Add clip extension from the last frame with FFmpeg stitching.

Let a finished player continue into a new MiniMax segment, then losslessly concat the parts and discard the intermediate files so the library keeps one extended MP4.

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

server/utils/pending.ts

@@ -20,6 +20,8 @@ export interface PendingJob {
   startedAt: number
   imageName?: string
   imageSubfolder?: string
+  extendTmpDir?: string
+  extendPart1Path?: string
 }
 
 function pendingRoot() {
@@ -68,7 +70,24 @@ export async function completePendingIfReady(pending: PendingJob) {
   const history = await fetchHistory(pending.promptId)
   const video = extractVideo(history, pending.promptId)
   if (!video) return null
-  const buffer = await downloadComfyVideo(video)
+  let buffer = await downloadComfyVideo(video)
+  if (pending.extendPart1Path && pending.extendTmpDir) {
+    if (!existsSync(pending.extendPart1Path)) {
+      removeExtendTemp(pending.extendTmpDir)
+      throw createError({ statusCode: 500, statusMessage: 'Extension source clip was missing during stitch' })
+    }
+    try {
+      buffer = await stitchExtension({
+        part1Path: pending.extendPart1Path,
+        part2: buffer,
+        tmpDir: pending.extendTmpDir
+      })
+    } catch (error) {
+      removeExtendTemp(pending.extendTmpDir)
+      throw error
+    }
+    removeExtendTemp(pending.extendTmpDir)
+  }
   const clip = await saveClip({
     ownerKey: pending.ownerKey,
     folderId: pending.folderId,
@@ -90,7 +109,9 @@ export async function completePendingIfReady(pending: PendingJob) {
   return {
     type: 'complete' as const,
     status: 'complete' as const,
-    message: pending.folderLocked ? 'Saved to the locked folder. Unlock it to view.' : 'Video ready',
+    message: pending.folderLocked
+      ? 'Saved to the locked folder. Unlock it to view.'
+      : (pending.extendPart1Path ? 'Extended video ready' : 'Video ready'),
     progress: 100,
     jobId: pending.jobId,
     clipId: clip.id,