If you’re a YouTube user on an iPhone, there’s a good chance that you’ve seen the Thumbnails option in the main YouTube screen. This is where you can choose to have your videos show as thumbnails or full-sized videos. To change this option on your iPhone, open the YouTube app and select “Settings.” In the “Thumbnails” section, change the “Thumbnail size” to something smaller than 100% of the screen. If you want your videos to always show as thumbnails, make sure to set this option to “Never.” Now that you’ve changed thumbnail size on your iPhone, it’s time to change thumbnail resolution. To do this, open the YouTube app and select “Settings.” In the “Thumbnails” section, change the “Thumbnail resolution” to something larger than 320x480. If you want your videos to always show as thumbnails, make sure to set this option to “Never.”
