frameworks/base/media/java/android/media/AudioService.java:
private int getActiveStreamType(int suggestedStreamType) { switch (mPlatformType) { case PLATFORM_VOICE: if (isInCommunication()) { if (AudioSystem.getForceUse(AudioSystem.FOR_COMMUNICATION) == AudioSystem.FORCE_BT_SCO) { // Log.v(TAG, "getActiveStreamType: Forcing STREAM_BLUETOOTH_SCO..."); return AudioSystem.STREAM_BLUETOOTH_SCO; } else { // Log.v(TAG, "getActiveStreamType: Forcing STREAM_VOICE_CALL..."); return AudioSystem.STREAM_VOICE_CALL; } } else if (suggestedStreamType == AudioManager.USE_DEFAULT_STREAM_TYPE) { if (isAfMusicActiveRecently(StreamOverride.sDelayMs)) { if (DEBUG_VOL) Log.v(TAG, "getActiveStreamType: Forcing STREAM_MUSIC stream active"); return AudioSystem.STREAM_MUSIC; } else { if (DEBUG_VOL) Log.v(TAG, "getActiveStreamType: Forcing STREAM_RING b/c default"); //MYRON //return AudioSystem.STREAM_RING; //Log.v(TAG, "[ZHOUXUEWEI] return AudioSystem.STREAM_MUSIC!"); return AudioSystem.STREAM_MUSIC; } } else if (isAfMusicActiveRecently(0)) { if (DEBUG_VOL) Log.v(TAG, "getActiveStreamType: Forcing STREAM_MUSIC stream active"); return AudioSystem.STREAM_MUSIC; } break; case PLATFORM_TELEVISION: if (suggestedStreamType == AudioManager.USE_DEFAULT_STREAM_TYPE) { // TV always defaults to STREAM_MUSIC return AudioSystem.STREAM_MUSIC; } break;