VBrick Systems Portal Server ETV v4.2.1 - Manual (Page 151)

Amino Set Top Box
ETV Portal Server Admin Guide 139
Table 18. Video Output with a Widescreen (16:9) TV:
TV Display Format Video Output
Widescreen TV 16:9 video plays normally and 4:3 video has black bars left and
right (pillar box). This relies on the TV responding to aspect ratio
switching signals on VBI line 23 (PAL only). On TVs that don't
respond to this signal, you must set the TV aspect ratio manually
to avoid a stretched or squashed picture.