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 c6d429c..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
@@ -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/STKAutoRecoveringHTTPDataSource.h b/StreamingKit/StreamingKit/STKAutoRecoveringHTTPDataSource.h
index f9813ba..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;
@@ -50,3 +52,5 @@ STKAutoRecoveringHTTPDataSourceOptions;
 @property (readonly) STKHTTPDataSource* innerDataSource;
 
 @end
+
+NS_ASSUME_NONNULL_END
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 d91e9e5..cde9b73 100644
--- a/StreamingKit/StreamingKit/STKDataSourceWrapper.h
+++ b/StreamingKit/StreamingKit/STKDataSourceWrapper.h
@@ -34,6 +34,8 @@
 
 #import "STKDataSource.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface STKDataSourceWrapper : STKDataSource<STKDataSourceDelegate>
 
 -(instancetype) initWithDataSource:(STKDataSource*)innerDataSource;
@@ -41,3 +43,5 @@
 @property (readonly) STKDataSource* innerDataSource;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKHTTPDataSource.h b/StreamingKit/StreamingKit/STKHTTPDataSource.h
index d1cc366..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
@@ -54,3 +56,5 @@ typedef void(^STKAsyncURLProvider)(STKHTTPDataSource* dataSource, BOOL forSeek,
 -(void) reconnect;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKLocalFileDataSource.h b/StreamingKit/StreamingKit/STKLocalFileDataSource.h
index ee918c7..581f42d 100644
--- a/StreamingKit/StreamingKit/STKLocalFileDataSource.h
+++ b/StreamingKit/StreamingKit/STKLocalFileDataSource.h
@@ -34,6 +34,8 @@
 
 #import "STKCoreFoundationDataSource.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface STKLocalFileDataSource : STKCoreFoundationDataSource
 
 +(AudioFileTypeID) audioFileTypeHintFromFileExtension:(NSString*)fileExtension;
@@ -41,3 +43,5 @@
 -(instancetype) initWithFilePath:(NSString*)filePath;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/StreamingKit/StreamingKit/STKQueueEntry.h b/StreamingKit/StreamingKit/STKQueueEntry.h
index a5fa781..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
@@ -43,4 +45,6 @@
 -(double) calculatedBitRate;
 -(BOOL) isDefinitelyCompatible:(AudioStreamBasicDescription*)basicDescription;
 
-@end
\ No newline at end of file
+@end
+
+NS_ASSUME_NONNULL_END