add hls segmenter streaming mode (#400)

* hls segmenter wip

* log message

* close unused transcode sessions after 2 minutes

* use frame rate for 2s keyframes in hls segmenter

* add frame rate to media version

* fix segmenter framerate calculation

* automatically restart hls segmenter with next scheduled item

* cleanup

* update changelog

* decrease segmenter start delay

ErsatzTV.Core/Interfaces/FFmpeg/IFFmpegSegmenterService.cs

@@ -0,0 +1,14 @@
+using System.Diagnostics;
+using LanguageExt;
+
+namespace ErsatzTV.Core.Interfaces.FFmpeg
+{
+    public interface IFFmpegSegmenterService
+    {
+        bool ProcessExistsForChannel(string channelNumber);
+        bool TryAdd(string channelNumber, Process process);
+        void TouchChannel(string channelNumber);
+        void CleanUpSessions();
+        Unit KillAll();
+    }
+}

ErsatzTV.Core/Interfaces/Metadata/ILocalFileSystem.cs

@@ -15,5 +15,6 @@ namespace ErsatzTV.Core.Interfaces.Metadata
         IEnumerable<string> ListFiles(string folder);
         bool FileExists(string path);
         Task<Either<BaseError, Unit>> CopyFile(string source, string destination);
+        Unit EmptyFolder(string folder);
     }
 }