- The ideal image size for Twitter Cards is 800px by 418px, a 1.91:1 ratio. For App Cards, you can go with 800px by 800px for a 1:1 ratio.
- Videos can also be used in Twitter Cards. The recommended size for Website Card videos is 1200px by 1200px, or 1:1 aspect ratio. For App Card and Direct Message Card, the recommended size is 640px by 360px for a 16:9 ratio, or 360px by 360px for a 1:1 ratio.
- Twitter supports images that are JPEG or PNG format; no GIFs are allowed here.
- For best results, make sure your image is no larger than 3 MB.
- The approved file types are MP4 or MOV, ideally less than 30 MB in size, and no more than 1 GB when it comes to videos.
- Twitter advises a short video for these cards, so aim to keep it less than 15 seconds.
- For videos, place your logo in the upper left-hand corner.
- All Website Card videos are required to have closed captioning or text overlays.
source : https://www.adobe.com/express/discover/sizes/twitter