Hardware.
Fullscreen may be doubling, even tripling the memory usage.
I did messure performance and memory usage in particular, here are the results (using NWjs):
Using WebM VP8:
Windowed Mode = ~120.000K
Fullscreen Mode = ~134.000K
Using WebM VP9:
Windowed Mode = CRASHED! (It used more and more memory until it reached it's limit.)
Fullscreen Mode = ~455.000K
How to reproduce the crash:
1. Open example project
2. Set to letterbox scaling
3. Run the project
4. Maximize the window (my native screen resolution is 1920x1080)
5. Notice that the memory usage is steadily increasing (task manager is running on my second screen)
6. Crash when reaching limit