Use subtitle cache when burning-in subs

MediaBrowser.Controller/MediaEncoding/EncodingHelper.cs

@@ -1652,13 +1652,15 @@ namespace MediaBrowser.Controller.MediaEncoding
                     setPtsParam);
             }
 
-            var mediaPath = state.MediaPath ?? string.Empty;
+            var subtitlePath = _subtitleEncoder.GetSubtitleFilePath(
+                    state.SubtitleStream,
+                    state.MediaSource,
+                    CancellationToken.None).GetAwaiter().GetResult();
 
             return string.Format(
                 CultureInfo.InvariantCulture,
-                "subtitles=f='{0}':si={1}{2}{3}{4}{5}",
-                _mediaEncoder.EscapeSubtitleFilterPath(mediaPath),
-                state.InternalSubtitleStreamOffset.ToString(CultureInfo.InvariantCulture),
+                "subtitles=f='{0}'{1}{2}{3}{4}",
+                _mediaEncoder.EscapeSubtitleFilterPath(subtitlePath),
                 alphaParam,
                 sub2videoParam,
                 fontParam,

MediaBrowser.Controller/MediaEncoding/ISubtitleEncoder.cs

@@ -44,5 +44,14 @@ namespace MediaBrowser.Controller.MediaEncoding
         /// <param name="cancellationToken">The cancellation token.</param>
         /// <returns>System.String.</returns>
         Task<string> GetSubtitleFileCharacterSet(MediaStream subtitleStream, string language, MediaSourceInfo mediaSource, CancellationToken cancellationToken);
+
+        /// <summary>
+        /// Gets the path to a subtitle file.
+        /// </summary>
+        /// <param name="subtitleStream">The subtitle stream.</param>
+        /// <param name="mediaSource">The media source.</param>
+        /// <param name="cancellationToken">The cancellation token.</param>
+        /// <returns>System.String.</returns>
+        Task<string> GetSubtitleFilePath(MediaStream subtitleStream, MediaSourceInfo mediaSource, CancellationToken cancellationToken);
     }
 }

MediaBrowser.MediaEncoding/Subtitles/SubtitleEncoder.cs

@@ -902,6 +902,12 @@ namespace MediaBrowser.MediaEncoding.Subtitles
             }
         }
 
+        public async Task<string> GetSubtitleFilePath(MediaStream subtitleStream, MediaSourceInfo mediaSource, CancellationToken cancellationToken)
+        {
+            var info = await GetReadableFile(mediaSource, subtitleStream, cancellationToken);
+            return info.Path;
+        }
+
         /// <inheritdoc />
         public void Dispose()
         {