New Member - Two frames/partial frames

[Stokerup]

Having an argument with my son and we can't see eye to eye so I suggested to him that I join this forum to ask the experts. I'm sure there will be plenty of other things I can learn here too.

Here is the conundrum. Is it possible for a laptop screen (or computer LCD monitor e.g. HP L1910) which has a different refresh rate to the frame rate of a video it is displaying, to show two frames at once or partially if you happen to pause at the right time? I think it is possible. I don't think it would happen often but it could happen. He disagrees and says it's impossible.

[RealNC]

Here is the conundrum. Is it possible for a laptop screen (or computer LCD monitor e.g. HP L1910) which has a different refresh rate to the frame rate of a video it is displaying, to show two frames at once or partially if you happen to pause at the right time? I think it is possible. I don't think it would happen often but it could happen. He disagrees and says it's impossible.

If you disable vsync, sure. And not only two frames. There can be multiple frames. On a 60Hz screen with a game running at 600FPS with vsync OFF for example, there's 10 frames at once on the screen. But it won't be visible when you pause, because there needs to be motion to be able to tell. Otherwise all frames are the same. During motion, tearing is the observable effect of multiple frames on the screen. In the 600FPS@60Hz example, there's gonna be 9 tear lines.

Another way to obeserve multiple frames without motion would be a strobe pattern, where each frame has different color. One frame is fullscreen white for example, the next fullscreen red, then blue, etc. With vsync off and 600FPS@60Hz you'd never see the whole screen having the same color, but there would be 10 colors at once, each separated by a horizontal line.

Edit:

I forgot to mention that because LCDs and OLEDs are sample-and-hold displays, there's always at least two frames visible at the same time, even when vsync is eanbled. When the display starts scanning out a new frame, the previous frame is still on the screen and being "drawn over" by the new frame from top to bottom.

[Dalek]

Yes, this is called frame pacing. If you have an odd refresh rate (like 360hz) that doesn't correctly divide to a video's frame rate, you will see multiple frames appear. This is fixed with VRR being used in a player or switching to a refresh rate that divides properly.

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