Only interact with the AVSampleBufferDisplayLayer on the main thread

Limelight/Stream/Connection.m

@@ -324,6 +324,7 @@ void ClLogMessage(const char* format, ...)
     LiInitializeVideoCallbacks(&_drCallbacks);
     _drCallbacks.setup = DrDecoderSetup;
     _drCallbacks.submitDecodeUnit = DrSubmitDecodeUnit;
+    _drCallbacks.capabilities = CAPABILITY_DIRECT_SUBMIT;
 
     // RFI doesn't work properly with HEVC on iOS 11 with an iPhone SE (at least)
     // It doesnt work on macOS either, tested with Network Link Conditioner.

Limelight/Stream/VideoDecoderRenderer.m

@@ -269,8 +269,13 @@
     if (displayLayer.status == AVQueuedSampleBufferRenderingStatusFailed) {
         Log(LOG_E, @"Display layer rendering failed: %@", displayLayer.error);
         
-        // Recreate the display layer
+        // Recreate the display layer on the main thread.
+        // We need to use dispatch_sync() or we may miss
+        // some parameter sets while the layer is being
+        // recreated.
+        dispatch_sync(dispatch_get_main_queue(), ^{
             [self reinitializeDisplayLayer];
+        });
         
         // Request an IDR frame to initialize the new decoder
         free(data);
@@ -338,13 +343,18 @@
         CFDictionarySetValue(dict, kCMSampleAttachmentKey_DependsOnOthers, kCFBooleanFalse);
     }
 
-    [displayLayer enqueueSampleBuffer:sampleBuffer];
 #if !TARGET_OS_IPHONE
     _view.frameCount++;
 #endif
+
+    // Enqueue video samples on the main thread
+    dispatch_async(dispatch_get_main_queue(), ^{
+        [self->displayLayer enqueueSampleBuffer:sampleBuffer];
+        
         // Dereference the buffers
         CFRelease(blockBuffer);
         CFRelease(sampleBuffer);
+    });
     
     return DR_OK;
 }