Humax F1-4000T - Manual (Page 23)

Set the video mode for the TV SCART output.
Set the audio mode which is output from the TV SCART and
RCA/Cinch Jack. (Stereo/Mono)
Select the aspect ratio of TV which is connected to
STB (4:3 or 16:9).
Select the format which the video is to be displayed on screen.
When your TV set is 4:3 and video source is 16:9,
STB will display in Letter-box or Centre mode as selected.
When your TV set is 16:9 and video source is 4:3,
STB will display in the Pillar-box or Full mode as selected.
A/V Output Setting
Video Output (CVBS/S-Video/RGB)
Audio Output
Screen Mode
Display Format
GB22