Changing the size of the video icons ?

Forgive me as i'm not clear on the terminology, but i'm trying to change the size of the icons in my app which select HLS / MP4 on Demand or the next menu level. Trying to do like a more movie poster style rectangle laid vertical instead of a square. If anyone can point me to the syntax and variables that i need to modify in order to accomplish this i would sincerely appreciate it.

Thanks in advance,

Claudio