diff --git a/SCNVideoWriter/Classes/Error.swift b/SCNVideoWriter/Classes/Error.swift
new file mode 100644
index 0000000..d509e56
--- /dev/null
+++ b/SCNVideoWriter/Classes/Error.swift
@@ -0,0 +1,13 @@
+//
+//  Error.swift
+//  Pods-SCNVideoWriter_Example
+//
+//  Created by Tomoya Hirano on 2017/08/20.
+//
+
+import UIKit
+
+extension SCNVideoWriter {
+  public struct VideoSizeError: Error {}
+}
+
diff --git a/SCNVideoWriter/Classes/Options.swift b/SCNVideoWriter/Classes/Options.swift
new file mode 100644
index 0000000..c8df7cf
--- /dev/null
+++ b/SCNVideoWriter/Classes/Options.swift
@@ -0,0 +1,49 @@
+//
+//  Options.swift
+//  Pods-SCNVideoWriter_Example
+//
+//  Created by Tomoya Hirano on 2017/08/20.
+//
+
+import UIKit
+import AVFoundation
+
+extension SCNVideoWriter {
+  public struct Options {
+    public var timeScale: Int32
+    public var renderSize: CGSize
+    public var videoSize: CGSize
+    public var fps: Int
+    public var outputUrl: URL
+    public var fileType: String
+    public var codec: String
+    public var deleteFileIfExists: Bool
+    
+    public static var `default`: Options {
+      return Options(timeScale: 600,
+                     renderSize: CGSize(width: 640, height: 640),
+                     videoSize: CGSize(width: 1280, height: 720),
+                     fps: 60,
+                     outputUrl: URL(fileURLWithPath: NSTemporaryDirectory() + "output.mp4"),
+                     fileType: AVFileTypeAppleM4V,
+                     codec: AVVideoCodecH264,
+                     deleteFileIfExists: true)
+    }
+    
+    var assetWriterInputSettings: [String : Any] {
+      return [
+        AVVideoCodecKey: codec,
+        AVVideoWidthKey: videoSize.width,
+        AVVideoHeightKey: videoSize.height
+      ]
+    }
+    var sourcePixelBufferAttributes: [String : Any] {
+      return [
+        kCVPixelBufferPixelFormatTypeKey as String: NSNumber(value: kCVPixelFormatType_32ARGB),
+        kCVPixelBufferWidthKey as String: videoSize.width,
+        kCVPixelBufferHeightKey as String: videoSize.height,
+      ]
+    }
+  }
+}
+
diff --git a/SCNVideoWriter/Classes/SCNVideoWriter.swift b/SCNVideoWriter/Classes/SCNVideoWriter.swift
index c518e80..2b9ee93 100644
--- a/SCNVideoWriter/Classes/SCNVideoWriter.swift
+++ b/SCNVideoWriter/Classes/SCNVideoWriter.swift
@@ -43,7 +43,6 @@ public class SCNVideoWriter {
                                     fileType: options.fileType)
     self.input = AVAssetWriterInput(mediaType: AVMediaTypeVideo,
                                     outputSettings: options.assetWriterInputSettings)
-    //input.expectsMediaDataInRealTime = true
     self.pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: input,
                                                                    sourcePixelBufferAttributes: options.sourcePixelBufferAttributes)
     prepare(with: options)
@@ -102,7 +101,7 @@ public class SCNVideoWriter {
     autoreleasepool {
       currentTime = CFAbsoluteTimeGetCurrent() - initialTime
       let image = renderer.snapshot(atTime: currentTime, with: renderSize, antialiasingMode: .multisampling4X)
-      let croppedImage = image.crop(at: videoSize)
+      guard let croppedImage = image.fill(at: videoSize) else { return }
       guard let pixelBuffer = PixelBufferFactory.make(with: videoSize, from: croppedImage, usingBuffer: pool) else { return }
       let value: Int64 = Int64(currentTime * CFTimeInterval(options.timeScale))
       let presentationTime = CMTimeMake(value, options.timeScale)
@@ -117,41 +116,4 @@ public class SCNVideoWriter {
   }
