Add referer parameter to ffmpeg

As of https://trac.ffmpeg.org/ticket/2179, ffmpeg supports referer parameter which injects Referer header to the HTTP request for remote content. Have EncodingHelper pass this in if it's included in RemoteHttpHeaders.

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -255,6 +255,21 @@ namespace MediaBrowser.Controller.MediaEncoding
             return string.Empty;
         }
 
+        /// <summary>
+        /// Gets the referer param.
+        /// </summary>
+        /// <param name="state">The state.</param>
+        /// <returns>System.String.</returns>
+        public string GetRefererParam(EncodingJobInfo state)
+        {
+            if (state.RemoteHttpHeaders.TryGetValue("Referer", out string referer))
+            {
+                return "-referer \"" + referer + "\"";
+            }
+
+            return string.Empty;
+        }
+
         public static string GetInputFormat(string container)
         {
             if (string.IsNullOrEmpty(container))
@@ -4962,6 +4977,15 @@ namespace MediaBrowser.Controller.MediaEncoding
 
             inputModifier = inputModifier.Trim();
 
+            var refererParam = GetRefererParam(state);
+
+            if (!string.IsNullOrEmpty(refererParam))
+            {
+                inputModifier += " " + refererParam;
+            }
+
+            inputModifier = inputModifier.Trim();
+
             inputModifier += " " + GetFastSeekCommandLineParameter(state, encodingOptions, segmentContainer);
             inputModifier = inputModifier.Trim();