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/Encoder/EncoderAc3.cs

@@ -1,11 +1,7 @@
-using ErsatzTV.FFmpeg.Format;
-
-namespace ErsatzTV.FFmpeg.Encoder;
+namespace ErsatzTV.FFmpeg.Encoder;
 
 public class EncoderAc3 : EncoderBase
 {
-    public override FrameState NextState(FrameState currentState) => currentState with { AudioFormat = AudioFormat.Ac3 };
-
     public override string Name => "ac3";
 
     public override StreamKind Kind => StreamKind.Audio;