Youtube video quality Youtube app allows switching between normal and high quality videos. Is this normal and high quality depended on screen dpi or are they some fixed quality videos independent of mobile and tablets and their resolution?

For eg: Is the high quality video in my HTC Desier with resolution 480 X 800 same as in 1080p phones like HTC One?
If the quality is set to Auto, the video quality is dependent on the internet speed (faster connectivity better resolution, slower connectivity lower resolution), screen resolution, quality of the original uploaded video.

You can choose in the settings a resolution of your liking (240p, 360p, etc).
However, be aware that only resolutions that your phone or tablet can handle will be shown. For example, you will not see 1080p or 1440p if your screen can handle only resolutions up to 720p,

Source: Change the quality of your video