Write ffmpeg poster frames as a single image on Alpine.

FFmpeg 8 refuses a plain thumb.jpg output unless -update 1 is set.

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

server/utils/library.ts

@@ -415,7 +415,7 @@ export function clipThumbPath(owner: string, id: string) {
 
 function extractVideoThumb(videoPath: string, destPath: string) {
   return new Promise<boolean>((resolve) => {
-    const proc = spawn('ffmpeg', ['-y', '-ss', '0.2', '-i', videoPath, '-frames:v', '1', '-q:v', '4', destPath], { stdio: 'ignore' })
+    const proc = spawn('ffmpeg', ['-y', '-ss', '0.2', '-i', videoPath, '-frames:v', '1', '-update', '1', '-q:v', '4', destPath], { stdio: 'ignore' })
     const timer = setTimeout(() => {
       try { proc.kill('SIGKILL') } catch { /* ignore */ }
       resolve(false)