If your lag is everywhere (on desktop and in games), and you're on a Windows client, please switch to DirectX rendering in your client settings.
If you're experiencing lag in specific applications or games, but not everywhere, this is almost always caused by the application running in Fullscreen mode. If your game can run in Borderless Window/Borderless Fullscreen Mode, please change the game to run that way in the game's video settings. If you cannot change the game to that mode, you should then turn VSync Off in that specific game. This issue stems from how Fullscreen games render.
If your lag is everywhere (including on the desktop, please read the next two sections). These are prioritized in order of easiest to fix to hardest. Try the first fix before going on to the more complicated fix for computers running an older Intel HD Graphics GPU.
DIFFERENT REFRESH RATES
If your client computer and host computer have different refresh rates, it will result in what looks like stuttering in the video. We're trying to fix this issue, but for now, use your advanced settings on the peer (client) computer and type server_refresh_rate=60. That will force the hosting computer to a 60 FPS refresh rate. If your host computer is stuttering due to running games at too high of quality settings, please lower the quality setting on the game. A host that struggles to keep up with the demands of a game will send low FPS with Parsec while we assume the computer can handle 60 FPS.
INTEL DRIVER ISSUES
Intel HD Graphics 4000 and older do not support OpenGL well. You should switch your renderer to DirectX on the client and reconnect. We believe using a DirectX renderer will eliminate this terrible lag on older Intel CPUs.