If you have set the “Resize PIEWindow to Output Resolution” setting to true in the Project Settings, as far as I can tell, the window does get resized as requested, ie:
[Image Removed]If I request a render at 540x960, the resulting PIE window is ~540x992, but the actual viewport area given to the game window is the expected 540x960. (see bottom corner of screenshot for the resolution denoted by the red rectangle)
[Image Removed]If I request a render at 1920x1080, I get similar results;
[Image Removed]
(This feature does not work with Movie Render _Graph_ configurations right now, but does work with the default Movie Render Queue).
If setting the outputput resolution to 540x960 and when Resize PIEWindow To Output Resolution is enabled does not result in a tall vertical PIE window, then there is some other code involved that is fighting MRQ and you will need to debug. You can start with UMoviePipelinePIEExecutor::Start to verify what sized window is being requested:
TSharedRef<SWindow> CustomWindow = SNew(SWindow)
.ClientSize(WindowSize)
.AutoCenter(EAutoCenter::PrimaryWorkArea)
.UseOSWindowBorder(true)
.FocusWhenFirstShown(true)
.ActivationPolicy(EWindowActivationPolicy::Never)
.HasCloseButton(true)
.SupportsMaximize(true)
.SupportsMinimize(true)
.SizingRule(ESizingRule::UserSized);
If that is showing the correct resolution but it’s resolution is being changed after it is loaded, then you will need to look into SWindow::Resize, or SWindow::ReshapeWindow to see if some other code is calling that after PIE starts and is resizing the window again.
You should also try setting your DPI scaling for your monitor in Windows to 100% to ensure the mismatch is not related to HDPI support.