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/watch.ts

@@ -1,4 +1,4 @@
-import { NODE_LABELS, isEncodingNode } from '~/server/utils/workflow'
+import { existsSync } from 'node:fs'
 import type { Job } from '~/server/utils/jobs'
 
 function classifyError(message: string) {
@@ -42,6 +42,7 @@ export function watchComfyJob(job: Job): Promise<void> {
       job.error = classifyError(error)
       emitJob(job, { type: 'error', error: job.error, message: job.error })
       if (job.id) deletePendingJob(job.id)
+      removeExtendTemp(job.library?.extendTmpDir)
       resolve()
     }
 
@@ -54,9 +55,24 @@ export function watchComfyJob(job: Job): Promise<void> {
       cleanup()
       try {
         job.video = video
-        emitJob(job, { type: 'status', message: 'Saving to library...', progress: 98 })
+        const stitching = Boolean(job.library?.extendPart1Path && job.library.extendTmpDir)
+        emitJob(job, {
+          type: 'status',
+          message: stitching ? 'Extracting last frame & stitching extension...' : 'Saving to library...',
+          progress: stitching ? 97 : 98
+        })
         if (job.library) {
-          const buffer = await downloadComfyVideo(video)
+          let buffer = await downloadComfyVideo(video)
+          if (stitching) {
+            if (!existsSync(job.library.extendPart1Path!)) {
+              throw new Error('Extension source clip was missing during stitch')
+            }
+            buffer = await stitchExtension({
+              part1Path: job.library.extendPart1Path!,
+              part2: buffer,
+              tmpDir: job.library.extendTmpDir!
+            })
+          }
           const clip = await saveClip({
             ownerKey: job.library.ownerKey,
             folderId: job.library.folderId,
@@ -87,11 +103,15 @@ export function watchComfyJob(job: Job): Promise<void> {
             imageSubfolder: job.library.imageSubfolder,
             promptId: job.promptId
           })
+          removeExtendTemp(job.library.extendTmpDir)
+          job.library.extendTmpDir = undefined
         }
         job.status = 'complete'
         emitJob(job, {
           type: 'complete',
-          message: job.library?.folderLocked ? 'Saved to the locked folder. Unlock it to view.' : 'Video ready',
+          message: job.library?.folderLocked
+            ? 'Saved to the locked folder. Unlock it to view.'
+            : (job.library?.extendSourceClipId ? 'Extended video ready' : 'Video ready'),
           progress: 100,
           filename: job.library?.folderLocked ? undefined : video.filename,
           subfolder: job.library?.folderLocked ? undefined : video.subfolder,
@@ -102,6 +122,7 @@ export function watchComfyJob(job: Job): Promise<void> {
         })
         deletePendingJob(job.id)
       } catch (saveError) {
+        removeExtendTemp(job.library?.extendTmpDir)
         const message = saveError instanceof Error ? saveError.message : String(saveError)
         job.status = 'error'
         job.error = `Video generated but library save failed: ${message}`