Facebook has announced in their blog that the social network starting from August 19th – mobile News Feed ads will be compressed in order to “match the look and feel of the new Facebook design introduced earlier this year”.
Updates for mobile News Feed:
Fewer lines of primary text will show on mobile News Feed. Now only 3 lines of primary text will show on Facebook mobile News Feed, after which people will be prompted to click to view additional text.
Maximum media height for photos and videos will reduce to 4:5 on mobile News Feed. The tallest supported aspect ratio for images without links and for videos is now vertical (4:5). Media taller than 4:5 will be masked on Facebook mobile News Feed.
Facebook also says in its blog “The changes to text, photos and videos are designed to simplify our formats and improve the consistency of our mobile experience. This will help drive increased ad effectiveness and make it easier to use the same assets on Facebook News Feed and Instagram feed.”