diff --git a/StreamingKit/StreamingKit/NSMutableArray+STKAudioPlayer.h b/StreamingKit/StreamingKit/NSMutableArray+STKAudioPlayer.h
index 12ca839..1e4de5f 100644
--- a/StreamingKit/StreamingKit/NSMutableArray+STKAudioPlayer.h
+++ b/StreamingKit/StreamingKit/NSMutableArray+STKAudioPlayer.h
@@ -8,10 +8,14 @@
 
 #import <Foundation/Foundation.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface NSMutableArray (STKAudioPlayer)
 -(void) enqueue:(id)obj;
 -(void) skipQueue:(id)obj;
 -(void) skipQueueWithQueue:(NSMutableArray*)queue;
--(id) dequeue;
--(id) peek;
+-(nullable id) dequeue;
+-(nullable id) peek;
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKAudioPlayer.h b/StreamingKit/StreamingKit/STKAudioPlayer.h
index 5c268ef..a1ff3b5 100644
--- a/StreamingKit/StreamingKit/STKAudioPlayer.h
+++ b/StreamingKit/StreamingKit/STKAudioPlayer.h
@@ -44,6 +44,8 @@
 #include "UIKit/UIApplication.h"
 #endif
 
+NS_ASSUME_NONNULL_BEGIN
+
 typedef NS_OPTIONS(NSInteger, STKAudioPlayerState)
 {
     STKAudioPlayerStateReady,
@@ -151,13 +153,13 @@ typedef void(^STKFrameFilter)(UInt32 channelsPerFrame, UInt32 bytesPerFrame, UIn
 /// Enables or disables the EQ
 @property (readwrite) BOOL equalizerEnabled;
 /// Returns an array of STKFrameFilterEntry objects representing the filters currently in use
-@property (readonly) NSArray* frameFilters;
+@property (readonly, nullable) NSArray* frameFilters;
 /// Returns the items pending to be played (includes buffering and upcoming items but does not include the current item)
 @property (readonly) NSArray* pendingQueue;
 /// The number of items pending to be played (includes buffering and upcoming items but does not include the current item)
 @property (readonly) NSUInteger pendingQueueCount;
 /// Gets the most recently queued item that is still pending to play
-@property (readonly) NSObject* mostRecentlyQueuedStillPendingItem;
+@property (readonly, nullable) NSObject* mostRecentlyQueuedStillPendingItem;
 /// Gets the current state of the player
 @property (readwrite) STKAudioPlayerState state;
 /// Gets the options provided to the player on startup
@@ -174,10 +176,10 @@ typedef void(^STKFrameFilter)(UInt32 channelsPerFrame, UInt32 bytesPerFrame, UIn
 +(STKDataSource*) dataSourceFromURL:(NSURL*)url;
 
 /// Initializes a new STKAudioPlayer with the default options
--(id) init;
+-(instancetype) init;
 
 /// Initializes a new STKAudioPlayer with the given options
--(id) initWithOptions:(STKAudioPlayerOptions)optionsIn;
+-(instancetype) initWithOptions:(STKAudioPlayerOptions)optionsIn;
 
 /// Plays an item from the given URL string (all pending queued items are removed).
 /// The NSString is used as the queue item ID
@@ -254,7 +256,7 @@ typedef void(^STKFrameFilter)(UInt32 channelsPerFrame, UInt32 bytesPerFrame, UIn
 
 /// Appends a frame filter with the given name and filter block just after the filter with the given name.
 /// If the given name is nil, the filter will be inserted at the beginning of the filter change
--(void) addFrameFilterWithName:(NSString*)name afterFilterWithName:(NSString*)afterFilterWithName block:(STKFrameFilter)block;
+-(void) addFrameFilterWithName:(NSString*)name afterFilterWithName:(nullable NSString*)afterFilterWithName block:(STKFrameFilter)block;
 
 /// Reads the peak power in decibals for the given channel (0 or 1).
 /// Return values are between -60 (low) and 0 (high).
@@ -268,3 +270,5 @@ typedef void(^STKFrameFilter)(UInt32 channelsPerFrame, UInt32 bytesPerFrame, UIn
 -(void) setGain:(float)gain forEqualizerBand:(int)bandIndex;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKAudioPlayer.m b/StreamingKit/StreamingKit/STKAudioPlayer.m
index 0dac272..2ed83c8 100755
--- a/StreamingKit/StreamingKit/STKAudioPlayer.m
+++ b/StreamingKit/StreamingKit/STKAudioPlayer.m
@@ -173,7 +173,7 @@ STKAudioPlayerInternalState;
 @end
 
