Make marker preview duration ceiling configurable

Replaces the hardcoded maxMarkerPreviewDuration = 20 constant in
pkg/scene/generate/marker_preview.go with a configurable setting on
ConfigGeneral, mirroring the PreviewSegments wiring pattern.

- Default 20 preserves existing behavior for all installs
- Positive N sets the ceiling in seconds
- 0 (or any value <= 0) disables the ceiling, honoring explicit
  endSeconds verbatim
- Adds logger.Warnf for non-positive intervals to aid diagnosis of
  imported or malformed marker data
- Incidentally prevents zero/negative-duration ffmpeg calls that
  were possible under the previous logic

Context: closed issue #6852 (template non-conformance), Discussion
#6851 (mobile-first direction).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

graphql/schema/types/config.graphql

@@ -101,6 +101,8 @@ input ConfigGeneralInput {
   previewSegments: Int
   "Preview segment duration, in seconds"
   previewSegmentDuration: Float
+  "Maximum duration (in seconds) for generated marker preview videos. 0 disables the ceiling."
+  maxMarkerPreviewDuration: Int
   "Duration of start of video to exclude when generating previews"
   previewExcludeStart: String
   "Duration of end of video to exclude when generating previews"
@@ -239,6 +241,8 @@ type ConfigGeneralResult {
   previewSegments: Int!
   "Preview segment duration, in seconds"
   previewSegmentDuration: Float!
+  "Maximum duration (in seconds) for generated marker preview videos. 0 disables the ceiling."
+  maxMarkerPreviewDuration: Int!
   "Duration of start of video to exclude when generating previews"
   previewExcludeStart: String!
   "Duration of end of video to exclude when generating previews"

internal/api/resolver_mutation_configure.go

@@ -289,6 +289,7 @@ func (r *mutationResolver) ConfigureGeneral(ctx context.Context, input ConfigGen
 	r.setConfigBool(config.PreviewAudio, input.PreviewAudio)
 	r.setConfigInt(config.PreviewSegments, input.PreviewSegments)
 	r.setConfigFloat(config.PreviewSegmentDuration, input.PreviewSegmentDuration)
+	r.setConfigInt(config.MaxMarkerPreviewDuration, input.MaxMarkerPreviewDuration)
 	r.setConfigString(config.PreviewExcludeStart, input.PreviewExcludeStart)
 	r.setConfigString(config.PreviewExcludeEnd, input.PreviewExcludeEnd)
 	if input.PreviewPreset != nil {

internal/manager/config/config.go

@@ -119,6 +119,9 @@ const (
 	PreviewExcludeEnd        = "preview_exclude_end"
 	previewExcludeEndDefault = "0"
 
+	MaxMarkerPreviewDuration        = "max_marker_preview_duration"
+	maxMarkerPreviewDurationDefault = 20
+
 	WriteImageThumbnails        = "write_image_thumbnails"
 	writeImageThumbnailsDefault = true
 
@@ -1079,6 +1082,13 @@ func (i *Config) GetTranscodeHardwareAcceleration() bool {
 	return i.getBool(TranscodeHardwareAcceleration)
 }
 
+// GetMaxMarkerPreviewDuration returns the ceiling in seconds applied to
+// generated marker preview videos when the marker has an explicit end time.
+// Any value <= 0 disables the ceiling, honoring the marker's end time verbatim.
+func (i *Config) GetMaxMarkerPreviewDuration() int {
+	return i.getInt(MaxMarkerPreviewDuration)
+}
+
 func (i *Config) GetMaxTranscodeSize() models.StreamingResolutionEnum {
 	ret := i.getString(MaxTranscodeSize)
 
@@ -1918,6 +1928,7 @@ func (i *Config) setDefaultValues() {
 	i.setDefault(PreviewExcludeStart, previewExcludeStartDefault)
 	i.setDefault(PreviewExcludeEnd, previewExcludeEndDefault)
 	i.setDefault(PreviewAudio, previewAudioDefault)
+	i.setDefault(MaxMarkerPreviewDuration, maxMarkerPreviewDurationDefault)
 	i.setDefault(SoundOnPreview, false)
 
 	i.setDefault(UseCustomSpriteInterval, UseCustomSpriteIntervalDefault)

internal/manager/task_generate_markers.go

@@ -117,7 +117,7 @@ func (t *GenerateMarkersTask) generateMarker(videoFile *models.VideoFile, scene
 	g := t.generator
 
