fixes #256 - Webm threads

MediaBrowser.Api/Playback/Progressive/VideoService.cs

@@ -108,7 +108,9 @@ namespace MediaBrowser.Api.Playback.Progressive
                 format = " -f mp4 -movflags frag_keyframe+empty_moov";
             }
 
-            return string.Format("{0} {1} {2} -i {3}{4}{5} {6} {7} -threads 0 {8}{9} \"{10}\"",
+            var threads = string.Equals(videoCodec, "libvpx", StringComparison.OrdinalIgnoreCase) ? 2 : 0;
+
+            return string.Format("{0} {1} {2} -i {3}{4}{5} {6} {7} -threads {8} {9}{10} \"{11}\"",
                 probeSize,
                 GetUserAgentParam(state.Item),
                 GetFastSeekCommandLineParameter(state.Request),
@@ -117,6 +119,7 @@ namespace MediaBrowser.Api.Playback.Progressive
                 keyFrame,
                 GetMapArgs(state),
                 GetVideoArguments(state, videoCodec, performSubtitleConversions),
+                threads,
                 GetAudioArguments(state),
                 format,
                 outputPath