 @implementation STKFrameFilterEntry
--(id) initWithFilter:(STKFrameFilter)filterIn andName:(NSString*)nameIn
+-(instancetype) initWithFilter:(STKFrameFilter)filterIn andName:(NSString*)nameIn
 {
 	if (self = [super init])
 	{
@@ -504,12 +504,12 @@ static void AudioFileStreamPacketsProc(void* clientData, UInt32 numberBytes, UIn
     }
 }
 
--(id) init
+-(instancetype) init
 {
     return [self initWithOptions:(STKAudioPlayerOptions){}];
 }
 
--(id) initWithOptions:(STKAudioPlayerOptions)optionsIn
+-(instancetype) initWithOptions:(STKAudioPlayerOptions)optionsIn
 {
     if (self = [super init])
     {
diff --git a/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.h b/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.h
index c55895f..bab707b 100644
--- a/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.h
+++ b/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.h
@@ -36,6 +36,8 @@
 #import "STKHTTPDataSource.h"
 #import "STKDataSourceWrapper.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 typedef struct
 {
     int watchdogPeriodSeconds;
@@ -45,8 +47,10 @@ STKAutoRecoveringHTTPDataSourceOptions;
 
 @interface STKAutoRecoveringHTTPDataSource : STKDataSourceWrapper
 
--(id) initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSource;
+-(instancetype) initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSource;
 
 @property (readonly) STKHTTPDataSource* innerDataSource;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.m b/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.m
index 445d44d..8dfe3a8 100644
--- a/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.m
+++ b/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.m
@@ -108,17 +108,17 @@ static void PopulateOptionsWithDefault(STKAutoRecoveringHTTPDataSourceOptions* o
     return (STKHTTPDataSource*)self.innerDataSource;
 }
 
--(id) initWithDataSource:(STKDataSource *)innerDataSource
+-(instancetype) initWithDataSource:(STKDataSource *)innerDataSource
 {
     return [self initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSource];
 }
 
--(id) initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSourceIn
+-(instancetype) initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSourceIn
 {
     return [self initWithHTTPDataSource:innerDataSourceIn andOptions:(STKAutoRecoveringHTTPDataSourceOptions){}];
 }
 
--(id) initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSourceIn andOptions:(STKAutoRecoveringHTTPDataSourceOptions)optionsIn
+-(instancetype) initWithHTTPDataSource:(STKHTTPDataSource*)innerDataSourceIn andOptions:(STKAutoRecoveringHTTPDataSourceOptions)optionsIn
 {
     if (self = [super initWithDataSource:innerDataSourceIn])
     {
diff --git a/StreamingKit/StreamingKit/STKCoreFoundationDataSource.h b/StreamingKit/StreamingKit/STKCoreFoundationDataSource.h
index b25a72e..b1dd325 100644
--- a/StreamingKit/StreamingKit/STKCoreFoundationDataSource.h
+++ b/StreamingKit/StreamingKit/STKCoreFoundationDataSource.h
@@ -34,6 +34,8 @@
 
 #import "STKDataSource.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class STKCoreFoundationDataSource;
 
 @interface CoreFoundationDataSourceClientInfo : NSObject
@@ -62,3 +64,5 @@
 -(CFStreamStatus) status;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKDataSource.h b/StreamingKit/StreamingKit/STKDataSource.h
index 8ca4150..0a1e716 100755
--- a/StreamingKit/StreamingKit/STKDataSource.h
+++ b/StreamingKit/StreamingKit/STKDataSource.h
@@ -35,6 +35,8 @@
 #import <Foundation/Foundation.h>
 #include <AudioToolbox/AudioToolbox.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class STKDataSource;
 
 @protocol STKDataSourceDelegate<NSObject>
@@ -50,8 +52,8 @@
 @property (readonly) SInt64 length;
 @property (readonly) BOOL hasBytesAvailable;
 @property (nonatomic, readwrite, assign) double durationHint;
-@property (readwrite, unsafe_unretained) id<STKDataSourceDelegate> delegate;
-@property (nonatomic, strong) NSURL *recordToFileUrl;
+@property (readwrite, unsafe_unretained, nullable) id<STKDataSourceDelegate> delegate;
+@property (nonatomic, strong, nullable) NSURL *recordToFileUrl;
 
