Green Line (chroma key?) on Video

[kinninigan]

I'm getting a partial green horizontal line in the upper left of videos, in both windowed and fullscreen modes, always persistent, no flickering. Looks like a green screen - looks like same color to me - chroma key bleed-through to me. More of a visual nag than a performance issue. I've gone through the video outputs, and this occurs in all modes that will render.

Again, it's at the upper left, top edge and progresses horizontally from 0,0 for about a tenth of the screen In fullscreen, and only hugs the top of the actual video in windowed mode.

You can view and Imgur gallery here: https://imgur.com/a/ucHvrrS
[edit]: Imgur's pop-up box kind of masks the problem. better views:
https://i.imgur.com/f7B78rH.jpg
https://i.imgur.com/W9dPsBX.jpg

This is kind of an old PC, Dell Optiplex 960 DT with
VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E] - the max video card this mobo can handle - running recently updated Ubuntu 16.04.7 LTS. [edit}: Unity/XServer (x11)
The monitor is an LG 34" set at 2560x1080 (21:9) rez. This is a secondary monitor in a two monitor set-up. The green line, however, occurs in Smplayer on both monitors.

Any explanation and/or fix or workaround would be great.

Thanks!

[edit]:
SMPlayer © 2006-2020 Ricardo Villalba <rvm@users.sourceforge.net>

Version: 21.1.0 (revision 9475)
Using Qt 4.8.7 (compiled with Qt 4.8.7)
Using MPlayer SVN r37540

[rvm]

I've never seen that green line in any computer where I tested smplayer.
Do you still have the problem if you use mpv instead of mplayer?

[kinninigan]

Thanks for the response.

I've tried changing it to mpv, even opening smplayer via terminal as superuser - both sudo and gksu, and it keeps defaulting back to "other" [/usr/bin/mplayer].
Neither mpv or mplayer allows for permanent selection, so no dice.

Only thing I can guess is that this v. of Ubuntu, with Unity DE, only has minimal, generic AMD video card support. OR, I selected something wrong upon install [I don't remember].

It's not a big deal; I can just zoom one step & it's out of frame. The main thing is that I've found a far superior replacement for VLC, I've been using SMplayer about three months & really like that it has so far handled any file type thrown at it right out of the box with no extensive and/or painful monkeying under the hood.

[rvm]