Clips Live Titles fail on imported video

I am trying to use Apple Clips to add live titles to an existing video (recorded from the Camera app a few days ago, and imported to Clips through the Camera roll selection). I can't use the Live Subtitles feature, it keeps saying that live titles can only be added to clips with recorded vocal soundtrack. I am wondering if it is possible in any way to add titles to this video, maybe I need to split the video and audio and re-import the audio as the "recorded vocal sound track". I am using iPhone 15 Pro under iOS 18.3.2, I'd appreciate any help