Core Audio: Improvements to iOS.

  * The session category can now be configured via the context config. When
    set to ma_ios_session_category_default, it will try PlayAndRecord,
    Playback and Record (in that order) until one works. If none work it
    leave the category untouched. This will also set the DefaultToSpeaker
    option since in most cases an application will want audio to be emitted
    from the speaker rather than the receiver.  If the application does not
    want to change the session category, use ma_ios_session_category_none.

  * The session category options can now be configured via the context
    config. This maps to the AVAudioSessionCategoryOption flags.

Public issues #101, #113

miniaudio.h

@@ -1880,6 +1880,31 @@ typedef enum
     ma_share_mode_exclusive
 } ma_share_mode;
 
+/* iOS/tvOS/watchOS session categories. */
+typedef enum
+{
+    ma_ios_session_category_default = 0,        /* AVAudioSessionCategoryPlayAndRecord with AVAudioSessionCategoryOptionDefaultToSpeaker. */
+    ma_ios_session_category_none,               /* Leave the session category unchanged. */
+    ma_ios_session_category_ambient,            /* AVAudioSessionCategoryAmbient */
+    ma_ios_session_category_solo_ambient,       /* AVAudioSessionCategorySoloAmbient */
+    ma_ios_session_category_playback,           /* AVAudioSessionCategoryPlayback */
+    ma_ios_session_category_record,             /* AVAudioSessionCategoryRecord */
+    ma_ios_session_category_play_and_record,    /* AVAudioSessionCategoryPlayAndRecord */
+    ma_ios_session_category_multi_route         /* AVAudioSessionCategoryMultiRoute */
+} ma_ios_session_category;
+
+/* iOS/tvOS/watchOS session category options */
+typedef enum
+{
+    ma_ios_session_category_option_mix_with_others                            = 0x01,   /* AVAudioSessionCategoryOptionMixWithOthers */
+    ma_ios_session_category_option_duck_others                                = 0x02,   /* AVAudioSessionCategoryOptionDuckOthers */
+    ma_ios_session_category_option_allow_bluetooth                            = 0x04,   /* AVAudioSessionCategoryOptionAllowBluetooth */
+    ma_ios_session_category_option_default_to_speaker                         = 0x08,   /* AVAudioSessionCategoryOptionDefaultToSpeaker */
+    ma_ios_session_category_option_interrupt_spoken_audio_and_mix_with_others = 0x11,   /* AVAudioSessionCategoryOptionInterruptSpokenAudioAndMixWithOthers */
+    ma_ios_session_category_option_allow_bluetooth_a2dp                       = 0x20,   /* AVAudioSessionCategoryOptionAllowBluetoothA2DP */
+    ma_ios_session_category_option_allow_air_play                             = 0x40,   /* AVAudioSessionCategoryOptionAllowAirPlay */
+} ma_ios_session_category_option;
+
 typedef union
 {
 #ifdef MA_SUPPORT_WASAPI
@@ -2018,7 +2043,8 @@ typedef struct
     } pulse;
     struct
     {
-        ma_bool32 noBluetoothRouting;
+        ma_ios_session_category sessionCategory;
+        ma_uint32 sessionCategoryOptions;
     } coreaudio;
     struct
     {
@@ -17952,7 +17978,6 @@ Core Audio Backend
 #include <CoreAudio/CoreAudio.h>
 #else
 #include <AVFoundation/AVFoundation.h>
-#include <UIKit/UIKit.h>  /* For [UIDevice currentDevice] */
 #endif
 
 #include <AudioToolbox/AudioToolbox.h>
@@ -20576,39 +20601,62 @@ ma_result ma_context_uninit__coreaudio(ma_context* pContext)
     return MA_SUCCESS;
 }
 
+static AVAudioSessionCategory ma_to_AVAudioSessionCategory(ma_ios_session_category category)
+{
+    /* The "default" and "none" categories are treated different and should not be used as an input into this function. */
+    ma_assert(category != ma_ios_session_category_default);
+    ma_assert(category != ma_ios_session_category_none);
+
+    switch (category) {
+        case ma_ios_session_category_ambient:         return AVAudioSessionCategoryAmbient;
+        case ma_ios_session_category_solo_ambient:    return AVAudioSessionCategorySoloAmbient;
+        case ma_ios_session_category_playback:        return AVAudioSessionCategoryPlayback;
+        case ma_ios_session_category_record:          return AVAudioSessionCategoryRecord;
+        case ma_ios_session_category_play_and_record: return AVAudioSessionCategoryPlayAndRecord;
+        case ma_ios_session_category_multi_route:     return AVAudioSessionCategoryMultiRoute;
+        case ma_ios_session_category_none:            return AVAudioSessionCategoryAmbient;
+        case ma_ios_session_category_default:         return AVAudioSessionCategoryAmbient;
+        default:                                      return AVAudioSessionCategoryAmbient;
+    }
+}
+
 ma_result ma_context_init__coreaudio(const ma_context_config* pConfig, ma_context* pContext)
 {
+    ma_assert(pConfig != NULL);
     ma_assert(pContext != NULL);
 
