Add default video length setting and inherit duration when extending.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/api/extend.post.ts

@@ -2,7 +2,7 @@ import { existsSync } from 'node:fs'
 import { addStudioJob, kickStudioQueue, listStudioJobs, videoJobsBusy } from '~/server/utils/studioQueue'
 import { persistLoraFields, parsePostedLoraStack, listStudioLoras } from '~/server/utils/loras'
 import { readLoraStack } from '~/utils/loras'
-import { parseExtendDuration } from '~/server/utils/extendChain'
+import { clipPartDuration, clampVideoDuration } from '~/utils/videoDuration'
 import { defaultVideoSteps, isLtxWorkflow, LTX_DISABLED_MESSAGE, ltxWorkflowEnabled, parseVideoWorkflow } from '~/utils/videoModels'
 import { composePromptParts } from '~/utils/promptParts'
 import { nextFamilyPartName } from '~/server/utils/library'
@@ -25,7 +25,13 @@ export default defineEventHandler(async (event) => {
 
   const destFolder = publicLibrary(event).folders.find(folder => folder.id === source.folderId)
   const folderLocked = Boolean(destFolder?.protected && !destFolder.unlocked)
-  const durationSeconds = parseExtendDuration(body?.duration)
+  const parent = source.parentClipId
+    ? (() => { try { return getClip(owner, source.parentClipId!) } catch { return null } })()
+    : null
+  const inherited = clipPartDuration(source, parent)
+  const durationSeconds = body?.duration == null
+    ? inherited
+    : clampVideoDuration(body.duration, inherited)
   const promptPre = body && Object.prototype.hasOwnProperty.call(body, 'promptPre')
     ? String(body.promptPre || '').trim()
     : String(source.promptPre || '').trim()