(2019-12-13, 12:22)jfabernathy Wrote: In my case, I have many HDMI inputs into my AV Receiver and the RP4 is one of them along with a RP3B+. So the Overscan is off on the RP3/4s so they fill the screen.
There's a lot of misunderstandings about overscan and what it is.
Overscan (in this context) is purely a function of a display. It's a legacy feature that replicates the effect of 'overscanning' of a CRT display (i.e. an old tube display TV) where the horizontal and vertical scans made the electron beam(s) scan past the edges of the screen, cropping an amount of the picture left, right, top and bottom (effectively zooming the picture in slightly). Broadcast TV production could be quite ragged around the edges - so not showing the full width and height was also not a bad thing for viewers.
Modern flat screen LCDs, Plasmas and OLEDs often default to simulating this overscan - so a 1920x1080 source displayed on a 1920x1080 or 3840x2160 screen will often not show the full 1920x1080 image and will instead crop it and scale it - though you can often disable this on most TVs (though on some, only on native resolution sources), though finding the right menu and option description (Just scan, full pixel etc. can be tricky). On some displays these settings are source specific - so can be different for each HDMI port, internal tuner etc. On some displays this cannot be disabled - early plasmas with 1024x720 non-square pixel panels spring to mind...
Broadcasters currently work to a 5% graphics safe standard in the UK (assuming that only the 1728 x 972 centre portion will be displayed) these days. TV producers ensure their shows are produced with overscan in mind - and displaying them on overscanned displays is expected (nothing important should be outside of this safe area - though action safe is a little bit bigger)
So - displays exist with overscan.
The Raspberry Pi, at an OS level, includes overscan compensation. This is there to counteract the overscan of a display, and thus shrinks and scales down the Pi's video output and surrounds it with black bars, so displays with overscan will show the full Pi desktop (or other video output) without losing content that would otherwise be cropped in overscan (the black bars are cropped).
The Pi config.txt file has :
disable_overscan and overscan_left/right/top/bottom and overscan_scale settings to handle the configuration of overscan compensation.
Kodi, at an application level, also includes overscan compensation with the display calibration functionality which allows you to scale playback and GUI display within Kodi.
So - if you don't see black bars around your image that fills your screen, you can't assume all is well, as you could be seeing the result of Kodi or the Pi OS compensating for your TV overscan, with your TV still overscanning.
