fix scaling image subs with vaapi (#2526)

CHANGELOG.md

@@ -29,6 +29,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Fix intermittent watermark opacity
 - Improve reliability of live remote streams; they should transcode closer to realtime in most cases
 - Dramatically improve stream startup time
+- VAAPI: fix scaling image-based subtitles (e.g. dvdsub)
 
 ### Changed
 - Do not use graphics engine for single, permanent watermark

ErsatzTV.Application/Streaming/Queries/GetPlayoutItemProcessByChannelNumberHandler.cs

@@ -283,10 +283,10 @@ public class GetPlayoutItemProcessByChannelNumberHandler : FFmpegProcessHandler<
 
             bool isComplete = true;
 
-            // if we are working ahead, limit to 45s
+            // if we are working ahead, limit to 44s (multiple of segment size)
             if (!request.HlsRealtime)
             {
-                TimeSpan limit = TimeSpan.FromSeconds(45);
+                TimeSpan limit = TimeSpan.FromSeconds(44);
 
                 if (duration > limit)
                 {

ErsatzTV.FFmpeg/Filter/ScaleSubtitleImageFilter.cs

@@ -0,0 +1,14 @@
+namespace ErsatzTV.FFmpeg.Filter;
+
+public class ScaleSubtitleImageFilter(FrameSize scaledSize) : BaseFilter
+{
+    public override string Filter =>
+        $"scale={scaledSize.Width}:{scaledSize.Height}:force_original_aspect_ratio=decrease,pad=w={scaledSize.Width}:h={scaledSize.Height}:x=-1:y=-1:color=black@0";
+
+    public override FrameState NextState(FrameState currentState) => currentState with
+    {
+        ScaledSize = scaledSize,
+        PaddedSize = scaledSize,
+        FrameDataLocation = FrameDataLocation.Software
+    };
+}

ErsatzTV.FFmpeg/Pipeline/VaapiPipelineBuilder.cs

@@ -516,16 +516,16 @@ public class VaapiPipelineBuilder : SoftwarePipelineBuilder
                 }
                 else
                 {
-                    var subtitleHardwareUpload = new HardwareUploadVaapiFilter(false);
-                    subtitle.FilterSteps.Add(subtitleHardwareUpload);
-
                     // only scale if scaling or padding was used for main video stream
                     if (videoInputFile.FilterSteps.Any(s => s is ScaleFilter or ScaleVaapiFilter or PadFilter))
                     {
-                        var scaleFilter = new SubtitleScaleVaapiFilter(desiredState.PaddedSize);
+                        var scaleFilter = new ScaleSubtitleImageFilter(desiredState.PaddedSize);
                         subtitle.FilterSteps.Add(scaleFilter);
                     }
 
+                    var subtitleHardwareUpload = new HardwareUploadVaapiFilter(false);
+                    subtitle.FilterSteps.Add(subtitleHardwareUpload);
+
                     var subtitlesFilter = new OverlaySubtitleVaapiFilter();
                     subtitleOverlayFilterSteps.Add(subtitlesFilter);
                 }