Use nullable enum type instead of strings

MediaBrowser.Model/Session/HardwareEncodingType.cs

@@ -0,0 +1,48 @@
+namespace MediaBrowser.Model.Session
+{
+    /// <summary>
+    /// Enum HardwareEncodingType.
+    /// </summary>
+    public enum HardwareEncodingType
+    {
+        /// <summary>
+        /// AMD AMF
+        /// </summary>
+        AMF,
+
+        /// <summary>
+        /// Intel Quick Sync Video
+        /// </summary>
+        QSV,
+
+        /// <summary>
+        /// NVIDIA NVENC
+        /// </summary>
+        NVENC,
+
+        /// <summary>
+        /// OpenMax OMX
+        /// </summary>
+        OMX,
+
+        /// <summary>
+        /// Exynos V4L2 MFC
+        /// </summary>
+        V4L2M2M,
+
+        /// <summary>
+        /// MediaCodec Android
+        /// </summary>
+        MediaCodec,
+
+        /// <summary>
+        /// Video Acceleration API (VAAPI)
+        /// </summary>
+        VAAPI,
+
+        /// <summary>
+        /// Video ToolBox
+        /// </summary>
+        VideoToolBox
+    }
+}