It will be helpful if you can answer carefully for beginners.

I use the WORDPRESS twentyseventeen theme, but the video quality of the top page is very poor.
I was able to set the video to the top page with the standard function, so I set it via youtube.
Appearance → Customization → Header media
>Or enter a YouTube URL.

If i play the video on youtube and increase the image quality from the settings, the video will be displayed neatly.
However, the quality of the video automatically played on the top page of wordpress is very bad.

Uploading on youtube is done with beautiful image quality.


How can I set the video on Wordpress to be displayed with good quality?