What is VSYNC and how does it affect Video-SL?

What is V-Sync and why would you care?

To understand V-Sync you need to know a little about how monitors work. In general they have an image of what the screen should display and then draw this over and over. At any time the computer can change this image and so what we see on the screen changes.

This is normally fine but if the computer changes this image while the monitor is halfway through drawing to the screen then you can get images that looked like they have been torn.


V-Sync can solve this problem by making the computer wait until the monitor has finished drawing before changing the image. This also means that number of times that the image is changed (the frames per second) cannot be anything larger than the monitor refresh rate (normally between 60 and 90). Further, by limiting the number of times the image is changed there is less load on both the graphics card and CPU.

In Video-SL you can turn V-Sync on and off and you should be able to see a big difference in the frames per second reported.

Enabling V-Sync


To get rid of this tearing V-Sync must be enabled in 2 places. The first is within Video-SL; the Use V-Sync option is located in the Output tab on the Setup panel and is on by default.

The Use V-Sync Option is Located in the Output Tab

The Use V-Sync Option is Located in the Output Tab

The second is in the driver settings for your graphics card. This is always enabled in Mac OS X so the following only applies to Windows machines and has been broken into 3 sections based on the 3 most popular graphics card vendors: nVidia, ATI and Intel.

nVidia

To access the driver settings for you card you can follow the following process:

1. Right Click on the desktop and select 'Properties'
2. Select the tab called 'Settings' and click 'Advanced'
3. Select the tab that has the name of your graphics card and the nVidia logo
4. Select 'Performance & Quality Settings on the right
5. Find the 'global driver setting' called 'vertical synchronization'
6. Make sure that vertical synchronization is either 'On' or 'Application controlled'
7. Click 'Apply' and restart ScratchLIVE and Video-SL

ATI

To access the driver settings for you card you can follow the following process:

1. Right Click on the desktop and select 'Properties'
2. Select the tab called 'Settings' and click 'Advanced'
3. Select the tab called '3D'.
4. There are 2 options: Direct X and OpenGL. Select OpenGL
5. Look for the 'Wait for vertical sync' option and check that it is one of the following options: Default Off, Default On, or Always On. If it is then you have finished this process
6. If it is set to 'Always Off' click 'Custom' and set it to one of either 'Default Off' or 'Default On'
7. Click 'Apply' and restart ScratchLIVE and Video-SL

Intel

Unfortunately many Intel cards and their Windows drivers do not support v-sync and thus nothing can be done about the tearing issue. Those that do can have it set by turning off an option called 'Asynchronous Flip' which is not the same thing but should reduce tearing

1. Right Click on the desktop and select 'Properties'
2. Select the tab called 'Settings' and click 'Advanced'
3. Select the tab that has the name of your graphics card and the Intel logo
4. Click '3D Settings'
5. Change the 'Asynchronous Flip' option to Off
6. Click 'Apply' and restart ScratchLIVE and Video-SL

V-Sync Option May Cause Excessive CPU Usage on Some Windows Machines

There is a known issue with Windows machines and the Use V-Sync option in Serato Video which can cause excessive CPU consumption and a general feeling of sluggishness when playing videos. If you are experiencing this, you will need to disable V-Sync on your computer. Please read our article on V-Sync for an explanation on how to do this.