Roku Developer Program

[groman00]

In the docs I see recommended Action Safe Zones for HD and SD. Does anyone know the safe zone for FHD?

From the docs:
Keep important visual elements within the Action Safe Zone, content outside the Action Safe Zone risks being cut off by the edge of the screen.
- The HD Action safe zone is 1150X646, offset from the upper left corner (0,0) by 64,35.
- The SD Action safe zone is 648X432, offset from the upper left corner (0,0) by 36,24.

[Komag]

Those are just rules-of-thumb. So you can do the simple math and extrapolate the 720p pixels up to 1080p

[EnTerr]

See here about recommended amounts
https://en.wikipedia.org/wiki/Overscan#Overscan_amounts

Roku does nothing about the overscan, it has a GIGO approach - but in most cases you don't have to do anything anyway because any decent TV or movie content has taken these into account. The only concern would be things like amateur video, subtitles or own UI