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/library.ts

@@ -462,6 +462,21 @@ export function clipVideoPath(owner: string, id: string) {
   return join(clipDir(owner, id), 'video.mp4')
 }
 
+export function clipLastFramePath(owner: string, id: string) {
+  return join(clipDir(owner, id), 'last-frame.png')
+}
+
+export function extendTempDir(owner: string, jobId: string) {
+  const dir = join(ownerRoot(owner), 'tmp', 'extend', jobId)
+  mkdirSync(dir, { recursive: true })
+  return dir
+}
+
+export function removeExtendTemp(dir?: string) {
+  if (!dir) return
+  rmSync(dir, { recursive: true, force: true })
+}
+
 export function clipThumbPath(owner: string, id: string) {
   const dir = clipDir(owner, id)
   for (const name of ['thumb.jpg', 'thumb.png', 'thumb']) {