“hmd mirror 1920x1080” or similar don’t work with the Vive.
Anyone knows how to get the mirror window to fullscreen (no matter if black border left and right or not)?
For the Vive use the r.setres x command instead of hmd mirror x.
Thank you NobleSpoon. Second time you help me out 
I owe you two beer
Always happy to help, especially when beer is involved 
You can also use the built-in Display Mirror functionality in the Vive, and just hit the Maximize button
Any suggestions on how to get a full HD window without the black bars? This also means a wider FoV.
Also wondering the same thing.
It’s a pretty ****** solution but this is what I ended up doing… I changed the resolution some, put the window up on my vertical 1440p monitor and then used bandicam to record a region. It’s not the greatest resolution in the end but it’s the best I’ve been able to get so far:
r.setRes widthxheight makes the size of the preview window that size, but my resolution is still super low inside that window, very blury.
Any way how to change that?
I’m using the Vive and UE4 4.17