Not all videos have subtitles. I do initially run yt-dlp with the extract subtitles parameter, then I check whether those subtitles were downloaded, then if not, I run whisper.
Have you found Whisper to be better than Google's automated subtitles? Might integrate it into my backup scripts myself.
Much better, actually. Try the large-v3 model, it's great. I use it via whisper-ctranslate2 which is a faster implementation.