Video playback shows a vertical red/green line

Some users are facing a strange problem during video playback in Windows Media Player 12, a vertical red line is showing on the screen. VLC users are seeing probably a green line. Here is why.

It's an old issue, I've described in June 2011 for Windows 7 within this German blog post.

A vertical red line in Windows Media Player 12

A user has reported this behavior for Windows 7 in 2010 within Microsoft Answers-Forum as follows:

I have a red line running vertically down the middle of the screen when playing movies with media player on windows 7.

This happens with Windows media player and windows media player classic.  I can us vlc and I do not get the red vertical line running down the screen.  No matter what movie I play the line is there.  But it does not appear until I actually push play.  When I originally open the player I have a blank black screen.  But once I push play the movie starts and the red line is there.  Fast forward, rewind and pause, the line remains.  How do I solve this problem?

Well, the root cause and a solution was presented by Kristoffe Brodeur: It's the video demo mode in Catalyst video driver settings. Kristoffe wrote:

I have noticed that with Win7 after playing with the Catalyst settings in 'Avivio video ' you will see 'all settings ', then scroll all the way down and there will be a fieldset named 'video demo mode '.

1. If you have 'video demo mode ' settings 'enable demo mode ' check marked with split screen mode as an option, you will see a red line. To remove it, simply uncheck 'enable demo mode ', press 'apply ' and then close with 'ok '.
2. sometimes, you may see a green line, which is a driver for the video card, FFDSHOW or some other codec messed up, or the video card could be damaged, not pushed in all of the way in a pci, agp, or pci-e slot.

A plain but old working solution. I thought, the case would have been solved – but recently I was alerted from MS Answers about new posts. Obviously new ADM Radeon settings are enabling demo mode again. Here is a user post from 2015:

I went into my AMD Radeon Settings app and selected the tab "Video". Up in the top, right, corner, sure enough, there is a setting for demo. Mine was set to "Demo On". When I changed it to "Demo OFF", the red line disappeared. I just upgraded my AMD drivers to this latest version and then noticed the problem. Apparently, the "Demo" was on by default because I never changed any settings. Thanks you for the tip. Fixed my problem.

Another user suppose the mode has been set during driver update.

Yep – solved my problem by going into Radeon settings and turning off demo mode. Must have been turned on with the last driver updates.

Also in April and July 2016 some users are reporting this issue for Catalyst or Radeon Settings. One user delivers a hint, why some users are facing this issue.

I had absolutely the same problem here and managed to find a solution for it. The option 'Tearing Test' was enabled for me. It seems like I pressed Ctrl+T combination and turned it on (wanted to create a new tab in a browser). You can also try to use this combination or go to View -> Renderer Settings -> Tearing Test and disable it.

Maybe it's the Ctrl+T shortcut key combination that was accidentally used during operation, that enabled demo mode. Someone wrote: Right click on RADEON settings on your system stray and under VIDEO PROFILE choose default. That shall solve the issue.

VLC displays a green line

If users are seeing a green line during video playback in VLC player, there is also a settings solution, posted within the same MS Answers thread. Proceed the followings steps:

Tools menu –> Preferences –> Video –> Choose OpenGL under Output options –> Restart VLC.
Tools menu -> Preferences -> Video -> Uncheck "Accelerated Video Output (Overlay") -> Restart VLC.

That should solve the issue.