Screen Aspect

WD External Drives My Passport Wireless
4

The WD My Cloud App on iDevices does not use the full-screen video API when an HDMI adapter is in use.   It only does “Screen Mirroring.”   And since the output is only 1600x900 (IIRC) you’ll see a smaller picture.  

No way around it other than to use a different app that properly implements full-screen-video mode.

http://community.wd.com/t5/WD-My-Cloud-Mobile-Apps/iOS-HDMI-Out-and-WD-My-Cloud-App/m-p/791645/highlight/true#M4789