 	if t.VideoPreview {
-		if err := g.MarkerPreviewVideo(context.TODO(), videoFile.Path, sceneHash, seconds, sceneMarker.EndSeconds, instance.Config.GetPreviewAudio()); err != nil {
+		if err := g.MarkerPreviewVideo(context.TODO(), videoFile.Path, sceneHash, seconds, sceneMarker.EndSeconds, instance.Config.GetPreviewAudio(), instance.Config.GetMaxMarkerPreviewDuration()); err != nil {
 			logger.Errorf("[generator] failed to generate marker video: %v", err)
 			logErrorOutput(err)
 		}

pkg/scene/generate/marker_preview.go

@@ -11,16 +11,20 @@ import (
 
 const (
 	markerPreviewWidth        = 640
-	maxMarkerPreviewDuration  = 20
 	markerPreviewAudioBitrate = "64k"
 
+	// Fallback duration for markers that lack a usable explicit end time
+	// (nil EndSeconds, or EndSeconds <= start). Not user-configurable;
+	// markers wanting a specific duration should set an end time.
+	markerPreviewDefaultDuration = 20
+
 	markerImageDuration = 5
 	markerWebpFPS       = 12
 
 	markerScreenshotQuality = 2
 )
 
-func (g Generator) MarkerPreviewVideo(ctx context.Context, input string, hash string, seconds float64, endSeconds *float64, includeAudio bool) error {
+func (g Generator) MarkerPreviewVideo(ctx context.Context, input string, hash string, seconds float64, endSeconds *float64, includeAudio bool, maxDuration int) error {
 	lockCtx := g.LockManager.ReadLock(ctx, input)
 	defer lockCtx.Cancel()
 
@@ -31,11 +35,21 @@ func (g Generator) MarkerPreviewVideo(ctx context.Context, input string, hash st
 		}
 	}
 
-	duration := float64(maxMarkerPreviewDuration)
+	duration := float64(markerPreviewDefaultDuration)
 
-	// don't allow preview to exceed max duration
-	if endSeconds != nil && *endSeconds-seconds < maxMarkerPreviewDuration {
-		duration = float64(*endSeconds) - seconds
+	// Honor the marker's explicit interval when present and positive, capped
+	// by the configured safety ceiling. maxDuration <= 0 disables the ceiling.
+	if endSeconds != nil {
+		interval := *endSeconds - seconds
+		if interval > 0 {
+			if maxDuration <= 0 || interval <= float64(maxDuration) {
+				duration = interval
+			} else {
+				duration = float64(maxDuration)
+			}
+		} else {
+			logger.Warnf("[generator] marker at %.2fs has non-positive interval (end=%.2f); falling back to %ds default", seconds, *endSeconds, markerPreviewDefaultDuration)
+		}
 	}
 
 	if err := g.generateFile(lockCtx, g.MarkerPaths, mp4Pattern, output, g.markerPreviewVideo(input, sceneMarkerOptions{

ui/v2.5/graphql/data/config.graphql

@@ -25,6 +25,7 @@ fragment ConfigGeneralData on ConfigGeneralResult {
   previewExcludeStart
   previewExcludeEnd
   previewPreset
+  maxMarkerPreviewDuration
   transcodeHardwareAcceleration
   maxTranscodeSize
   maxStreamingTranscodeSize

ui/v2.5/src/components/Settings/SettingsSystemPanel.tsx

@@ -425,6 +425,14 @@ export const SettingsConfigurationPanel: React.FC = () => {
             return <></>;
           }}
         />
+
+        <NumberSetting
+          id="max-marker-preview-duration"
+          headingID="config.general.max_marker_preview_duration_head"
+          subHeadingID="config.general.max_marker_preview_duration_desc"
+          value={general.maxMarkerPreviewDuration ?? 20}
+          onChange={(v) => saveGeneral({ maxMarkerPreviewDuration: v })}
+        />
       </SettingSection>
 
       <SettingSection headingID="config.general.sprite_generation_head">

ui/v2.5/src/locales/en-GB.json

@@ -418,6 +418,8 @@
       "include_audio_desc": "Includes audio stream when generating previews.",
       "include_audio_head": "Include audio",
       "logging": "Logging",
+      "max_marker_preview_duration_desc": "Ceiling (in seconds) applied to generated marker preview videos when the marker has an explicit end time. Protects against unexpectedly long previews from imports or data entry mistakes. Set to 0 to disable the ceiling and honor the marker's end time verbatim.",
+      "max_marker_preview_duration_head": "Max marker preview duration",
       "maximum_streaming_transcode_size_desc": "Maximum size for transcoded streams.",
       "maximum_streaming_transcode_size_head": "Maximum streaming transcode size",
       "maximum_transcode_size_desc": "Maximum size for generated transcodes.",