ARC forbids explicit message send of 'release'; since iOS 6 even for dispatch_release() calls: stripping it out in those cases is required. Use iOS 6 version value instead of macro for comparisons because we might get compiled on an old OS that does not define a later.
AVAssetWriter –finishWriting is deprecated in iOS 6.0; switch over to the new -finishWritingWithCompletionHandler: for that version and up.