 -(BOOL) registerForEvents:(NSRunLoop*)runLoop;
 -(void) unregisterForEvents;
@@ -62,3 +64,5 @@
 -(AudioFileTypeID) audioFileTypeHint;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKDataSourceWrapper.h b/StreamingKit/StreamingKit/STKDataSourceWrapper.h
index 4d3e035..cde9b73 100644
--- a/StreamingKit/StreamingKit/STKDataSourceWrapper.h
+++ b/StreamingKit/StreamingKit/STKDataSourceWrapper.h
@@ -34,10 +34,14 @@
 
 #import "STKDataSource.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface STKDataSourceWrapper : STKDataSource<STKDataSourceDelegate>
 
--(id) initWithDataSource:(STKDataSource*)innerDataSource;
+-(instancetype) initWithDataSource:(STKDataSource*)innerDataSource;
 
 @property (readonly) STKDataSource* innerDataSource;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKDataSourceWrapper.m b/StreamingKit/StreamingKit/STKDataSourceWrapper.m
index 76e1634..c75a499 100644
--- a/StreamingKit/StreamingKit/STKDataSourceWrapper.m
+++ b/StreamingKit/StreamingKit/STKDataSourceWrapper.m
@@ -40,7 +40,7 @@
 
 @implementation STKDataSourceWrapper
 
--(id) initWithDataSource:(STKDataSource*)innerDataSourceIn
+-(instancetype) initWithDataSource:(STKDataSource*)innerDataSourceIn
 {
     if (self = [super init])
     {
diff --git a/StreamingKit/StreamingKit/STKHTTPDataSource.h b/StreamingKit/StreamingKit/STKHTTPDataSource.h
index 9bf7002..691bbff 100644
--- a/StreamingKit/StreamingKit/STKHTTPDataSource.h
+++ b/StreamingKit/StreamingKit/STKHTTPDataSource.h
@@ -34,10 +34,12 @@
 
 #import "STKCoreFoundationDataSource.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class STKHTTPDataSource;
 
 typedef void(^STKURLBlock)(NSURL* url);
-typedef NSURL*(^STKURLProvider)();
+typedef NSURL* _Nonnull (^STKURLProvider)();
 typedef void(^STKAsyncURLProvider)(STKHTTPDataSource* dataSource, BOOL forSeek, STKURLBlock callback);
 
 @interface STKHTTPDataSource : STKCoreFoundationDataSource
@@ -46,11 +48,13 @@ typedef void(^STKAsyncURLProvider)(STKHTTPDataSource* dataSource, BOOL forSeek,
 @property (readonly) UInt32 httpStatusCode;
 
 +(AudioFileTypeID) audioFileTypeHintFromMimeType:(NSString*)fileExtension;
--(id) initWithURL:(NSURL*)url;
--(id) initWithURL:(NSURL *)url httpRequestHeaders:(NSDictionary *)httpRequestHeaders;
--(id) initWithURLProvider:(STKURLProvider)urlProvider;
--(id) initWithAsyncURLProvider:(STKAsyncURLProvider)asyncUrlProvider;
--(NSRunLoop*) eventsRunLoop;
+-(instancetype) initWithURL:(NSURL*)url;
+-(instancetype) initWithURL:(NSURL*)url httpRequestHeaders:(NSDictionary*)httpRequestHeaders;
+-(instancetype) initWithURLProvider:(STKURLProvider)urlProvider;
+-(instancetype) initWithAsyncURLProvider:(STKAsyncURLProvider)asyncUrlProvider;
+-(nullable NSRunLoop*) eventsRunLoop;
 -(void) reconnect;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKHTTPDataSource.m b/StreamingKit/StreamingKit/STKHTTPDataSource.m
index bd66ab5..47d4a48 100755
--- a/StreamingKit/StreamingKit/STKHTTPDataSource.m
+++ b/StreamingKit/StreamingKit/STKHTTPDataSource.m
@@ -64,19 +64,19 @@
 
 @implementation STKHTTPDataSource
 
--(id) initWithURL:(NSURL*)urlIn
+-(instancetype) initWithURL:(NSURL*)urlIn
 {
     return [self initWithURLProvider:^NSURL* { return urlIn; }];
 }
 