 }
 
-extension SCNVideoWriter {
-  public struct Options {
-    public var timeScale: Int32
-    public var renderSize: CGSize
-    public var videoSize: CGSize
-    public var fps: Int
-    public var outputUrl: URL
-    public var fileType: String
-    public var codec: String
-    public var deleteFileIfExists: Bool
-    
-    public static var `default`: Options {
-      return Options(timeScale: 600,
-                     renderSize: CGSize(width: 640, height: 640),
-                     videoSize: CGSize(width: 640, height: 640),
-                     fps: 60,
-                     outputUrl: URL(fileURLWithPath: NSTemporaryDirectory() + "output.mp4"),
-                     fileType: AVFileTypeAppleM4V,
-                     codec: AVVideoCodecH264,
-                     deleteFileIfExists: true)
-    }
-    
-    var assetWriterInputSettings: [String : Any] {
-      return [
-        AVVideoCodecKey: codec,
-        AVVideoWidthKey: videoSize.width,
-        AVVideoHeightKey: videoSize.height
-      ]
-    }
-    var sourcePixelBufferAttributes: [String : Any] {
-      return [
-        kCVPixelBufferPixelFormatTypeKey as String: NSNumber(value: kCVPixelFormatType_32ARGB),
-        kCVPixelBufferWidthKey as String: videoSize.width,
-        kCVPixelBufferHeightKey as String: videoSize.height
-      ]
-    }
-  }
-}
+
diff --git a/SCNVideoWriter/Classes/UIImage+Extensions.swift b/SCNVideoWriter/Classes/UIImage+Extensions.swift
index 2157910..4262f04 100644
--- a/SCNVideoWriter/Classes/UIImage+Extensions.swift
+++ b/SCNVideoWriter/Classes/UIImage+Extensions.swift
@@ -8,17 +8,52 @@
 import UIKit
 
 extension UIImage {
-  func crop(at size: CGSize) -> UIImage {
+  func fill(at targetSize: CGSize) -> UIImage? {
     let imageSize = self.size
-    let cropSize = size
-    let x = (imageSize.width - cropSize.width) / 2.0
-    let y = (imageSize.height - cropSize.height) / 2.0
-    let cropRect = CGRect(x: x, y: y, width: size.width, height: size.height)
-    return crop(to: cropRect)
-  }
-  
-  func crop(to rect: CGRect) -> UIImage {
-    guard let croppedImageRef = cgImage?.cropping(to: rect) else { return UIImage() }
-    return UIImage(cgImage: croppedImageRef, scale: scale, orientation: .up)
+    let width = imageSize.width
+    let height = imageSize.height
+    let targetWidth = targetSize.width
+    let targetHeight = targetSize.height
+    var scaleFactor: CGFloat = 0.0
+    var scaledWidth = targetWidth
+    var scaledHeight = targetHeight
+    var thumbnailPoint = CGPoint(x: 0, y: 0)
+    
+    if imageSize != targetSize {
+      let widthFactor = targetWidth / width
+      let heightFactor = targetHeight / height
+      
+      if widthFactor > heightFactor {
+        scaleFactor = widthFactor
+      } else {
+        scaleFactor = heightFactor
+      }
+      
+      scaledWidth  = width * scaleFactor
+      scaledHeight = height * scaleFactor
+      
+      if widthFactor > heightFactor {
+        thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5
+      } else {
+        if widthFactor < heightFactor {
+          thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5
+        }
+      }
+    }
+    
+    UIGraphicsBeginImageContext(targetSize)
+    
+    var thumbnailRect = CGRect.zero
+    thumbnailRect.origin = thumbnailPoint
+    thumbnailRect.size.width  = scaledWidth
+    thumbnailRect.size.height = scaledHeight
+    
+    draw(in: thumbnailRect)
+    
+    let newImage = UIGraphicsGetImageFromCurrentImageContext()
+    
+    UIGraphicsEndImageContext()
+    
+    return newImage
   }
 }