fixes #887 - Support ttml subtitle output

MediaBrowser.Controller/Entities/Audio/Audio.cs

@@ -34,6 +34,11 @@ namespace MediaBrowser.Controller.Entities.Audio
             Tags = new List<string>();
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return LocationType == LocationType.FileSystem && RunTimeTicks.HasValue; }
+        }
+
         /// <summary>
         /// Gets or sets a value indicating whether this instance has embedded image.
         /// </summary>

MediaBrowser.Controller/Entities/Audio/MusicAlbum.cs

@@ -21,6 +21,11 @@ namespace MediaBrowser.Controller.Entities.Audio
             SoundtrackIds = new List<Guid>();
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return true; }
+        }
+
         [IgnoreDataMember]
         public MusicArtist MusicArtist
         {

MediaBrowser.Controller/Entities/Audio/MusicArtist.cs

@@ -26,6 +26,11 @@ namespace MediaBrowser.Controller.Entities.Audio
             }
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return true; }
+        }
+
         protected override IEnumerable<BaseItem> ActualChildren
         {
             get

MediaBrowser.Controller/Entities/Audio/MusicGenre.cs

@@ -18,6 +18,11 @@ namespace MediaBrowser.Controller.Entities.Audio
             return "MusicGenre-" + Name;
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return true; }
+        }
+
         /// <summary>
         /// Returns the folder containing the item.
         /// If the item is a folder, it returns the folder itself

MediaBrowser.Controller/Entities/BaseItem.cs

@@ -52,6 +52,14 @@ namespace MediaBrowser.Controller.Entities
 
         public List<ItemImageInfo> ImageInfos { get; set; }
 
+        public virtual bool SupportsAddingToPlaylist
+        {
+            get
+            {
+                return false;
+            }
+        }
+
         /// <summary>
         /// Gets a value indicating whether this instance is in mixed folder.
         /// </summary>

MediaBrowser.Controller/Entities/TV/Season.cs

@@ -29,6 +29,11 @@ namespace MediaBrowser.Controller.Entities.TV
             }
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return true; }
+        }
+
         [IgnoreDataMember]
         public override bool IsPreSorted
         {

MediaBrowser.Controller/Entities/TV/Series.cs

@@ -39,6 +39,11 @@ namespace MediaBrowser.Controller.Entities.TV
             DisplaySpecialsWithSeasons = true;
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return true; }
+        }
+
         [IgnoreDataMember]
         public override bool IsPreSorted
         {

MediaBrowser.Controller/Entities/Video.cs

@@ -55,6 +55,11 @@ namespace MediaBrowser.Controller.Entities
             LinkedAlternateVersions = new List<LinkedChild>();
         }
 
+        public override bool SupportsAddingToPlaylist
+        {
+            get { return LocationType == LocationType.FileSystem && RunTimeTicks.HasValue; }
+        }
+
         [IgnoreDataMember]
         public int MediaSourceCount
         {