Why can I render a 1440p video of Crysis 3 maxed out on YouTube and watch it flawlessly, when my graphics card could never handle such graphics?
Videos tagged with a "4K" icon on YouTube are produced and encoded at 4K/Ultra HD resolution [3]. However, not all playback devices can stream and play 4K content from YouTube at full resolution [3]. YouTube supports HLS ingest for premium content that requires high-quality and high-resolution video via HLS endpoint [1].
The reason you can watch 1440p videos on YouTube even though your graphics card couldn't handle the graphics is due to the increased definition it gives to the small images [1]. On cell screens, the icons become clearer, and on computer monitors it gives you a larger workspace [1]. Although 1440p can cause readability issues as the letters are well-defined but much smaller on the screen, it can be beneficial even on smaller screens [1]. 1440p is also commonly used over 1080p in high level gaming, where image quality is almost as important as frames per second [1]. An interlaced resolution is painted on the screen in alternating frames, with even number frames displaying only even numbered lines, and vice-versa [2]. By contrast, progressive resolutions constantly paint all lines, giving a much higher quality picture [2]. The number after the letter p in 1440p refers to how the resolution is drawn on the monitor, indicating if it’s progressive (1440p) or interlaced (1440i) [3].