https://www.youtube.com/watch?v=GmtRmeU3tuo#t=1800s 《=複制的代碼，加上 #t=？？？？S 表示從第？秒開始播放1800秒=30分鐘
<iframe width="1280" height="720" src="https://www.youtube.com/embed/GmtRmeU3tuo" ?start=1800 frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> 《=嵌入的代碼加上?start=1800