Not adding subtitles into video

(async () => {
await ffmpeg.load();
ffmpeg.FS('writeFile', 'videoplayback.mp4', await fetchFile('./videoplayback.mp4'));
ffmpeg.FS('writeFile', 'subs.ass', await fetchFile('./subs.ass'));
await ffmpeg.run('-y','-i', 'videoplayback.mp4', '-vf', "subtitles=subs.ass", "-c:a", "copy", "out_bwf.mp4");
await fs.promises.writeFile('out_bwf.mp4', ffmpeg.FS('readFile', 'out_bwf.mp4'));
process.exit(0);
})();