以隐私增强模式嵌入视频或播放列表时，“订阅频道”按钮指向“找不到404”。
<iframe width="560" height="315" src="https://www.youtube-nocookie.com/embed/_owzPzUKuls" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
应该将用户重定向到https://www.youtube.com/signin?context=popup&next=https%3A%2F%2Fwww.youtube.com%2Fpost_login，而不是https://www.youtube-nocookie.com/signin?context=popup&next=https%3A%2F%2Fwww.youtube-nocookie.com%2Fpost_login