--(id) initWithURL:(NSURL *)urlIn httpRequestHeaders:(NSDictionary *)httpRequestHeaders
+-(instancetype) initWithURL:(NSURL *)urlIn httpRequestHeaders:(NSDictionary *)httpRequestHeaders
 {
     self = [self initWithURLProvider:^NSURL* { return urlIn; }];
     self->requestHeaders = httpRequestHeaders;
     return self;
 }
 
--(id) initWithURLProvider:(STKURLProvider)urlProviderIn
+-(instancetype) initWithURLProvider:(STKURLProvider)urlProviderIn
 {
 	urlProviderIn = [urlProviderIn copy];
     
@@ -86,7 +86,7 @@
     }];
 }
 
--(id) initWithAsyncURLProvider:(STKAsyncURLProvider)asyncUrlProviderIn
+-(instancetype) initWithAsyncURLProvider:(STKAsyncURLProvider)asyncUrlProviderIn
 {
     if (self = [super init])
     {
diff --git a/StreamingKit/StreamingKit/STKLocalFileDataSource.h b/StreamingKit/StreamingKit/STKLocalFileDataSource.h
index 2a5f571..581f42d 100644
--- a/StreamingKit/StreamingKit/STKLocalFileDataSource.h
+++ b/StreamingKit/StreamingKit/STKLocalFileDataSource.h
@@ -34,10 +34,14 @@
 
 #import "STKCoreFoundationDataSource.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface STKLocalFileDataSource : STKCoreFoundationDataSource
 
 +(AudioFileTypeID) audioFileTypeHintFromFileExtension:(NSString*)fileExtension;
 @property (readonly, copy) NSString* filePath;
--(id) initWithFilePath:(NSString*)filePath;
+-(instancetype) initWithFilePath:(NSString*)filePath;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKLocalFileDataSource.m b/StreamingKit/StreamingKit/STKLocalFileDataSource.m
index 2aded28..afdd2fd 100644
--- a/StreamingKit/StreamingKit/STKLocalFileDataSource.m
+++ b/StreamingKit/StreamingKit/STKLocalFileDataSource.m
@@ -47,7 +47,7 @@
 @implementation STKLocalFileDataSource
 @synthesize filePath;
 
--(id) initWithFilePath:(NSString*)filePathIn
+-(instancetype) initWithFilePath:(NSString*)filePathIn
 {
     if (self = [super init])
     {
diff --git a/StreamingKit/StreamingKit/STKQueueEntry.h b/StreamingKit/StreamingKit/STKQueueEntry.h
index 3ae6f6a..f13d277 100755
--- a/StreamingKit/StreamingKit/STKQueueEntry.h
+++ b/StreamingKit/StreamingKit/STKQueueEntry.h
@@ -10,6 +10,8 @@
 #import "libkern/OSAtomic.h"
 #import "AudioToolbox/AudioToolbox.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface STKQueueEntry : NSObject
 {
 @public
@@ -35,7 +37,7 @@
 @property (readwrite, retain) NSObject* queueItemId;
 @property (readwrite, retain) STKDataSource* dataSource;
 
--(id) initWithDataSource:(STKDataSource*)dataSource andQueueItemId:(NSObject*)queueItemId;
+-(instancetype) initWithDataSource:(STKDataSource*)dataSource andQueueItemId:(NSObject*)queueItemId;
 
 -(void) reset;
 -(double) duration;
@@ -43,4 +45,6 @@
 -(double) calculatedBitRate;
 -(BOOL) isDefinitelyCompatible:(AudioStreamBasicDescription*)basicDescription;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKQueueEntry.m b/StreamingKit/StreamingKit/STKQueueEntry.m
index b5c351b..0c1d1e3 100755
--- a/StreamingKit/StreamingKit/STKQueueEntry.m
+++ b/StreamingKit/StreamingKit/STKQueueEntry.m
@@ -14,7 +14,7 @@
 
 @implementation STKQueueEntry
 
--(id) initWithDataSource:(STKDataSource*)dataSourceIn andQueueItemId:(NSObject*)queueItemIdIn
+-(instancetype) initWithDataSource:(STKDataSource*)dataSourceIn andQueueItemId:(NSObject*)queueItemIdIn
 {
     if (self = [super init])
     {
@@ -121,4 +121,4 @@
     return [[self queueItemId] description];
 }
 
-@end
\ No newline at end of file
+@end