This looks somehow like my app ClipMemo. The difference is that my app require you to create cards (called Memo in the app) by yourself. You select the start & end timestamp and you can review, repeat the clip. Besides YouTube it supports local video or other platform like Bilibili, China's counterpart of YouTube.

I'm not sure wheather my idea works or your work does. I'm also curious about which workaround solve this problem better. You can find ClipMemo on App Store.