Whenever I switch between 144p to a higher resolution it's obvious I need to download more data to view the same youtube video. Suppose I have buffered the whole video in 144p and I switch it to 720p then it definitely won't play if I shut off my connection. However, if I buffer in 720p and then switch to 144p youtube again downloads the whole video in 144p cant it just convert it into 144p when it has more than enough data with the 720p. In short, is all the data of a 144p video also stored EXACTLY the same as in a 720p video? (I am aware there are software which allows you to convert resolutions but that's not my question)
The answer to your question is yes, but that does not mean you can switch between streams (from higher to lower) as you please. YouTube does not support fully the ABS - HLS which means that selecting different stream in resolution selector resets/discards all of the already downloaded/pre-buffered chunks of the video stream, so you are back to square one with downloading/buffering it all over again.