Same as widescreen. FMV cutscenes are pillarboxed. HUD is spanned by default; for a centred HUD do the following:
Make a new text file. Paste in the following code (copied from the forum topic):
$Scale Gauges: no
#Gauge Config
$Base: (6000, 1200)
$Min: (1280, 640)
$Gauges:
+Messages:
Origin: (0.34, 0.0)
Offset: (8, 5)
+Wingman Status:
Origin: (0.66, 0.0)
Offset: (-92, 144)
+Auto Speed:
Origin: (0.66, 1.0)
Offset: (-64, -96)
+Auto Target:
Origin: (0.66, 1.0)
Offset: (-64, -120)
+Countermeasures:
Origin: (0.66, 1.0)
Offset: (-144, -166)
+Talking Head:
Origin: (0.34, 0.0)
Offset: (5, 56)
+Directives:
Origin: (0.34, 0.5)
Offset: (5, -106)
+Weapons:
Origin: (0.66, 1.0)
Offset: (-144, -257)
+Squad Message:
Origin: (0.66, 0.0)
Offset: (-197, 5)
+Escort View:
Origin: (0.66, 0.5)
Offset: (-159, -54)
+Mission Time:
Origin: (0.66, 1.0)
Offset: (-55, -52)
+Target Monitor:
Origin: (0.34, 1.0)
Offset: (5, -178)
+Extra Target Data:
Origin: (0.34, 1.0)
Offset: (5, -216)
+Multiplayer Messages:
Origin: (0.34, 0.5)
Offset: (8, -144)
+Voice Status:
Origin: (0.34, 0.5)
Offset: (8, -129)
+Ping:
Origin: (0.66, 0.0)
Offset: (-128, 5)
+Kills:
Origin: (0.66, 1.0)
Offset: (-144, -144)
+Fixed Messages:
+ETS Retail:
Origin: (0.66, 1.0)
Offset: (-144, -120)
$End Gauges
#End
Change the $Base dimensions to your resolution.
Save the file as hud_gauges.tbl in data\tables in the FSOpen installation folder (make the tables folder if it does not exist).
All HUD elements will now be centred in-game.