-    (void)pConfig;
-
 #if defined(MA_APPLE_MOBILE)
     @autoreleasepool {
         AVAudioSession* pAudioSession = [AVAudioSession sharedInstance];
-        AVAudioSessionCategoryOptions options = 0;
+        AVAudioSessionCategoryOptions options = pConfig->coreaudio.sessionCategoryOptions;
 
         ma_assert(pAudioSession != NULL);
 
-        /*
-        Try enabling routing to Bluetooth devices. The AVAudioSessionCategoryOptionAllowBluetoothA2DP is only available
-        starting from iOS 10 so I'm doing a version check before enabling this.
-        */
-        if (!pConfig->coreaudio.noBluetoothRouting) {
-            if ([[[UIDevice currentDevice] systemVersion] compare:@"10.0" options:NSNumericSearch] != NSOrderedAscending) {
-                options = 0x20; /* 0x20 = AVAudioSessionCategoryOptionAllowBluetoothA2DP */
-            }
-        }
+        if (pConfig->coreaudio.sessionCategory == ma_ios_session_category_default) {
+            /*
+            I'm going to use trial and error to determine our default session category. First we'll try PlayAndRecord. If that fails
+            we'll try Playback and if that fails we'll try record. If all of these fail we'll just not set the category.
+            */
+        #if !defined(MA_APPLE_TV) && !defined(MA_APPLE_WATCH)
+            options |= AVAudioSessionCategoryOptionDefaultToSpeaker;
+        #endif
 
-        [pAudioSession setCategory: AVAudioSessionCategoryPlayAndRecord withOptions:options error:nil];
-        
-        /* AVAudioSessionPortOverrideSpeaker is not available on Apple TV OS nor Apple Watch OS. */
-    #if !defined(MA_APPLE_TV) && !defined(MA_APPLE_WATCH)
-        /* By default we want miniaudio to use the speakers instead of the receiver. In the future this may be customizable. */
-        ma_bool32 useSpeakers = MA_TRUE;
-        if (useSpeakers) {
-            [pAudioSession overrideOutputAudioPort:AVAudioSessionPortOverrideSpeaker error:nil];
+            if ([pAudioSession setCategory: AVAudioSessionCategoryPlayAndRecord withOptions:options error:nil]) {
+                /* Using PlayAndRecord */
+            } else if ([pAudioSession setCategory: AVAudioSessionCategoryPlayback withOptions:options error:nil]) {
+                /* Using Playback */
+            } else if ([pAudioSession setCategory: AVAudioSessionCategoryRecord withOptions:options error:nil]) {
+                /* Using Record */
+            } else {
+                /* Leave as default? */
+            }
+        } else {
+            if (pConfig->coreaudio.sessionCategory != ma_ios_session_category_none) {
+                if (![pAudioSession setCategory: ma_to_AVAudioSessionCategory(pConfig->coreaudio.sessionCategory) withOptions:options error:nil]) {
+                    return MA_INVALID_OPERATION;    /* Failed to set session category. */
+                }
+            }
         }
-    #endif
     }
 #endif
     
@@ -20618,8 +20666,8 @@ ma_result ma_context_init__coreaudio(const ma_context_config* pConfig, ma_contex
         return MA_API_NOT_FOUND;
     }
     
-    pContext->coreaudio.CFStringGetCString             = ma_dlsym(pContext, pContext->coreaudio.hCoreFoundation, "CFStringGetCString");
-    pContext->coreaudio.CFRelease                      = ma_dlsym(pContext, pContext->coreaudio.hCoreFoundation, "CFRelease");
+    pContext->coreaudio.CFStringGetCString = ma_dlsym(pContext, pContext->coreaudio.hCoreFoundation, "CFStringGetCString");
+    pContext->coreaudio.CFRelease          = ma_dlsym(pContext, pContext->coreaudio.hCoreFoundation, "CFRelease");
     
     
     pContext->coreaudio.hCoreAudio = ma_dlopen(pContext, "CoreAudio.framework/CoreAudio");