As an app dev, how can I use this info from the feed to create this layout if I don't know the height or ratio of each image?
It's not about maintaining the ratio, it's about know what the ratio is so it can be used for design.
If this is in the feed, I have know idea if it's a banner image or a square image.
<podcast:images srcset="
400w /><podcast:images srcset="
400w />
