Description
If you're running windows and you got the choice of using either an integrated gpu card or a high performance NVIDIA processor you could run into some troubles with some shaders.
So, if the output video is glitchy after running the shadertoy-render script just make sure your python interpreter is using the right hardware, such glitch could be the result of using the integrated gpu graphics card as default.
To solve it, just go to Control Panel, go to "Manage 3D settings", then "Global Settings" and then you can choose under "Preferred graphics processor" to have "High Performance NVIDIA processor" to be used with your python interpreter (or virtualenv one). After you do that, the rendering process will be much faster and the glitches will be gone.
It'd be a good thing if the script warned about the requirements not being met at the beginning before starting to bake the video. Or maybe just showing the GPU which will be used in the process, so the user is aware of that in this particular case.
Hope it helps.