add watermark support to experimental transcoder logic (#654)

* wip

* fix songs again

* don't use lists of video and audio input files

* test concat command output

* move concat pipeline

* start to use ffmpeg state

* add ffmpeg state and audio state

* audio state is required

* attach input options directly to input files

* move filters to input files

* add watermark support

ErsatzTV.FFmpeg/Decoder/DecoderBase.cs

@@ -13,4 +13,9 @@ public abstract class DecoderBase : IDecoder
     public virtual FrameState NextState(FrameState currentState) =>
         currentState with { FrameDataLocation = OutputFrameDataLocation };
     public abstract string Name { get; }
+    public bool AppliesTo(AudioInputFile audioInputFile) => false;
+
+    public bool AppliesTo(VideoInputFile videoInputFile) => true;
+
+    public bool AppliesTo(ConcatInputFile concatInputFile) => false;
 }