEVICE_OUT_ALL_SCO = (AUDIO_DEVICE_OUT_BLUETOOTH_SCO |
AUDIO_DEVICE_OUT_BLUETOOTH_SCO_HEADSET |
AUDIO_DEVICE_OUT_BLUETOOTH_SCO_CARKIT),
AUDIO_DEVICE_OUT_ALL_USB = (AUDIO_DEVICE_OUT_USB_ACCESSORY |
AUDIO_DEVICE_OUT_USB_DEVICE),
/* input devices */
AUDIO_DEVICE_IN_COMMUNICATION = AUDIO_DEVICE_BIT_IN | 0x1,
AUDIO_DEVICE_IN_AMBIENT = AUDIO_DEVICE_BIT_IN | 0x2,
AUDIO_DEVICE_IN_BUILTIN_MIC = AUDIO_DEVICE_BIT_IN | 0x4, //手机自带MIC
AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET = AUDIO_DEVICE_BIT_IN | 0x8,
AUDIO_DEVICE_IN_WIRED_HEADSET = AUDIO_DEVICE_BIT_IN | 0x10, //耳机
AUDIO_DEVICE_IN_AUX_DIGITAL = AUDIO_DEVICE_BIT_IN | 0x20,
AUDIO_DEVICE_IN_VOICE_CALL = AUDIO_DEVICE_BIT_IN | 0x40,
AUDIO_DEVICE_IN_BACK_MIC = AUDIO_DEVICE_BIT_IN | 0x80,
AUDIO_DEVICE_IN_REMOTE_SUBMIX = AUDIO_DEVICE_BIT_IN | 0x100,
AUDIO_DEVICE_IN_ANLG_DOCK_HEADSET = AUDIO_DEVICE_BIT_IN | 0x200,
AUDIO_DEVICE_IN_DGTL_DOCK_HEADSET = AUDIO_DEVICE_BIT_IN | 0x400,
AUDIO_DEVICE_IN_USB_ACCESSORY = AUDIO_DEVICE_BIT_IN | 0x800,
AUDIO_DEVICE_IN_USB_DEVICE = AUDIO_DEVICE_BIT_IN | 0x1000,
AUDIO_DEVICE_IN_DEFAULT = AUDIO_DEVICE_BIT_IN | AUDIO_DEVICE_BIT_DEFAULT,
AUDIO_DEVICE_IN_ALL = (AUDIO_DEVICE_IN_COMMUNICATION |
AUDIO_DEVICE_IN_AMBIENT |
AUDIO_DEVICE_IN_BUILTIN_MIC |
AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET |
AUDIO_DEVICE_IN_WIRED_HEADSET |
AUDIO_DEVICE_IN_AUX_DIGITAL |
AUDIO_DEVICE_IN_VOICE_CALL |
AUDIO_DEVICE_IN_BACK_MIC |
AUDIO_DEVICE_IN_REMOTE_SUBMIX |
AUDIO_DEVICE_IN_ANLG_DOCK_HEADSET |
AUDIO_DEVICE_IN_DGTL_DOCK_HEADSET |
AUDIO_DEVICE_IN_USB_ACCESSORY |
AUDIO_DEVICE_IN_USB_DEVICE |
AUDIO_DEVICE_IN_DEFAULT),
AUDIO_DEVICE_IN_ALL_SCO = AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET,
};2.java中aduio设备的定义
java中对audio设备的定义位于AudioManager.java中，实际是在AudioSystem.java中定义的。
// This section re-defines new output device constants from AudioSystem, because the AudioSystem
// class is not used by other parts of the framework, which instead use definitions and methods
// from AudioManager. AudioSystem is an internal class used by AudioManager and AudioService.
/** {@hide} The audio output device code for the small speaker at the front of the device used
* when placing calls. Does not refer to an in-ear headphone without attached microphone,
* such as earbuds, earphones, or in-ear monitors (IEM). Those would be handled as a
* {@link #DEVICE_OUT_WIRED_HEADPHONE}.
*/
public static final int DEVICE_OUT_EARPIECE = AudioSystem.DEVICE_OUT_EARPIECE;
/** {@hide} The audio output device code for the built-in speaker */
public static final int DEVICE_OUT_SPEAKER = AudioSystem.DEVICE_OUT_SPEAKER;
/** {@hide} The audio output device code for a wired headset with attached microphone */
public static final int DEVICE_OUT_WIRED_HEADSET = AudioSystem.DEVICE_OUT_WIRED_HEADSET;
/** {@hide} The audio output device code for a wired headphone without attached microphone */
public static final int DEVICE_OUT_WIRED_HEADPHONE = AudioSystem.DEVICE_OUT_WIRED_HEADPHONE;
/** {@hide} The audio output device code for generic Bluetooth SCO, for voice */
public static final int DEVICE_OUT_BLUETOOTH_SCO = AudioSystem.DEVICE_OUT_BLUETOOTH_SCO;
/** {@hide} The audio output device code for Bluetooth SCO Headset Profile (HSP) and
* Hands-Free Profile (HFP), for voice
*/
public static final int DEVICE_OUT_BLUETOOTH_SCO_HEADSET =
AudioSystem.DEVICE_OUT_BLUETOOTH_SCO_HEADSET;
/** {@hide} The audio output device code for Bluetooth SCO car audio, for voice */
public static final int DEVICE_OUT_BLUETOOTH_SCO_CARKIT =
AudioSystem.DEVICE_OUT_BLUETOOTH_SCO_CARKIT;
/** {@hide} The audio output device code for generic Bluetooth A2DP, for music */
public static final int DEVICE_OUT_BLUETOOTH_A2DP = AudioSystem.DEVICE_OUT_BLUETOOTH_A2DP;
/** {@hide} The audio output device code for Bluetooth A2DP headphones, for music */
public static final int DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES =
AudioSystem.DEVICE_OUT_BLUETOOTH_A2DP_HEADPHONES;
/** {@hide} The audio output device code for Bluetooth A2DP external speaker, for music */
public static final int DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER =
AudioSystem.DEVICE_OUT_BLUETOOTH_A2DP_SPEAKER;
/** {@hide} The audio output device code for S/PDIF or HDMI */
public static final int DEVICE_OUT_AUX_DIGITAL = AudioSystem.DEVICE_OUT_AUX_DIGITAL;
/** {@hide} The audio output device code for an analog wired headset attached via a
* docking station
*/
public static final int DEVICE_OUT_ANLG_DOCK_HEADSET = AudioSystem.DEVICE_OUT_ANLG_DOCK_HEADSET;
/** {@hide} The audio output device code for a digital wired headset attached via a
* docking station
*/
public static final int DEVICE_OUT_DGTL_DOCK_HEADSET = AudioSystem.DEVICE_OUT_DGTL_DOCK_HEADSET;
/** {@hide} The audio output device code for a USB audio accessory. The accessory is in USB host
* mode and the Android device in USB device mode
*/
public static final int DEVICE_OUT_USB_ACCESSORY = AudioSystem.DEVICE_OUT_USB_ACCESSORY;
/** {@hide} The audio output device code for a USB audio device. The device is in USB device
* mode and the Android device in USB host mode
*/
public static final int DEVICE_OUT_USB_DEVICE = AudioSystem.DEVICE_OUT_USB_DEVICE;
/** {@hide} This is not used as a returned value from {@link #getDevicesForStream}, but could be
* used in the future in a set method to select whatever default device is chosen by the
* platform-specific implementation.
*/
public static final int DEVICE_OUT_DEFAULT = AudioSystem.DEVICE_OUT_DEFAULT;