I was having issues with video playback of large (nearly 4k) videos. Part of the video was tearing, I knew the hardware was capable of playing the video ok, but in several applications the video would having tearing and playback performance wouldn't be very good.

After extensive trial and error, we determined the cause was the fact that we had switched off windows themes.

The machine in question was running Windows 7 Professional.

We tried this on a few other computers around and found the same thing. We had to switch themes back on to make the video play back reasonably. We were able to turn the themes service back on and off and each time consistently see the video play poorly with themes off and then dramatically improve when switched back on.

I (perhaps naively) assumed that the themes service was purely responsible for the visual styling of GUI elements. Clearly this isn't all the W7 themes service does.

I can not find via google or microsoft.com a complete description of what the themes services is responsible for.

Does anybody have - 1. Any idea why themes service being on would improve video playback ? 2. A complete description of what the themes service does ?

edit- in case it matters the video format was MP4 h.264, we tried both the build in Microsoft decoder, as well as LAV.

  • I've done a lot more googling and still can't find any explanation for this. It seems that disabling themes is often recommended as a system performance enhancer, it seems this is not always the case. – chip Aug 20 '14 at 23:11
  • This is only speculation: If the theme service is not running (this means using the classic theme and not the Aero theme), probably OpenGL and/or DirectX isn't used and hence not activated by your graphic card driver. So, no hardware acceleration, no smooth video playback. You don't include graphic card details, but checks the setting, if you can activate hardware acceleration by default. – mpy Aug 21 '14 at 17:08

Vsync is usually the reason for tearing.

Vsync in Windows Vista and later is handled by the desktop compositor and video applications. With classic theme, screen drawing reverts to GDI (think Windows XP but worse) where there is essentially no control over vsync. Nvidia driver will only force vsync in D3D or OGL applications.

The solution in this case is to enable vsync in your video application. If your current video application doesn't support vsync, get one that does. As far as I'm aware, that feature is for example supported in Media Player Classic Home Cinema.

You should also check if the video settings for refresh rate or frame rate are different when aero or classic are on.

  • Thanks ! I was able to test and confirm that vsync was the reason for the tearing. – chip Aug 24 '14 at 3:22

Disabling Themes services seem disabling Aero graphic engine alongside disabling Glass theming, with the system falling back to old style rendering - probably most of the code is from XP generation.

As you correctly recall, it is usually suggested as a way to recover resources, but my guess is that for high resolutions and modern graphic cards the old code is less efficient than new one (although the smaller footprint recovers some resources, which is good in some cases, but irrelevant in this case).

Probably there is not a real answer to this question, in the sense that different video cards and different drivers could work with different efficiency with the two graphic engines, so each case should be tested as unique: does the new Aero engine works better with that hardware, or should I fall back to old engine and free some resources as bonus?

As a role of thumb I can guess newer hardware will be fine tuned to work at best with Aero, to the point it can severely lag on the old engine, moreover average machine hardware in 2014 is far more powerful than in 2007 when Vista was published, so probably recovering resources turning off Aero is now no longer a good tradeoff and should not be longer recommended.

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