add channel start time template data

CHANGELOG.md

@@ -21,6 +21,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - Add framerate template data
     - `RFrameRate` - the real content framerate (or channel normalized framerate) as reported by ffmpeg, e.g. `30000/1001`
     - `FrameRate` - the decimal representation of `RFrameRate`, e.g. `29.97002997`
+  - Add `Channel_StartTime` template data
+    - This indicates the time that the transcode session started for the current channel
 - Add remote stream metadata
   - Remote stream definitions (yaml files) can now contain `title`, `plot`, `year` and `content_rating` fields
   - Remote streams can now have thumbnails (same name as yaml file but with image extension)

ErsatzTV.Core/Metadata/ContextTemplateDataKey.cs

@@ -0,0 +1,6 @@
+namespace ErsatzTV.Core.Metadata;
+
+public static class ContextTemplateDataKey
+{
+    public static readonly string ChannelStartTime = "Channel_StartTime";
+}

ErsatzTV.Infrastructure/Streaming/Graphics/GraphicsElementLoader.cs

@@ -249,6 +249,7 @@ public partial class GraphicsElementLoader(
             [FFmpegProfileTemplateDataKey.ScaledResolution] = context.SquarePixelFrameSize,
             [FFmpegProfileTemplateDataKey.RFrameRate] = context.FrameRate.RFrameRate,
             [FFmpegProfileTemplateDataKey.FrameRate] = context.FrameRate.ParsedFrameRate,
+            [ContextTemplateDataKey.ChannelStartTime] = context.ChannelStartTime,
             [MediaItemTemplateDataKey.StreamSeek] = context.Seek,
             [MediaItemTemplateDataKey.Start] = context.ContentStartTime,
             [MediaItemTemplateDataKey.Stop] = context.ContentStartTime + context.Duration