Changing the size of an embedded video

Testing the best embed code for a video if I want to change the size.

Directly from You Tube:
<iframe width="560" height="315" src="https://www.youtube.com/embed/rzeW741NLPY" frameborder="0" allowfullscreen></iframe>

I have  changed code to make the video smaller. The aspect ratio has been changed. I now get black lines on the top and bottom of the video.
<iframe width="320" height="266" src="https://www.youtube.com/embed/rzeW741NLPY" frameborder="0" allowfullscreen></iframe>

<iframe width="320" height="180" src="https://www.youtube.com/embed/rzeW741NLPY" frameborder="0" allowfullscreen></iframe>

The embed code has been altered but the aspect ratio kept the same by using an aspect ratio calculator.

Thanks to Anushika for the video.
https://phsanushikap.blogspot.co.nz/2017/04/tagimoucia-video-video-is-made-in.html?showComment=1493178347953#c6484729830277199045