Synchronised media with decorative video

Hello!

In cases where there is synchronised media but the video portion of the media simply supplements the audio - for example, ‘whiteboard animations’ on YouTube where they draw what the narrator is saying - would you consider this audio only content? Because then it fails A 1.2.1 for not having a transcript. But if it is considered synchronised media and it doesn’t need a media alternative then it is only AAA 1.2.8 for not having a transcript? Or have I misunderstood?

Thanks

Sarah