add support for AMD h264_amf & hevc_amf

MediaBrowser.MediaEncoding/Encoder/EncoderValidator.cs

@@ -55,7 +55,9 @@ namespace MediaBrowser.MediaEncoding.Encoder
             "h264_vaapi",
             "hevc_vaapi",
             "h264_v4l2m2m",
-            "ac3"
+            "ac3",
+			"h264_amf",
+			"hevc_amf"
         };
 
         // Try and use the individual library versions to determine a FFmpeg version